CANOLA PRODUCTION & MANAGEMENT
ISSUED: 9-92
REVISED:
1. Introduction
(Lloyd Murdock, Jim Herbek and Steven K. Riggins)
Canola-quality rapeseed is one of the
world's leading edible oil crops. Soybean oil (30%), palm oil (16.7%),
rapeseed oil (13.9%) and sunflower seed oil (13.8%) collectively account
for almost 75 percent of total world edible oil production. Leading producers
of rapeseed (all types) are China, European Community (EC), Canada and
India. World production of rapeseed has increased faster over the past
two decades than that of any other oilseed. Over the last 15 years, rapeseed
production has achieved an annual average growth rate of seven percent
while soybean output grew annually at only four percent.
World trade in rapeseed and its products,
oil and meal, has also achieved spectacular growth. Rapeseed exports are
now the second largest volume oilseed traded following soybeans.
Canola is a specific type of rapeseed
associated with high quality oil and meal. The name "canola" identifies
the seed as having 2 percent or less of erucic acid in the oil and less
than 30 micromoles per gram of glucosinolates in the oil-free meal. Rapeseed
not meeting these standards cannot be termed canola.
Canola oil is lower in saturated fats
(6%) than any other vegetable oil. Other edible oils and their saturated
fat contents are: Safflower -- 9 percent; Sunflower -- 11 percent; Corn
-- 13 percent; Olive -- 14 percent; Soybean -- 15 percent; Peanut -- 18
percent; Cottonseed -- 27 percent; Lard -- 41 percent; Palm -- 51 percent;
Butterfat -- 66 percent; and Coconut Oil -- 92 percent.
Canola seeds contain about 40 percent
oil by weight and the oil is used as a salad and cooking oil and in other
processed foods. The meal is about 37 percent protein after oil extraction
and is a high protein livestock and poultry feed.
Rapeseed is grown in the cooler areas
of the world's agricultural regions such as North America, Northern Europe,
China and India. The oil has been used for centuries in Europe and Asia
as both a cooking and lamp oil and later as a lubricant and fuel. But only
recently were canola cultivars developed that reduce erucic acid and glucosinolate
levels in the oil and meal, respectively. This development made rapeseed
safe for human and animal consumption. Canada was the leader in this effort.
Since that time, consumption of canola oil has increased at a rate greater
than that of any other edible oil. It is a major edible oil in China, India,
Japan, Canada and many European countries. Japan is the only country in
this group that is not a major canola producer.
In 1985, the U.S. Food and Drug Administration
(FDA) granted GRAS (Generally Recognized as Safe) status to canola oil.
Since that time, domestic consumption has steadily grown.
Yet, production in the United States
is currently only about 10 percent of domestic demand. The driving force
behind increased demand is the health-conscious consumer. Because the oil
contains less than half the saturated fat of any other vegetable oil, has
a favorable mix of mono- and polyunsaturated fats, and, like other vegetable
oils, contains no cholesterol, the food industry is realizing canola's
benefits. All major food processors in the United States are evaluating
or using canola oil in their line of cooking oils and in an increasing
number of processed foods.
Kentucky seems well positioned to take
advantage of this opportunity.
•The crop is well adapted to the climate.
Yields of 70 to 90 bushels per acre have been obtained in research trials.
Yields from production fields have ranged from 20 to 60 bushels per acre
with an average of 35 to 40 bushels per acre.
•Canola fits well into our cropping
systems because it can be double-cropped with soybeans.
•Production practices, equipment needs,
production costs and the growing season for canola are quite similar to
wheat.
•Canola offers a profitable opportunity
to diversify crops and break disease and pest cycles established by using
present crops.
•Government feed-grain and wheat program
provisions have been modified to allow more flexibility in planting decisions
by farmers. Some of these provisions, such as the ability to plant canola
and other non-program crops on program crop base acreages, allowance of
double-cropped soybeans after canola on 0-92 land, and a marketing loan
rate that is favorable relative to the target price for wheat, encourage
canola production.
The acreage harvested in the state was
estimated at 1,000, 8,000, 20,000, 7,000, and 9,000 in 1987, 1988, 1989,
1990 and 1991, respectively.
Management decisions will make or break
any adopted crop. Canola will not be a success in Kentucky without increased
knowledge of canola management and an improved marketing system.
2. Plant and Growth Characteristics
(Jim Herbek and Lloyd Murdock)
What is Canola?
Plant Classification
Canola, an oilseed crop, is a genetically
altered and improved version of rapeseed. Rapeseeds as a whole are cool-season
annuals of the Cruciferae (mustard) family belonging to the genus Brassica.
The mustard family consists of about 3,000 species of plants mainly found
in the Northern Hemisphere. The name "crucifer" originated from the four
petals of the flowers arranged diagonally opposite each other in the form
of a cross. The Brassica genus contains many species of domesticated
crops grown for their oil, seeds, food (roots, stems, leaves, buds and
flowers) or forage. Even within a single species, crops have been developed
for different purposes. Being a member of the Brassica genus, rapeseed/canola
is closely related to mustards and vegetable crops such as cabbage, turnip,
kale, collards, cauliflower and broccoli. The word "rape" in rapeseed actually
comes from the Latin word "rapum" which means turnip. Some related weed
species included in the Cruciferae family are wild mustard, stinkweed,
shepherd's purse and common peppergrass.
Canola-quality varieties are presently
developed from either of two species of oilseed rape: Brassica napus
(also called Argentine rape, summer rape, winter rape or Swede rape) and
Brassica
campestris (also called Polish rape, summer turnip rape and field mustard).
Traditionally, farmers have grown canola varieties from these two species.
However, Canadian plant breeders recently have managed to cross the mustard
plant (Brassica juncea) with canola to produce a canola-quality
Brassica
juncea that has some advantages over the traditional canola varieties.
Some of these varieties may be available in five to 10 years.
Canola varieties currently grown in
Kentucky were developed from the B. napus species which is more
suitable for winter rapeseed production in the United States. This species
has a higher yield potential, better quality and later maturity than B.
campestris. It is largely self-pollinating, relatively tall (50 to
55 inch height), slightly more uniform in flowering and more prone to shattering
when ripe. Seeds are generally larger and brown to brownish black when
mature. Buds are at a higher level than recently opened flowers and upper
leaves encircle only half of the stalk.
B. campestris fits into the
short summer growth periods in Canada. This species is lower yielding,
largely cross-pollinated, earlier maturing than B. napus (10 to
14 days), shorter (about 40 to 45 inch height), less even in maturity and
more resistant to shattering. Its seeds are slightly smaller and yellowish
brown to brown when mature. The buds are at a lower level than recently
opened flowers and the lower part of leaf blades grasp the stalk completely.
History of Rapeseed/Canola
History suggests that rapeseed has
been cultivated for several thousand years with its origins in Asia. Rapeseed
was one of the few oil sources that could be successfully grown in the
cooler (temperate) areas of the world's agricultural regions. Rapeseed
was grown in Europe as early as the 13th century. In later centuries, it
was used as both a cooking and lighting oil. Rapeseed had limited industrial
use until the development of steam power, when it was discovered that the
oil was an excellent lubricant for steam engines. It was in the 1940s that
Canadian rapeseed production increased in response to a demand for the
oil as a lubricant. However, in the 1950s demand dropped with a change
to diesel power and to expanded use of petroleum products.
Edible vegetable oils are made up of
components called fatty acids which determine the use of vegetable oils
for edible or industrial uses. Some of these fatty acids are considered
essential in human diets while others are not. Brassica (rapeseed)
oils characteristically have a large amount of a long-chain fatty acid
called erucic acid. Prior to the 1960s, the erucic acid content of rapeseed
oil was not of particular concern when evaluating the oil's use for edible
purposes. During the 1960s, however, a considerable body of research began
to indicate that there could be negative health effects, particularly heart
abnormalities, associated with the consumption of erucic acid in rapeseed
oil. Because of the high levels of erucic acid in oil from traditional
rapeseed varieties, the oil was not considered safe for human consumption.
Concern about erucic acid prompted Canadian plant breeders to look for
new genetic sources with low erucic acid levels. This resulted in the development
of new varieties in the late 1960s and early 1970s with a low erucic acid
content. This represented a major quality improvement in the oil and provided
the opportunity for rapeseed oil to be used in food products for human
consumption.
While rapeseed oil quality was being
improved, Canadian plant breeders were also working to improve the quality
of the protein meal co-product. While rapeseed meal was an excellent source
of protein with a favorable balance of amino acids, its use was limited
by its high glucosinolate content. Most plants of the mustard family contain
glucosinolates (sulfur compounds). These compounds are responsible for
the flavor, odor and taste of mustards, radishes, turnips and other cole
crops. Traditional rapeseed varieties contained high levels of glucosinolates
in the meal which caused palatability, nutritional (depressed growth, lower
feed efficiency) and thyroid problems when fed in sufficient quantities
to livestock. The effect is more prominent in non-ruminant (swine and poultry)
than in ruminant animals. Canadian plant breeders initiated a search for
genetic material low in glucosinolates which was then utilized to successfully
reduce the levels low enough in varieties by the mid-1970s for the meal
to be used for livestock feed.
In 1978, the rapeseed industry in Canada
adopted the name "canola" to identify these new rapeseed varieties which
are genetically low in both erucic acid and glucosinolates and to distinguish
them from ordinary rapeseed. The name "canola" is an international registered
trademark of the Canola Council of Canada.
Rapeseed is not a new crop to the United
States. During the first half of this century, rapeseed (commonly called
rape) was primarily grown as an annual forage for all types of livestock.
Since then very little rapeseed, except for some industrial rape, had been
grown. Prior to 1985, the Food and Drug Administration (FDA) had banned
the sale of rapeseed oil for human consumption in the United States, primarily
because it was considered unsafe. This ban was imposed in the 1940s to
reduce possibilities of contamination of edible oils with the more toxic
industrial rapeseed oils. However, in 1985, largely as a result of the
development of the canola-type edible oils, the FDA gave GRAS (Generally
Regarded as Safe) status to rapeseed oil low in erucic acid for use in
U.S. food products. This opened the door for the United States not only
as a major potential market for the edible oil, but also as a producer
of canola to meet the demands of the edible oil market.
Canola Qualities and Terminology
There is often confusion about canola
and the terminology used to describe it. The term "canola" refers to a
quality standard; not a biological classification. Canola describes those
varieties of rapeseed which produce both a superior quality edible oil
and a high value animal feed.
In order to be considered as canola
or as being of canola quality, the standard requirements are an oil which
contains less than two percent of the total fatty acids as erucic acid
and a meal which contains no more than 30 micromoles of glucosinolates
per gram of air dry, oil free meal. Rapeseed not meeting these standards
cannot be termed canola and is considered unsafe for human or animal consumption.
Canola varieties having both low erucic
acid (<<2%) and glucosinolates (<<30 micromoles per gram) are
also referred to as double-low or double-zero (00) rapeseed. Canola is
also sometimes referred to as LEAR (low erucic acid rapeseed) because of
its low erucic acid content.
Canola oil's superior properties are
found to be very desirable as a liquid salad and cooking oil. It has also
been found suitable for use in shortenings and shortening oils as well
as margarines and margarine oils. The food industry is utilizing the oil
in an increasing number of food products.
There are public concerns about the
effects of saturated fats on blood serum cholesterol level, heart disease
and human health. Substituting unsaturated fat for saturated fat or reducing
intake of saturated fat is believed to reduce cholesterol levels and health
risks. No vegetable oil, including canola, contains cholesterol. However,
vegetable oils do vary greatly in the percentage of saturated fats they
contain. Canola oil has a lower level of saturated fats (only 6%) than
any other edible vegetable oil and also has a high proportion of unsaturated
fat containing a favorable mix of both mono- and polyunsaturated fats.
Other Rapeseed
There is another edible rapeseed of
low erucic acid content that is not of canola quality because it has a
high glucosinolate content. These varieties are referred to as single-low
or single-zero (0) rapeseed. Because of its low erucic acid content, single-low
rapeseed can also be referred to as LEAR. Most European rape was single-low
rapeseed which still had relatively high levels of glucosinolates, however,
they are now moving to varieties of double-low (canola) quality.
Industrial rapeseed values a high erucic
acid content which is in contrast to edible rapeseed oil. This rapeseed
type is often referred to as HEAR (high erucic acid rapeseed). Traditional
rapeseed varieties contained 20 to 40 percent erucic acid in their oil.
Newer, improved varieties of HEAR now range from 40 to almost 60 percent
erucic acid content. A minimum acceptable erucic acid content of 40 percent
is required for industrial use. Industrial rapeseed is used as a lubricant;
an additive in the production of cosmetics and toiletries, lacquers, detergents,
pharmaceuticals, plastic formulations and nylon manufacture; and as a raw
material in the chemical industry.
Although industrial rapeseed may contain
any level of glucosinolates, the meal usually has a fairly high content
making it unsuitable for animal consumption. Breeding improvements have
led to lower glucosinolate levels, resulting in greater economic value
to the meal.
Table 2-A lists the oil and meal characteristics
of the various types of rapeseed which have been discussed.
Table 2-A. -- Oil and Meal Characteristics of Types of Rapeseed.
| Type |
Other names |
Oil
(% erucic acid) |
Glucosinolate content of
meal (micromoles/gram) |
| Canola or "00" |
double-low
LEAR |
less than 2 |
less than 30 |
| "0" |
single-low
LEAR |
less than 2 |
greater than 30 |
| Industrial |
HEAR |
greater than 40 |
usually >30 but
can be <<30 |
Plant Characteristics
Canola is an annual. It is grown as
a spring crop (spring-seeded) in Canada and the areas in the Northern United
States that suffer severe winters. In more southerly latitudes, such as
Kentucky, canola can be grown as a winter crop (fall-seeded). Winter canola
usually out yields spring canola. When plants emerge in the fall, the seedlings
and early growth resemble cabbage, turnip or mustard greens. Plants go
dormant during the winter and much of the leaf tissue freezes.
The plant bolts rapidly in the spring
sending up a single flowering stalk. Canola grows to a height of four to
five feet. The portion of the stalk containing the pods will eventually
be 10 to 15 inches long.
Canola flowers are bright yellow and
a field in full bloom is quite showy. The yellow flowers are characteristically
four-petaled in the form of a cross. The rapeseed plant produces more flowers
than it has capacity to set pods.
Following pollination, an elongated
pod is formed with two chambers separated by a membrane with a single row
of seeds within each chamber. The green (tan when mature) pods will be
about 1/2- to 3-inches long, 1/8-inch wide and contain 15 to 30 small,
round seeds depending on species, variety and environment. Seeds are mature
12 to 15 weeks after spring regrowth.
The seeds of the B. napus species
are brown to black when mature. There are about 115,000 seeds per pound.
Seeds are about 1/32- to 3/32-inch in diameter but seed size varies with
variety and environmental effects.
Standards for canola are a test weight
of 50 pounds per bushel and a moisture content of 10 percent. Upon extraction,
canola seed yields about 40 percent oil by weight (versus 20% for soybeans)
making it one of the most efficient oil producing crops available. After
extraction, the residual meal contains 36 to 38 percent protein.
Growth Stages of Winter Canola
A grower who has an understanding of
how a canola plant grows can make more effective management decisions.
The growth of a canola plant can be divided into some recognizable growth
stages. The length of each growth stage is influenced by temperature, moisture,
light, nutrition, variety and environment.
Pre-Emergence (Germination)
Seed has been planted but prior to
plant emergence. The seed absorbs water and the root emerges growing downward.
The stem (hypocotyl) begins growing, pushing two leaf-like cotyledons (seed
leaves) up through the soil.
Seedling
The plant has emerged four to 10 days
after seeding. The two leaf-like cotyledons at the top of the stem have
unfolded and expanded. The root continues development downward. The growing
point of canola is above the soil between the two cotyledons. The exposed
growing tip makes canola seedlings susceptible to any hazard which results
in destruction of the seedling below the cotyledons.
Rosette
Seedling develops its first true leaves
within a week after emergence. The plant grows rapidly forming a dense
canopy of leaves. It quickly establishes a rosette with older leaves at
the base increasing in size and smaller, younger leaves developing in the
center. Stem length remains essentially unchanged although its thickness
increases. The root system continues to develop with secondary roots growing
outward and downward from the tap root. A plant can have from two to eight
or more leaves developed prior to winter dormancy depending on planting
date and other management factors. A rosette in at least the six to eight
leaf stage (six to 10 inches in height) is preferred.
Winter Dormancy
Growth slows and plants become dormant
as temperature drops and daylength shortens in late fall and early winter.
Leaves discolor (often showing purple discoloration) and die off. Much
of the leaf tissue freezes during the winter. As long as the crown does
not die, the plants are alive.
Spring Regrowth
Growth resumes in late winter and early
spring as temperature increases. New leaves develop near the soil surface
from the plant crown.
Budding and Bolting
Daylength and temperature trigger floral
initiation. A cluster of flower buds becomes visible at the center of the
rosette and rises as the stem rapidly bolts or lengthens. Leaves attached
to the stem unfold as the stem lengthens. Secondary branches arise from
axils of upper leaves of the main stem and also develop flower buds. Bolting
usually lasts one to two weeks.
The main stem reaches 30 to 60 percent
of its maximum length just prior to flowering. Rapid development and growth
of a large leaf area strongly influence pod set and early seed growth on
the main stem and first few secondary branches. Leaves at the start of
flowering, especially the upper ones, are the major source of food for
growth of stems and buds and their removal results in a large seed yield
loss.
Flowering
Flowering begins with the opening of
the lowest bud(s) on the main stem. Flowering continues upward with three
to five or more flowers opening per day. Flowering at the base of the first
secondary branch usually begins two to three days after initial flowering
on the main stem. During flowering, the plant continues to grow and to
develop new buds. Full plant height is reached by peak flowering. Flowering
normally lasts about three weeks but varies depending on weather conditions.
Flowers remain receptive to pollen
for up to three days after opening. Fertilization occurs within 24 hours
of pollination. After pollination and fertilization, the flower petals
wilt and drop two to three days after the flower opened. A young pod becomes
visible in the center of the flower a day after petals drop. Seed pods
develop from the bottom of the flower cluster and proceed upward since
the first buds to open on main stems and branches are the lowest buds.
During flowering, pods, flowers, and buds occur simultaneously on plants
with pods on the lowest part of stems and branches; open flowers above
them; and above the flowers, buds which are yet to open. All of the buds
that will develop into open flowers on the main stem will likely be visible
in B. napus within three days after the start of flowering. By mid-flower,
lower pods have started to elongate. By the time flowering is complete,
lower pods have started to fill with the seed enlarging.
Canola plants initiate more buds than
they can develop into productive pods. The flowers open, but the young
pods fail to enlarge and elongate and eventually fall from the plant. This
abortion of pods is a natural occurrence. Studies have shown that only
40 to 55 percent of the flowers produced on a plant develop productive
pods which are retained until harvest. If unfavorable growing conditions
or damage at early flower cause abortion or loss of flowers or pods, the
plant can recover by the development of those buds which otherwise would
have been aborted.
By mid-flower when lower pods have
started elongating, the stem has become the major source of food for plant
growth with a reduced amount from the declining leaves and a small amount
from the developing pods. The earliest developed pods have a competitive
advantage over the latest formed ones for the food supply. Any stress resulting
in a decrease in food supply during pod development results in fewer flowers
and fewer pods retained to maturity. Pods will also be smaller with fewer
and lighter seeds, especially in later branches and tops of branches.
Ripening
The ripening stage begins with the
petal falling from the last formed flower on the main stem. Canola ripens
from the bottom of the main stem and branches and continues upward. Thus,
pods at the bottom may reach maturity while pods at the top of the plant
are still developing. At the beginning of this stage, flowering may still
be continuing on some of the later, secondary branches.
During seed development, seeds attain
full size quickly. At full size, the seed initially is somewhat translucent
(resembling a water-filled balloon). At this time, the seed's embryo begins
rapid development within the seedcoat, filling the space occupied by fluid.
This results in a firm, green seed and an increase in seed weight. About
35 to 45 days after a flower has opened, seed filling is complete.
Seed filling is followed by a maturing
or ripening stage characterized by plant color changes. By the time flowering
has finished, most leaves, pods and stems have turned yellow. Seeds, contained
in two rows in the pod divided by a membrane, complete filling (physiological
maturity) at about 40 percent moisture and then slowly change color from
green to brown to black. Seed moisture is rapidly lost at one to three
percent or more per day, depending on environmental conditions. At 40 to
60 days after first flower, the seeds in the lower pods have ripened and
fully changed color. When 30 to 40 percent of the seeds on a plant have
begun to show seed color change to brown or black, the average seed moisture
is 30 to 35 percent. When all the seeds in all pods have changed color,
the plant dies.
Environmental Effects on Growth
Moisture at Seeding
Moisture is one of the major factors
controlling germination. Canola seed requires a high percentage of its
weight in water before germination begins. The soil moisture levels required
for winter canola germination and emergence are higher than either wheat
or barley. A loose or dry seedbed often results in slow or uneven germination
and may inhibit germination altogether until a rain occurs. Soil moisture
must be conserved during seedbed preparation. A firm seedbed reduces the
loss of moisture at the surface. Coarse textured soils dry more rapidly
than finer texture soils.
Water Requirements for Plant Growth
Water, either too much or too little,
can limit yield potential. Canola plants require large amounts of water.
The crop uses an estimated 18 to 22 inches of water to produce good yields.
Water use varies from 0.1 inch per day at the rosette stage to a peak of
0.3 inch per day during flowering. Heat and wind increase water use.
Moisture stress during the early vegetative
stages reduces leaf expansion and root growth. Moisture stress during flowering
and ripening results in large yield decreases from wilted leaves and reduced
branching, pods per plant, pod length, seed size and seeds per pod. The
flowering period and maturity are also shortened, especially when combined
with high temperatures. Research has shown that the response to irrigation
is greatest if water was maintained during flowering and pod-filling.
Canola requires a good mix of water
and air in the soil and will not tolerate excessive amounts of moisture.
Poorly aerated soils restrict root growth and affect water and nutrient
uptake. Canola can tolerate only brief periods of flooding or ponding.
Temperature Effects
Overall Effects on Growth
Canola has a reasonably wide adaptability
to perform well in many areas under variable temperatures. Canola prefers
relatively cool temperatures up to flowering. The minimum temperature for
canola growth is 41oF. This temperature is accepted as the threshold
below which little significant plant growth occurs. Since canola is a relatively
cool season crop, its best growth occurs above 54oF and below
86oF. The optimum temperature for maximum growth and development
has been estimated at just over 68oF. Temperature effects vary
with stage of growth.
Germination, emergence and early leaf
development are influenced by soil temperatures. Soil temperatures above
50oF result in a higher germination percentage, quicker emergence
and rapid leaf development. Because canola in Kentucky is planted in early
fall, low soil temperatures should not be a problem for germination and
emergence. Heat injury to seedlings can occur if air temperatures approach
90oF with soil temperatures above 100oF. Although
heat injury is associated with drought injury, excessive heat injures plants
even if soil moisture is plentiful.
Winter rapeseed must have several weeks
of temperatures near freezing with a minimum of two to four leaves for
it to undergo vernalization or it will not enter the flowering and reproductive
stages. At flowering, warm temperatures are preferred with soil moisture
readily available. Cool but non-freezing temperatures just prior to or
at flowering slow the rate of plant development, delay flowering, slow
flower opening and reduce pollen shed. High temperatures at flowering hasten
the plant's development, reducing the time from flowering to maturity.
This can decrease pod and seed numbers resulting in lower yields.
When pods are formed, canola is more
tolerant than at flowering to high temperatures. During seed maturation,
temperatures should be warm but not exceed 90 to 95oF for any
length of time. A combination of heat and moisture stress at this time
reduces seed yield and also oil content. Seed oil content is highest when
seeds mature under lower temperatures (60oF).
Winter Survivability
Winter canola undergoes a gradual hardening
process after several days of cold, near freezing temperatures that prepares
the plant for winter dormancy and allows it to withstand freezing temperatures
without serious damage. It is generally agreed that winter canola needs
30 days of above ground growth before the first killing frost to generate
enough growth for winter hardiness. Plant growth of six to eight leaves,
eight
to 10 inches in height and a large tap root (1/2-inch diameter) will develop
adequate carbohydrate reserves in the root to help the plant survive. If
this establishment does not occur, there is a greater chance of winter
kill and loss of the crop. Once established, winter canola is fairly hardy.
Snow cover also provides protection and increases chances for winter survival
under very cold air temperatures.
Winter survival is severely limited
by late planting. In three years of planting date studies at the University
of Kentucky, mid-October plantings did not survive two out of the three
years; early October plantings did not survive one out of the three years;
early and mid-September plantings survived all three years although some
loss did occur during a year of very cold temperatures.
Although canola can withstand cold
air temperatures, it has been known to succumb in very cold winters with
little snow cover. The critical temperatures at which plant damage or kill
occurs is somewhat nebulous since other factors such as snow cover, amount
of cold hardening, plant developmental stage, soil moisture conditions
and other cultural practices influence the degree of susceptibility of
plants to temperature. It has been observed that winter canola can withstand
24oF air temperatures with no damage. Below this, leaf damage
can occur. In fact, much of the leaf tissue eventually freezes during the
winter. Despite the loss of leaf tissue, the plant is not killed if the
crown is healthy and alive. In late winter, if you see new leaves or the
crown has green tissue, the plant has survived. Usually plant loss will
not occur unless temperatures drop below 0oF. In fact, well
established plants survived temperatures of -10 to -15oF in
December of 1989 with only a 30 to 50 percent stand loss. Some literature
suggests that cold soil temperatures (-5oF or less) are more
critical to winter loss of canola.
Waterlogged soils seem more conducive
to winter loss. On these soils, heaving of smaller plants without an established
root system and subsequent exposure of crowns is more likely. It has also
been suggested that a combination of waterlogged soils and freezing temperatures
promotes the rupture of crowns resulting in stand loss. It has also been
noted that fungal or bacterial infections and infestation by fly maggots
can cause plant loss in association with freeze damaged or otherwise weakened
plants. This phenomenon is known as winter decline syndrome.
Spring Freezes
Freezing temperatures are likely in
Kentucky in late March and early April, a time when canola has bolted and
may have initiated flowering and pod development. These freezing temperatures
have the potential to cause injury. The temperature at which freezing injury
occurs varies with the plant's stage of growth, moisture content and the
length of time the temperature remains below freezing. The length of time
that freezing temperatures occur is important. A large drop in temperature
lasting only a short time may not damage canola, while a small drop of
a few degrees lasting for several hours may cause severe damage.
Canola is most susceptible to freezing
temperatures at flowering. Temperatures just slightly below freezing (31
to 32oF) can kill open flowers, whereas temperatures of 27oF
are needed to cause injury on developing pods or unopened flowers (buds).
Frost at flowering delays maturity but results in only minor reductions
in yield. This is because canola plants initiate more flowering buds than
they can develop into pods. Since only about 50 percent of the flowers
develop into mature pods, any damage or loss of early flowers or pods causes
the plant to recover by development of later flowering buds which would
otherwise have been aborted. Frost during flowering usually causes flower
abortion only on those flowers open at the time the frost occurred. Frost
after the flowering stage, which is unlikely in Kentucky, can result in
significant yield reductions.
Hail Damage
Research has shown that canola plants
have a remarkable ability to recover from hail damage at certain growth
stages. Plants recover remarkably well from damage occurring in early vegetative
growth stages. However, in Kentucky hail damage is more likely to occur
in the late vegetative and reproductive stages. Plants injured in the late
vegetative or early flowering stages can recover because of well-established
root systems and the ability to develop secondary flower clusters. When
buds and flowers are lost due to injury, the plant recovers rapidly by
the development of flowers which normally would have been aborted. Plants
can also develop flowering branches from growth buds lower down on the
plant and replace, somewhat, the lost buds, flowers and pods. Seed yield
depends on the percentage of leaves and branches lost as well as the progression
of flowering when the hail damage occurred. The greater the percentage
of branches lost, the greater the seed yield loss. Also the longer that
flowering has progressed before damage from hail, the greater the seed
yield loss. Maturity is also delayed.
If hail damage occurs during pod filling
or ripening, plant recovery is greatly reduced. Even if plants do rebranch
and flower at this stage, maturity is greatly delayed and redevelopment
will likely be hindered by environmental factors (heat, moisture stress).
Seed yield losses at the ripening stage depend directly on the loss of
branches, pods and seeds.
3. Cultural Practices
(Jim Herbek and Lloyd Murdock)
Field Selection
A medium textured, well-drained soil
is best for canola, although it will grow over a wide range of soil textures.
Since canola does not tolerate waterlogged conditions, it should not be
planted on fields prone to standing water, flooding or poor drainage. Heavy
clay and waterlogged soils also increase the risk of heaving if not planted
early for a well established root system. Soil compaction, soils that tend
to crust and a lack of surface soil moisture at planting time can also
affect canola establishment.
Select fields and rotation systems
that prevent a build up of pests (insects, diseases and weeds). Allow at
least four years between canola crops on the same field. This is particularly
important for fields that have been infected with sclerotinia white mold
or blackleg and also applies to any adjacent fields. Avoid fields infested
with garlic, wild mustard and hard-to-control weeds. Plan ahead so that
residual herbicides used on the previous crop do not carry-over in the
soil and adversely affect canola. Avoid planting within a mile of a field
of industrial rape to avoid contamination which may result in lower seed
quality and grade standards.
Variety Selection
Variety selection is important for
producing a canola crop that contains desirable performance traits and
also quality seed. Plant only those cultivars with canola-quality standards
(an oil with less than two percent erucic acid and a meal with less than
30 micromoles glucosinolates per gram). This is essential for canola to
be an economically competitive, marketable product. Because of the oil
and meal quality differences among the various types of rapeseed, it is
important to not plant varieties of unknown or unsubstantiated quality.
Other characteristics to choose in
a canola variety are: high yield potential, acceptable test weight (50
lbs/bu), winter hardiness and lodging resistance. Relatively early maturity
is also desirable if the canola is to be double-cropped with soybeans.
While disease resistance is a desirable trait, there is currently no varietal
resistance in canola to most diseases common in Kentucky. However, there
is moderate resistance to blackleg in some canola varieties and these should
be used in production areas where blackleg is a concern. As varietal development
continues, additional disease resistance should be forthcoming.
There are two types of canola available
for planting: spring and winter. Spring types are grown in areas where
winterkill is a problem for fall seedings. Winter types are fall-seeded
and require a specific amount of chilling temperature for vernalization
(flower induction). Winter canola fits best into Kentucky's cropping systems,
has a higher yield potential and has sufficient cold hardiness to survive
most winters.
Most varieties presently sold in Kentucky
were developed in Europe. Limited testing and experiences of farmers have
shown these varieties to be good and fairly well suited to our conditions.
Varietal development is proceeding at a rapid pace and new varieties should
have higher yield potential, earlier maturity and improved resistance to
shattering, disease, and lodging.
Canola can be hybridized and breeding
companies are currently developing hybrids. Some hybrids should be on the
market within the next three to five years and should give a 10 to 20 percent
yield advantage over current varieties.
The University of Kentucky began to
evaluate winter varieties of canola in 1987-88 at the Kentucky Agricultural
Experiment Stations at Lexington and at Princeton, Kentucky. Growers interested
in an annual performance report of these variety trials should contact
the University of Kentucky College of Agriculture or their local county
Extension office.
Seed Selection
Only certified seed should be used
since it assures you of true canola quality with no contamination from
mustards, high erucic acid rapeseeds and weed seeds. It has also been tested
for germination and purity to ensure seed quality. Because product quality
is critical for canola, producers must be sure of the genetic purity of
the seed. Proper seed conditioning and fungicide seed treatments are recommended
to avoid certain diseases. In Kentucky, all classes of certified seed must
be treated with an approved seed treatment fungicide to control blackleg
fungus.
Using bin-run (second generation) seed
is risky and does not assure purity, seed quality or that canola standards
are met and may result in loss of canola double-low quality. Also to avoid
cross-pollination between canola and other types of rapeseed, canola should
not be grown in close proximity of the other types.
Certified Seed Production
Certain field, rotation, and seed requirements
and standards apply to certified winter canola production. Growers interested
in producing certified winter canola should consult the latest "Kentucky
Seed Certification Standards" published annually by the Kentucky Seed Improvement
Association.
Tillage and Seedbed Preparation
Seedbed preparation is important. Conditions
that promote rapid germination and early, uniform stands and growth are
important for weed control, winter hardiness and yield. The seedbed should
be fairly level, well-packed and moist throughout its depth. The soil surface
should have a good granular structure. If the seedbed is too fine (overworked),
it can result in loss of surface soil moisture and promote crusting; if
too coarse, poor seed placement and moisture loss. Rollers or cultipackers
should be used with or after the last tillage operation to firm the soil
to allow proper seeding depth and to provide good seed-soil contact.
The no-till method of planting is a
means of eliminating tillage for seeding canola. By eliminating tillage,
no-till also allows earlier planting.
Planting Date
Canola should be planted in September
in Kentucky. Planting dates of September 1 through September 25 should
provide the best yields. Seeding too early or too late can increase the
likelihood of winterkill. A good rule of thumb is to plant canola approximately
four to five weeks before the normal planting date for winter wheat. Planting
too early can result in winter injury if bud formation and stem elongation
occur prior to winter dormancy. Late plantings (after October 1) reduce
yields, increase heaving (due to smaller root system) and reduce winter
survivability. Generally, canola needs 30 days (6-8 leaves) before the
first killing frost to generate enough growth for winter hardiness. Based
on 1989 results, planting date studies showed a 1.7 percent yield loss
per day when planting after September 20 but before October 1. Planting
after October 1 resulted in a 2.1 percent per day yield loss. Ideal planting
dates for optimum yields vary from region to region as plantings move North
(slightly earlier) or South (slightly later).
Planting date also effects maturity,
canopy cover and weed control. An October planting results in reduced fall
foliage production (canopy cover) which can allow weed growth and can delay
the harvest date.
Planting Methods
The most common planting methods are
broadcast and drilled. The broadcast method can save time and reduce machinery
requirements but stand reliability is sometimes reduced using this method.
It is very dependent on good surface soil moisture at seeding or rainfall
immediately following seeding. The major disadvantages of broadcast seeding
are shallow placement of seed, uneven planting depth, poor seed distribution
and a greater dependency on moisture. Care must be taken to assure good
seed distribution and soil coverage. Working the seed into soil after broadcasting
is a critical step. A roller or cultipacker is the most common method and
gives good seed-to-soil contact and also retains moisture. This also prevents
a deep seed placement problem as other implements can place the seed too
deep.
Drilling is the most reliable and preferred
method. However, proper drill calibration and settings are required with
this method to do a good job of seeding. Advantages of drilling include
better seed placement, better seed-to-soil contact and uniformity of stand.
Depth placement is important since moisture is usually critical at this
time of year and deep seed placement results in failure. Cultipacking is
recommended prior to drilling to firm the seedbed and help control the
seeding depth.
Grain drills, particularly late model
drills, can effectively plant canola through the main seedbox. However,
some grain drills may not close down enough for the small seeding rates
needed and may require special drive attachments or small seed attachments.
Calibration is needed with any seeding method but is particularly essential
if using a drill.
Although more difficult, the no-till
method of seeding can be used with canola. Use of a suitable no-till drill,
proper calibration and no-till planting experience are needed to ensure
good stand establishment. Depending on the seed drill capabilities, excessive
crop residue on the soil surface can cause uneven seed placement. However,
no-till drills that can deliver precise seed depth placement can make no-till
planting successful. If the field is heavily infested with weeds or grasses,
a contact herbicide at planting would be important for no-till planting.
Producers in Kentucky have no-tilled canola into previous crop residue
with good to excellent results.
Seeding Depth
Since canola seeds are very small,
careful placement is required at a relatively shallow depth. The ideal
seeding depth is 1/2-inch in a firm seedbed. The range can be from 1/4-
to 1-inch. It is important to plant into moisture within this range, unless
rain is imminent. Deeper depths delay emergence, reduce seedling vigor,
and delay fall growth and development. It is difficult for canola to force
its way through thick soil cover or crusts. At shallower depths the seedbed
may dry too fast for uniform germination.
Seeding Rates
Canola is a very flexible plant that
can adapt to a wide range of populations due to its ability to branch.
Research studies have shown similar yields for seeding rates ranging from
four to 10 pounds per acre if an adequate plant stand has been obtained.
A harvest population of six to 10 plants per square foot is considered
adequate for top yields. Significant yield differences are not usually
found unless populations at harvest are under three to four plants per
square foot or higher than 15 plants per square foot.
Carefully evaluate before destroying
a crop that has a spring stand of only one to two plants per square foot
since canola can compensate for wider spacing between plants by promoting
branching. In a stand density study conducted at the University of Kentucky,
even at one to two plants per square foot, yields were 60 to 70 percent
of the optimum yield which occurred at six to eight plants per square foot.
These plants compensated by producing more basal branches although they
were not as productive as the earlier, main stem branch. Even though plant
stands of one to two plants per square foot have given relatively good
yields, it is still recommended that seeding rates be utilized to achieve
at least five to seven plants per square foot.
Low seeding rates often produce thin
stands and result in more weed problems because they cannot effectively
form a complete canopy. Although thicker stands can promote earlier and
more uniform maturity and thinner stalks which are easier to harvest, populations
above 15 plants per square foot do not increase yield, may cause lodging
and also increase chances of disease. Higher seeding rates may be used
if planting is delayed or when seed placement is affected by surface residue.
The average seed size of canola (Brassica
Napus) is about 115,000 seeds per pound (with a range of 80,000 to
150,000 seeds per pound). With average seed size, a five to six pound per
acre seeding rate would plant about 13 to 15 seeds per square foot. The
percent emergence varies with soil and moisture conditions and seeding
methods. Check the seed tag for seed size (seed count per pound) to determine
the appropriate seeding rate. The recommended seeding rates are: 4 1/2
to 6 pounds per acre for drilling and 6 1/2 to 8 pounds per acre for broadcast
seeding. The higher seeding rate for broadcast seeding is due to expected
lower emergence.
Row Spacing
Studies have shown row widths between
seven inches and 14 inches to have little impact on yield. Row spacings
below seven inches might result in small yield increases under certain
conditions. Likewise, row spacing above 10 inches could result in small
reductions in yield. The narrower row spacings of six to eight inches provide
quicker row closure and reduce weed competition. The six- to 10-inch row
spacing provided by most commercial grain drills is acceptable for winter
canola production.
Fertilization
Soil Testing
A soil test is the most accurate method
of determining the soils nutrient status. Reliable recommendations for
phosphorus, potassium and lime can be made from a soil test.
Nitrogen
Canola responds to a fairly high level
of nitrogen. The present recommendation is 120 pounds of nitrogen per acre.
With good stands, lower rates may reduce yields. Higher rates may occasionally
result in a higher yield, but it also increases chances of lodging and
disease susceptibility. Most or all of the nitrogen should be applied at
green up in the spring (March). If possible, it should be applied before
budding and stem elongation to prevent damage to the main stem from ground
spreading equipment. Ground equipment should never be used when the soil
is frozen. Kentucky research shows no benefit for fall application of nitrogen.
In many cases, additions of nitrogen in the fall (even in small amounts,
20-30 lb/ac.) increased fall growth and contributed to winter kill. In
some years, the winter loss, due to fall nitrogen, has been significant.
Large amounts of nitrogen carried over from the preceding crop can also
produce the same results. If fall nitrogen is needed for some reason, no
more than 30 pounds nitrogen per acre should be added.
A nitrogen deficiency results in stunted
growth with a pale green color, early flowering and early maturity. The
application of liquid nitrogen could result in scorched leaves, depending
on weather and method of application.
Phosphorus and Potassium
Both of these nutrients should be applied
in the fall according to soil tests. Recommendations in the following table
are based on crop requirements and Kentucky soil characteristics. The recommendations
may change as information is gained from research with this crop.
Tentative results indicate that canola
is very sensitive to phosphorus and recommendations should be liberal for
this nutrient. The crop appears to be less sensitive to potassium and the
recommendations can be conservative.
Table 3-A. -- Phosphorus and Potash Recommendations.
Pounds per acre to apply
| Soil test level |
P2O5 |
K2O |
| High (above 60P, 300K) |
0 |
0 |
| Medium (30-60P, 200-300K) |
0-85 |
0-40 |
| Low (below 30P, 200K) |
85-120 |
40-80 |
Sulfur
Canola is sensitive to sulfur deficiency. However, research has not
shown a need for sulfur application to this crop or any other sulfur-sensitive
crop in Kentucky. If a deficiency is identified, it can be corrected with
a sulfur application of 15 to 20 pounds per acre.
Lime
For best performance of the canola
and succeeding crops in the rotation and for efficient use of herbicides
and fertilizers, the pH should be maintained between 6.0 and 7.0.
Fertilizer-Seed Contact
Because canola is sensitive to direct
seed contact with fertilizers, nitrogen and potassium should not total
more than 10 pounds per acre, if placed with the seed.
Crop Rotation
It is important that canola be in a
rotation with other crops. The ideal rotation is to plant canola or other
rapeseed or Brassica crops (cabbage, broccoli, etc.) only once every
five years to reduce potential pest problems. This rotation helps to minimize
the buildup of difficult to control weeds, insects and diseases that continuous
planting of canola may perpetuate.
Plan ahead in your rotation systems
so that herbicide residues from a preceding corn or soybean crop do not
limit your options for planting canola. Canola is sensitive to some herbicides,
particularly broadleaf herbicides, depending on the rate used and other
factors involved (weather, tillage, etc.). Herbicide residues from Scepter,
Canopy, Classic, Pursuit and Atrazine (particularly high rates) can damage
canola so caution is advised for planting canola following crops in which
these herbicides have been used.
Volunteer canola can be a problem in
succeeding crops. However, it can be easily controlled through use of a
rotation and use of herbicides in the succeeding crop that are labeled
for mustards.
Cropping systems in Kentucky that best
lend themselves to canola are set-a-side, fallow and early planted, medium
maturity corn.
Conservation Aspects
Ground cover by the canola plant is
excellent. If the crop is planted in mid-September, there will be virtually
a 100 percent ground cover prior to winter. This cover, along with an excellent
root system, protects the soil from erosion as well as or better than a
small grain cover crop.
The residue produced from canola is
about the same as that produced with small grain, although the seed yields
will be about two-thirds to three-fourths that of wheat. The residue appears
to decompose more quickly than small grain residue.
Double-Cropping
Being a winter crop, canola gives Kentucky
farmers an alternative to small grains and offers the same double-cropping
potential with soybeans. Harvest maturity for wheat and canola are very
similar with canola being as much as three days earlier in some seasons.
With the tremendous genetic variability available in canola germplasm,
earlier maturing varieties may be available in the future which should
result in a yield advantage for double-cropped soybeans. Research studies
at the University of Kentucky compared soybeans double-cropped after canola
and wheat on the same planting date. Two-year results have shown a two
to seven bushels per acre yield advantage for soybeans double-cropped after
canola as compared to soybeans double-cropped after wheat. No definite
conclusions have been reached regarding this yield advantage which has
also been reported in studies from other states.
4. Weed Control
(James R. Martin)
Weed control issues that impact canola
production in Kentucky include managing problem weeds, herbicide carryover,
herbicide drift and volunteer canola.
Weed Management
Both the winter and summer complex
of weeds can cause problems in canola in Kentucky. Wild garlic bulblet
contamination reduces the market value of canola seed. Common chickweed,
yellow rocket and volunteer wheat can overcome canola during the fall or
late winter. Johnsongrass may cause harvesting problems in the spring,
particularly when canola stands are thin.
Currently there are no weed control
programs for a broad spectrum of weed species in canola, therefore, growers
must rely on practices that limit the introduction or spread of weeds.
Avoid weedy fields, especially those having a history of wild garlic problems.
Rotate to other crops in which effective weed control programs are available.
Wild garlic and other problem weeds may require more than one year rotation
to a crop such as wheat to significantly reduce a heavy infestation. Use
weed-free canola seed to prevent the introduction of wild mustard or other
weeds.
Preventative measures alone will not
eliminate all problems with weeds. Management practices such as early seeding,
tillage before planting and use of herbicides are sometimes necessary for
weed control in canola.
Seeding Early
Establishing canola early in the season
helps avoid competition from many weed species.
The most critical period for weed competition
to canola is during the first four to eight weeks after seeding. Canola
plants tend to grow slowly during this period and can be overcome by certain
weed species.
The peak period for emergence of such
weeds as common chickweed and henbit usually occurs from late September
through early November. Therefore, seeding in early September may give
canola the competitive edge over these weed species.
Seeding early does not necessarily
guarantee against problems from weeds. If stress factors such as lack of
moisture, poor seeding or herbicide injury inhibit crop growth, canola
seedlings may be overcome by weed competition.
Seeding early may also increase the
likelihood of canola plants recovering from winter injury and competing
against late emerging winter weed complex. Plants that are well established
by the onset of winter are likely to survive cold temperatures better and
generate new growth quicker than poorly developed plants.
Tillage Before Seeding
In some instances, a light discing
a few weeks prior to planting canola may stimulate seed germination of
some weed species. The weeds that emerge can then be destroyed by tillage
used for preparing the seedbed. This approach may be helpful in cases where
problems with volunteer wheat are anticipated.
The potential disadvantage of this
practice is that poor stands may occur in cases where tillage causes a
significant loss of soil moisture. Shallow discing of the upper two inches
of soil should be sufficient to encourage development of wheat and other
potential weeds and not dramatically affect the amount of soil moisture.
Chemical Weed Control
Treflan (trifluralin) is the only herbicide
currently registered for use in canola in Kentucky. Treflan is applied
and incorporated within the upper two to three inches of the soil profile
for pre-emergence control of grassy weeds such as cheat.
Canola tends to be shallow rooted during
early development and can be injured by Treflan. To ensure against injury
from Treflan read and follow label directions. The chance of canola injury
may increase when Treflan is applied above the recommended rate or when
seedling plants are stressed by soil that is dry or cool and wet.
Herbicide Carryover
The fact that canola is extremely sensitive
to many herbicides makes it a good candidate for injury from carryover
of herbicide residues in the soil. Developing long-term weed control plans
for rotational crops (up to 2 years or longer) may be necessary especially
for fields where persistent herbicides are used.
Fields treated with products containing
chlorimuron, atrazine or simazine may be more prone to having carryover
problems when soil pH is high. Hot spots that occur with overlaps of the
spray boom or non-uniform spread of herbicide impregnated fertilizers may
also lead to carryover problems to canola.
Listed in Table 4-A are herbicides
that have label restrictions that deal with rotation to canola.
Table 4-A. -- Herbicide Rotation Restrictions for Canola as a Rotational
Crop.
| Herbicide |
Restriction* |
Herbicide |
Restriction* |
| Accent |
10 months if pH << 6.5
18 months if pH > 6.5 |
Lorox Plus |
18 months and successful
field bioassay |
| Atrazine** |
2nd fall following application |
Pinnacle |
45 days |
| Beacon |
18 months |
Princep |
2nd fall following application |
| Canopy |
18 months and successful
field bioassay |
Pursuit |
26 months |
| Classic |
15 months and successful
field bioassay |
Reflex |
18 months |
| Command |
16 months |
Salute |
12 months |
| Commence |
16 months |
Scepter |
18 months |
| Devrinol |
12 months |
Sencor |
12 months |
| Dual |
18 months |
Squadron |
18 months |
| Harmony Extra |
60 days |
Tornado |
18 months |
| Lexone |
12 months |
Tri-scept |
18 months |
| Lorox |
4 months |
Turbo |
12 months |
*Minimum interval between herbicide application and seeding canola. Always
refer to herbicide label(s) for specific information.
** Additional products containing atrazine include Aatrex, Bicep, Buctril/Atrazine,
Bullet, Extrazine II, Laddok, Lariat, Marksman, and Sutazine+. Canola injury
from carryover of atrazine residues seldom occurs in Kentucky.
Risk of injury may be greatest when using atrazine at a high rate or
in fields with a high soil pH.
Herbicide Drift
Drift of herbicides from neighboring
fields may lead to canola injury. The growth-regulator-type herbicides
such as 2,4-D or Banvel can drift in the form of spray droplets or vapor
and injure canola. Canola appears to be most sensitive to these herbicides
during flowering.
Caution is needed when applying 2,4-D
or Banvel to wheat or corn fields or to fence rows near areas where canola
is flowering. Avoid spraying when wind gusts exceed five miles per hour.
Do not operate the spray boom at a height greater than recommended by the
nozzle manufacturer. Do not treat fields when temperature is expected to
exceed 85oF.
Canola -- A Weed in Rotational Crops
Seed loss that occurs with natural
shattering at plant maturity and from harvesting process appears to be
the major source of volunteer canola in rotational crops. Also, occasional
plants that occur along roads, in nearby fields or beneath powerlines are
believed to be from seed carried by leaking grain trucks, harvesting equipment
and birds.
Controlling the source of the spread
is the first step in dealing with canola as a weed. Timely harvest of canola
can reduce losses that occur with natural shattering or from bird feeding.
Sealing cracks in equipment and covering the grain bed of trucks can help
prevent seed loss when transporting grain between the field and the elevator.
Because canola is sensitive to many
herbicides, it is fairly easy to control in succeeding crops such as wheat
or double-cropped soybeans.
Buctril and Harmony Extra effectively
control canola in wheat if applications are made in the fall when canola
plants are small. The use of 2,4-D may be preferred for controlling larger
plants that have overwintered.
Although canola does not thrive well
during the hot summer months there have been instances where plants have
caused problems in no-till double-cropped soybeans. Potential problems
may occur from seedlings or regrowth of harvested plants. Many soybean
herbicides labeled for controlling wild mustard may also control canola.
5. Insect Pests
(Douglas W. Johnson)
Because canola has been grown in Europe
and Canada for a number of years, a significant body of literature deals
with insect pest problems of those areas. However, very little information
exists about insect pests of canola in the United States and virtually
none at all deals with the Ohio River Valley production area. As a result,
much current thinking about canola insect pests in Kentucky is derived
from observations, very recent experiments and opinions that can be reasonably
inferred from the existing literature.
As you read about insect pests, remember
that very few acres of canola are grown in Kentucky. Because the distribution
and concentration of food are major factors in insect population dynamics,
the insect pest complex will probably change as acreage increases or becomes
more concentrated. Traditionally, increased or more concentrated acres
have led to greater and more diverse insect problems.
Insects Present
The first entomological experiments
at Princeton, Kentucky were established to take a look at just what insects
might be found in Kentucky-grown canola. In general, this plant supports
a very large and diverse group of insects, including most of the insects
found on the Brassica crops (cabbage, mustards). Fortunately, most species
are parasites or predators of other insects and plant feeders of little
importance. However, at least three pests are of immediate concern, and
two species have a high probability of at least periodic concern. Additionally,
remember that this situation will change (probably increase) as acreage
increases.
Striped Flea Beetle (SFB)
Description
This insect is a close relative of
the tobacco and corn flea beetles but is much larger. The SFB is 1/8-inch
long and brown with two yellow stripes down the back. These insects have
the habit of quickly jumping away when disturbed. Infestation is limited
to the fall.
Damage
The striped and other flea beetles
use their chewing mouthparts to remove the upper surface of plant parts.
This leaves a scared appearance, but not a hole at the damaged location.
Canola, like soybeans, is most extensively damaged when this feeding occurs
on the cotyledon (seed leaves).
Threshold
No yield loss is likely to occur unless
plants die. There is no established number of SFBs, nor level of damage
to trigger treatment. However, as a guideline do not control unless: plants
are killed, the number of plants per square foot falls below the recommended
minimum and live feeding SFBs are still present.
"Canola" Aphids (CA)
A large number of aphid species are
found on canola (e.g. red turnip, cabbage, etc.). Currently, green peach
aphid is the most common aphid known to infest, debilitate and, under some
conditions, kill canola plants in Kentucky.
Description
Green peach aphids are small (1/16-inch),
tear drop shaped, soft bodied insects. They are usually found in colonies
on the underside of leaves. (Aphids are attracted to the color yellow,
so look at yellowing leaves first). Most aphids are wingless, though a
few have wings and these winged individuals (usually <<10% of the
colony) spread the infestation within and among fields. This particular
group of aphids contains both green and red (rusty brown) forms and looks
very much like the tobacco aphid.
Damage
Aphid problems usually occur in the
fall on small plants. However, scattered but very large infestations have
been observed in the spring, mainly on main stem pods. Aphids feed by sucking
plant juices through their piercing-sucking mouthparts. No noticeable physical
damage may be seen. Usually, when substantial damage occurs, the plant
takes on an unthrifty appearance, wilts or changes colors.
Warning: Canola may take on
a purple and or yellow color due to winter stress. Aphids are attracted
to yellow and may congregate on yellow leaves which are normally older,
lower on the plant and less thrifty. Aphids' presence on these leaves does
not necessarily indicate that the aphids caused the color.
Threshold
There is no established number of aphids
per plant nor percent infested plants that triggers a control situation.
However, control may be warranted if: infested plants show an unthrifty
appearance when compared to uninfested plants in a similar situation, a
large number of live aphids (one or more colonies per leaf) are present,
and the plant population is in danger of falling below the recommended
minimum per square foot.
Aphid populations are often very spotty.
In many cases border or spot applications provide very adequate control.
Cabbage Seed Pod Weevil (CSPW)
Kentucky has this pest in common with
many other canola production areas. CSPW is the most common target of about
15 state SLN labels across the United States and is also listed as a pest
in both Canadian and European literature.
Description
CSPW is a small weevil which feeds
on flowers and pods of canola and several other mustard plants. The beetle
is actually black but appears gray because of its body hairs. When wet,
it looks black. It has chewing mouthparts on the end of a long curved snout.
This snout is easy to see even though the insect is quite small.
The beetle is probably active on alternate hosts early in spring. CSPW
moves into canola at bloom and stays, feeding on the blooms (which does
no damage) and then laying eggs on the pods. The pod damage may affect
yields.
In the normal weevil fashion, an adult
female CSPW bites a hole in the surface of developing pods. It then turns
around and puts an egg into this cavity and once again turns around to
replace part of the plant material, thus covering the egg. The egg hatches
and a CSPW grub burrows its way into the pod's interior, where it feeds
on developing seeds until it matures. The final larval stage CSPW grubs
chew their way out of the pod, drop to the ground, pupate and emerge as
adults.
Damage
Damage results from grub feeding and
waste production inside the pod. No external sign of damage exists until
the pest has completed its life cycle and chewed its escape hole in the
pod wall. Normally, only one grub is in each pod and often only a portion
of the seeds in an infested pod are damaged.
Thresholds
This question is very difficult to
answer. Ward et al (1985) suggest implementing control when populations
reach two CSPW per plant. To examine the plant, observe it closely or tap
the main raceme over a tray.
Another method is to use a standard
15-inch insect sweep net. McCaffrey (1986) suggests that thresholds will
be very low (2-3/sweep) and that controls should be applied after full
bloom but before bloom ends.
Pests Resulting from Specific Conditions
Poorly Drained Soils
Several Kentucky producers have suffered
extreme loss in plant stands and at first the cause was unknown. This problem,
commonly known as Winter Decline Syndrome, could have several causes (Refer
to Diseases -- Stress Related Disease Complex for other causes). Water
saturated soils were a common factor in these cases and examination revealed
small fly maggots and pupae. Species identification has not been established,
but they are probably flies from the genus Delia. Delia radium (L.)
the cabbage root fly and D. platura (Meigen) the seed corn maggot
are likely culprits.
No thresholds or treatments are known.
Canadian research indicates that these pests are common and are not important
under good growing conditions. But under stress, especially water saturated
soils, this insect is extremely important with no rescue control available.
Drought
Drought contributes to a complicated
set of pest problems. Three conditions produce a perfect situation for
infestation by the false chinch bug: drought, canola production, and double
crop, no-till soybeans. The actual damage is to soybean seedlings but the
heavy residue left from canola production produces the environment. Drought
conditions favor false chinch bug development and slow soybean growth.
This combination has seriously damaged
soybeans in Kentucky. However, in all production years when one or more
of these factors were absent, no infestation occurred. It is very likely
that drought is the most important of these factors.
Treatment
It appears that application with an
insecticide with known soil activity gives the best results. Plants are
growing too slowly for systemic soil insecticides to have much effect and
are too small for treatment of only the plant. For best results, use a
broadcast spray with a lot of water, which saturates the canola residue,
forcing the false chinch bug to crawl through a layer of insecticide residue.
Insecticidal Treatments
Synthetic Chemicals
As of this writing, no chemical insecticides
have a national label for use on canola, but several states do have special
use labels. One chemical insecticide is labeled for use on canola in Kentucky:
Thiodan 3EC, which is a product of FMC Corporation (EPA SLN No. KY-890002).
This compound has a special local need
label (commonly called SLN or 24C) issued in 1989 for use in Kentucky.
To use this compound, you must have a copy of the SLN label in your possession
at the time of application.
Biological Controls
Microbial insecticides containing the
bacteria Bacillus thuringinsis (B.t.) may also be used. At present,
however, using B.t. does not help Kentucky's producers much because B.t.
compounds only affect caterpillar pests, which are not yet a problem on
canola. (Caterpillar pests are juveniles of butterflies and moths, e.g.,
diamond back moth and cabbage worm on cabbage.)
Summary and Recommendations
Several current and potential insect
pests exist on Kentucky-grown canola. The number of pests is likely to
increase as production increases and becomes established. There are no
insect pests currently or likely which would prevent the economic production
of canola in Kentucky although developing a comprehensive pest management
system will be important to economically protect this crop.
Producers should be aware that increasing
acreage, compacting distribution, continuous cropping history and use of
unrecommended fields and practices will likely increase insect pest significance.
To that end consider the following recommendations:
1.Plant only on recommended
(especially well-drained) soil.
2.Follow all recommended agronomic
practices to produce fields with vigorous plants and a stand of six or
more plants per square foot.
3.Rotate the field and locations
if possible on the farm. Try not to plant near other rape fields.
4.Control all volunteer rapes
and other Brassica sp. weeds (wild mustard, yellow rocket).
5.Scout the crop weekly and
more often as infestations arise.
6.Watch for insect pests in
following crops, especially soybeans.
7.Use only legal insecticides.
Remember that canola is a food for human consumption.
References
McCaffrey, J.P. Pest management of winter rape under dryland conditions.
Proc. 1986 PNW Winter Rapeseed Production Conf. Moscow, ID Feb. 24-26,
1986.
Ward, J.T., W.D. Bashford, J.H. Hawkins and J.M. Holliday. Oilseed
Rape. Farming Press Ltd. Ipswich, GB. 1985. 298 pp.
6. Diseases
(Donald E. Hershman)
Canola is susceptible to attack by
disease organisms any time from seeding through maturity. These organisms
originate from many sources including soil, infested or infected seed,
infested crop residue, or air-borne spores blown in from volunteer canola
plants, certain weeds, neighboring fields of canola, and related vegetable
crops or other crop plants.
Although canola has a short history
in Kentucky, many of the disease organisms that affect canola have been
here for a long time. We know this because these organisms also attack
other brassicas, both cultivated and weedy, and other common crop plants
in Kentucky. While many of these disease organisms are presently at low
levels, intensive cropping of canola may provide for their rapid build-up.
Then, given the proper environmental conditions, the development of serious
disease epidemics in the canola crop are possible. Crop failures due to
disease have already been documented for two pathogens.
Growers need to follow strict crop
management practices to reduce the chances of the development of serious
epidemics and to provide for the continued growth of the canola industry
in Kentucky. This section provides information on the biology and control
of the most serious or common canola diseases in Kentucky.
Major Diseases
The following canola diseases have
been documented in Kentucky and have great potential for causing serious
crop losses.
Sclerotinia Stem Rot (Sclerotinia sclerotiorum)
Importance
Sclerotinia stem rot (white
mold) is a serious problem of canola in many areas throughout the world.
The most severely affected areas are those which regularly experience extended
periods of wet weather while canola is in flower. Under heavy disease pressure,
yield losses of 50 percent or more are common. On average, percent yield
loss is equal to about half the percent of stems infected.
Severe episodes of the disease were
first confirmed in several areas of Kentucky in 1989. However, serious
losses due to stem rot are thought to have occurred as early as 1987.
Symptoms and Signs
Symptoms of stem rot appear in Kentucky
from May onwards. The disease is characterized by narrowly elliptical,
slightly sunken, light tan to gray lesions usually in the mid- to lower
stem. Hard, irregularly shaped (1/8- to 1/2-inch long x 1/8- to 1/4-inch
wide), black resting bodies of the fungus (sclerotia) are found within
the stem cavity of affected plants. Sclerotia may also develop on the outer
stems of plants under extremely humid/wet conditions and in the upper taproot.
Plants infected late in the season,
after most pods have developed, may lodge due to stem breakage but experience
few other yield effects. However, when plants are infected during the early
to mid-flowering stages, plants may have fewer pods, fewer seeds per pod
and smaller, shriveled seed. These plants ripen prematurely and suffer
severe lodging. Crop lodging greatly slows the harvesting process and increases
yield losses due to shattering.
Disease Development
Sclerotia fall to the ground during
harvest or as stems break when lodging occurs. From mid-April to mid-May,
sclerotia in the upper one to two inches of soil germinate to produce small
golf tee-shaped structures called apothecia. Sclerotia buried deep in the
soil remain dormant (8 years or longer) until brought near the surface
by cultivation. A single sclerotium can produce from one to 15 apothecia.
Apothecial formation on individual
sclerotia can occur all at once or over a period of weeks; the process
requires that soil moisture levels be high and temperatures low to moderate
for at least 10 consecutive days. Both cooler temperatures and adequate
soil moisture are favored within dense, vigorously-growing canola stands
and within thinner stands with heavy weed pressure. Canopy density also
affects the length of time that individual apothecia remain active.
Apothecia release spores (ascospores)
during wet weather and periods of heavy dew. The spores are blown to and
infect flower petals of canola plants. Ascospores can be blown into a crop
from a relatively distant source, however, the most important source of
stem rot inoculum comes from within a field or from immediately adjacent
fields and areas. Infected, fallen petals that lodge on leaf surfaces,
in leaf axils and on plant stems then serve as sites where the fungus moves
into the main stems of plants during wet or humid conditions. Ascospores
are unable to infect canola plants directly. Conversely, direct infection
of stems as a result of sclerotial germination, without apothecia or ascospores
being produced, has been documented in more southern production areas.
Once plants are infected, symptoms of stem rot appear after about 10 to
14 days.
Control
All canola varieties are susceptible
to Sclerotinia stem rot. Apparent differences in susceptibility
are related to varying temperature and moisture conditions during the different
flowering periods for the varieties and not to disease resistance mechanisms.
The control of Sclerotinia stem
rot in Kentucky is difficult for a variety of reasons. The most notable
of these is the wide distribution of the causal fungus and the frequent
occurrence of conditions favorable to stem rot during the period that canola
varieties flower in Kentucky. Because of this, the moderation of stem rot
problems is only possible when growers are consistent in the implementation
of a specific set of management practices. The use of any single measure
frequently results in unacceptable levels of stem rot in production fields.
•Not growing canola or other stem rot
susceptible crops in a field or nearby fields more frequently than one
in five years helps limit the build-up of the stem rot fungus where low
levels of the fungus currently exist. The stem rot fungus can infect 145
plant genera and literally hundreds of species. As a result, selection
of an acceptable non-host crop is very important. In Kentucky, wheat, barley,
corn, milo and other grass crops are good choices. Soybeans, while susceptible
to stem rot, rarely develop the disease in Kentucky because late spring
and summer conditions are usually not supportive of disease development.
Thus, soybeans appear to be an acceptable non-host crop in canola production
areas in Kentucky.
•The value of crop rotation is greatly
diminished where high pathogen levels are being maintained in and around
fields infested with stem rot susceptible weed hosts such as field pennycress,
shepherd's purse, wild mustard and related species. In these situations,
crop rotation of canola must be coupled with the use of cropping systems
and weed management practices, in off-canola years, which limit the development
of stem rot susceptible weeds. Even where these practices are strictly
followed, the danger of a serious stem rot problem still exists due to
the possible movement of spores from adjacent farms where these practices
are not followed and from nearby tree lines, fence rows, pastures and fallow
areas which are heavily infested with weeds susceptible to stem rot. This
is much less of a factor the further away poorly managed farms and non-crop
areas are from properly managed canola fields. This is due to the fact
that most spores which cause severe stem rot problems come from within
or nearby the field, rather than from significantly distant sources.