ID-125
Wheat is best adapted on well-drained soils. Since wheat does not tolerate waterlogged conditions well, yields and stands are reduced in fields prone to standing water, flooding, or poor drainage. Wheat can be grown successfully on moderately and somewhat poorly drained soils, but the long-term yields are usually reduced by five to ten bushels per acre due to stress placed on the wheat during wet springs, increased winterkill, higher nitrogen losses, inability to access fields with application equipment, etc. During springs with normal or below normal rainfall, yields on these soils approach those on well-drained soils.
Economically and agronomically, it is difficult to justify planting wheat without crop rotation. There are several benefits for growing wheat in rotation with other crops. Yields are increased, and disease, insect, and weed problems are reduced.
Wheat fits well into cropping systems and rotations in Kentucky. It is planted in the fall after summer annual crops are harvested and can be harvested early enough in the summer for a second crop to be planted (double-cropped). Double-cropping is an important economic component of the wheat enterprise in Kentucky. More than 85 percent of the harvested wheat acreage is double-cropped, primarily with soybeans. Most of the wheat harvested for grain is grown in a cropping system of three crops in two years (corn/wheat/double-crop soybeans).
Careful selection of wheat varieties is one of the most critical decisions the wheat producer will make. This key decision is complicated by such factors as the need for resistance to several diseases; the double-cropping system, which requires early maturity; and the extreme year-to-year climatic variation in Kentucky. Collecting, summarizing, and studying variety performance data are the first steps in making this decision. Summarize all available information on varieties from university and agribusiness trials. The University of Kentucky Small Grain Variety Trials provide the most information on many varieties tested under a range of environments. Results of the variety trials are published each year in progress reports and are available at your local Cooperative Extension Service office. When selecting varieties to grow, consider proper maturity, sufficient winterhardiness, lodging potential, disease and insect resistance, test weight, and high yield potential.
With regard to proper maturity, select a combination of early to late varieties that allows you to spread out harvest time and permit timely harvest of each variety and reduce the risk of environmental stress. Extremely early varieties have an increased risk of damage by a late spring frost, while very late varieties are more affected by dry, hot weather and may mature too late for successful double-cropping.
In Kentucky, winterhardiness might only be a problem every three or four years. However, many varieties developed in the more southern states might not have as much winterhardiness as varieties developed in more northern areas.
Genetic resistance to diseases and insects is the most cost effective means of limiting damage from pests. However, no single variety is resistant to all diseases and insects. Therefore, it is important to determine which labeled fungicides and insecticides are available when genetic resistance is not.
It is important to consider test weight, in addition to yield potential, when selecting a wheat variety. Test weights below 58 pounds per bushel result in severe discounts, which erode profitability.
Consider yield figures from data accumulated over a range of conditions and years. Wheat yield is the product of three components: heads per acre, kernels per head, and weight per kernel. No single management practice optimizes all of these yield components. To maximize these yield components, you have to control all of the factors involved in intensive wheat management (except weather).
Once you have selected the varieties, the best guarantee of obtaining the quality seed necessary for highest yields is to use certified seed or seed of proven high quality from an established, reputable dealer.
Planting precision is a crucial step in producing a successful wheat crop. The objective when planting wheat is to establish a uniform stand of at least 25 plants per square foot with adequate fall growth for tiller development and an established root system for winter survival. Planting practices include seedbed preparation or no-tillage planting (see Section 4—Planting Methods), planting date, seed placement, seeding rate, row width, and use of tramlines.
The recommended planting date for wheat is a compromise between early planting to ensure adequate fall growth and winter survival and later planting to decrease disease and insect infestations. Although the planting date is often dictated by weather or harvest of a previous crop, you should plant wheat about one week before to one week after the expected date of the first fall frost. The optimum planting date period for most of Kentucky is October 10 through October 30. Soil temperatures are usually high enough during this window for the crop to emerge in seven to ten days or less. Also, the length of time between the first frost and winter dormancy for growth is critical for the development of an adequate number of tillers. Tillers developed in the fall are essential to producing high yields. A longer period of growth in the spring and more extensive root systems mean that fall tillers account for most of the grain produced in an intensively managed crop.
Late-planted wheat misses much of the critical fall growing period, generally suffers more winter damage, is more prone to heaving (uplifting of the plant and root system due to alternate freezing and thawing of soil), tillers less, has reduced yields, and matures later than wheat planted at the recommended time. It is difficult, if not impossible, to make up for late planting by management practices employed at later growth stages.
Planting too early, on the other hand, can result in excessive fall growth and create the potential for more winter injury (growth stages too advanced), greater risk of spring freeze injury, fall disease infection, and increased problems with aphid (barley yellow dwarf) and Hessian fly infestations. Delaying planting until October 10 (in northern Kentucky) or October 15 (in southern Kentucky) generally averts Hessian fly damage. These dates are known as the fly-free planting dates.
Final stand and potential yield of a wheat crop start with proper seed placement. Plant seeds 1 to 1½ inches deep when soil moisture levels are adequate, slightly deeper if moisture is deficient. Rapid emergence and good root development start with good seed-soil contact.
Many wheat varieties have small seed, and when seed is planted deeper than 2 inches, emergence is delayed. Some semi-dwarf varieties with short coleoptiles might open the first leaf below ground and die. Deep seed placement delays emergence (delayed planting effect) and reduces stand, and emerged plants have less vigor, less initial vegetative growth, and reduced tillering.
The other problem is not planting seed deep enough. Planting seed less than ½ inch deep can result in uneven germination and emergence because of dry soil. Shallow seed placement also can result in more winter injury and greater susceptibility to heaving.
Seed placement is critical in no-till planting: seed must be placed in the soil at the proper depth and below all the mulch. It is important to distribute the mulch evenly on the soil surface so that you get a good cut through it for proper seed placement. Poor seed placement is a major problem in no-tillage planting. Fast, uniform seedling emergence provides quick ground cover and erosion protection.
Wheat seed size varies dramatically among varieties and can be influenced by production environment and degree of conditioning. Using seeding rates expressed in terms of volume or weight (bushels or pounds) per acrewithout consideration of seed sizecan result in stands that are too low or too high. Proper stand establishment requires that the seeding rate be determined in terms of number of seeds per unit area (per square foot or linear row foot). Seeding rates below optimum may reduce yield potential, while excessive seeding rates increase lodging, create a greater potential for disease, and increase seed costs. The optimum planting rate is 35 seeds per square foot with an objective of obtaining at least 25 plants per square foot. For precise seeding, calibrate your grain drills because seeding rate charts on drills may not be precisely accurate and size and shape of seed can affect seed delivery. A five-step procedure for proper grain-drill calibration follows:
Step 1. Optimum seeding rates per drill-row foot vary depending on row width, date of planting, and expected yield. Fields in which yields are not expected to be above 45 to 50 bushels per acre require only 30 seeds per square foot. Use Table 3-1 as a guide for seeding rates at various row widths when the seed germination test is 90 percent or higher. The linear length of row needed to drill 30 to 35 seeds per square foot for a certain row width is calculated by dividing 144 square inches (1 square foot) by the drill row width.
| Table 3-1. Recommended number of wheat seeds to plant per square foot or per drill-row foot. | |||
Row width (inches) |
Length of row needed for 1 sq ft (inches) | Seeds/row foot needed a | |
| 30 seeds per sq ft | 35 seeds per sq ft | ||
| 4 | 36.0 | 10 | 12 |
| 6 | 24.0 | 15 | 18 |
| 7 | 20.6 | 17 | 20 |
| 8 | 18.0 | 20 | 23 |
| 10 | 14.4 | 25 | 29 |
| a If planting time is delayed, increase seeding rates by two to three seeds/sq ft (one to two seeds/row foot) for every two-week delay beyond the optimum planting date. | |||
For seed that has less than 90 percent germination, seeding rates should be increased. Seeding rate adjustments for germination can be calculated by dividing the desired seeding rate (seed per square foot or pounds per acre) by the percent germination. For example, a desired seeding rate of 35 viable seeds per square foot with a seed germination of 80 percent would require a seeding rate of 44 seeds per square foot (35 ÷ .8 = 43.75).
Table 3-2 gives estimates of the pounds of seed needed per acre at seeding rates of 30 and 35 seeds per square foot for a known seed size.
| Table 3-2. Number of pounds of wheat seed needed, depending on seed size and seeding rate. | ||
Seeds/pound | Seeds/square foot a | |
| 30 | 35 | |
| lbs/acre | ||
| 10,000 | 131 | 152 |
| 12,000 | 109 | 127 |
| 14,000 | 93 | 109 |
| 16,000 | 82 | 95 |
| 18,000 | 73 | 85 |
| 20,000 | 65 | 76 |
| a Based on 90 percent or greater germination. | ||
Step 2. Calculate the number of seeds required in 50 drill-row feet. For example, with 7-inch wide rows and on-time planting, an appropriate seeding rate would be 20 seeds per drill-row foot multiplied by 50 feet, which equals 1,000 seeds planted every 50 feet of row. Count 1,000 seeds of each variety and put them in a graduated tube, such as a rain gauge, or other clear tube or cylinder. Mark the level of the 1,000 seeds in the tube.
Step 3. Hook a tractor to the grain drill so that the drive wheels of the drill can be raised off the ground and the drive gears can be engaged. Jack up the drive wheel so it clears the ground and turn the wheel several revolutions to be certain all working parts are turning freely. Check all drill spouts for blockages.
Step 4. Determine the number of revolutions the drive wheel must make to travel 50 feet. Measure the distance around the drive wheel. This distance can be measured directly with a tape measure or calculated by measuring the diameter or distance across the tire and multiplying that distance by a factor of 3.2. For example, if the drive wheel measures 30 inches from tread to tread (diameter), the distance around the tire should measure 96 inches (30 x 3.2). The number of tire revolutions per 50 feet (50 x 12 inches) equals 600 inches. Divide 600 inches by 96 inches to get 6.25 revolutions of the tire per 50 feet of travel. Make a mark on the wheel so the number of revolutions can be conveniently determined when the wheel is turned.
Step 5. Calibrate the drill.
a. Put at least a quart of seed of the variety to be calibrated over at least two drill spouts. (You get better accuracy if you use more than one drill spout.)
b. Set the drill on a rate setting expected to be close to that desired, and turn the wheel the number of revolutions needed for 50 feet (as determined in step 4) while catching the seed from each spout in a separate container. Pour the seed caught into the precalibrated tube (as determined in step 2), and check the level. Repeat for each of the drill spouts.
c. Change settings as needed, and repeat until you get the appropriate number of seeds (level marked on the tube). Repeat the above steps for each variety.
Option:The above procedure also can be used in the field under actual field conditions by catching seed while the drill is traveling a distance of 50 feet.
Research throughout the growing region of soft red winter wheat has shown 5 percent to 10 percent higher yields when wheat is planted in 4-inch rows versus 8-inch rows. Likewise, research has shown significant yield decreases for wheat grown in row spacings greater than 10 inches. Wheat must be planted at a uniform rate and depth, and conservation requirements must be met. Remember that 4-inch-row drills can clog due to excessive surface residue or clods. Decide if the expense of purchasing a narrow-row drill can be repaid by yield increases. Choose a drill with as narrow a row width as possible after considering the total crop rotation, tillage system used, and conservation compliance requirements for your farm.
Using tramlinesroadways placed in the wheat field at plantingis one of the best management tools you can employ to accomplish precision application of nutrients, pesticides, and/or a growth regulator. These roadways should match the width of the applicator tractor tires and be spaced to match the width of the spray boom and fertilizer applicator. In other words, the distance from center to center of the tramlines should be the same width as the application equipment. The advantage of using tramlines instead of driving over the wheat plants after jointing is that the plants beside the tramlines make some yield compensation for the unplanted area, whereas there is no compensation from plants that have been run over. Tramlines allow timely application of inputs and more uniform applications of nutrients and pesticides with no skips or overlaps.
Tramlines are formed by blocking drill spouts that correspond to the width of the tracks of the sprayer tractor (Figure 3-1). Using tractors with narrow tires so only one drill row needs to be blocked is a recommended practice. Devices that automatically close the selected drill spouts on the appropriate planting pass through the field are available for most grain drills. Fertilizer and spray booms should be at least 40 feet wide to be economical. The distance from the first tramline to the edge of the field should be one-half the width of the sprayer.
Figure 3-1. An illustration of a tramline system matching drill passes and sprayer boom width.
Option: You can also form tramlines somewhat similar to the roadways (skip rows) established at planting without the investment of shut-off attachments on the drill. Do this by running over the same tracks each time an application is made. For best results, use the same track for each application and do the first track (application) early enough to allow compensation from plants in adjacent rows.
Wheat is subjected to adverse weather conditions during much of its growth period. As long as wheat is seeded in the fall close to the recommended planting dates, you can expect little freeze damage in the fall. Autumn frosts and cool temperatures actually help by hardening plants for the months of cold winter weather ahead. Expect winterkill on poorly drained soils, with extreme temperature fluctuations, where poor fall root development occurred, and with sustained low temperatures (particularly with no snow cover). Extremely cold winters tend to cause more winterkill in varieties developed in more southerly locations because they have less winterhardiness. Heaving is a major cause of late winter or early spring damage to small plants due to extreme temperature fluctuations, especially on poorly drained soils.
Spring freeze injury can occur when low temperatures coincide with sensitive plant growth stages. Injury can occur across large areas of the field but usually is most severe in low areas or depressions in the field where cold air settles. The risk of spring freeze injury is greater when wheat initiates spring growth early due to higher than average temperatures and advances through its developmental stages more quickly than normal or when an unusually late freeze occurs after the wheat is further advanced. A late spring freeze can reduce yield because of damage to the head and stem. Head and stem damage usually is not visible for a week to ten days after the freeze. The stem will likely be damaged close to the ground. Weakened stems will likely break over or lodge as the plant matures. To check for damage to an unemerged head, cut into the stem to find the growing point (developing head). An undamaged spike (or head) normally appears light green, glossy, and turgid, whereas a killed head is pale white or tan, limp, shrunken, and not developing in size. Growing tissue of plants that have been frozen is dry, bleached, and shrunken. Table 3-3 gives a summary of injury-causing temperatures, symptoms, and yield effects of freeze injury at various stages of growth (see Supplemental section, p. 51 for pictures of freeze damage).
| Table 3-3. Freeze injury in wheat. | |||
Growth stage | Approximate injurious temp. (two hours) | Primary symptoms | Yield effect |
| Tillering (1-5)a | 12°F | Leaf chlorosis; burning of leaf tips; silage odor; blue cast to fields | Slight to moderate |
| Jointing (6-7) | 24°F | Death of growing point; leaf yellowing or burning; lesions, splitting, or bending of lower stem; odor | Moderate to severe |
| Boot (10) | 28°F | Floret sterility; spike trapped in boot; damage to lower stem; leaf discoloration; odor | Moderate to severe |
| Heading (10.1-.5) | 30°F | Floret sterility; white awns or white spikes; damage to lower stem; leaf discoloration | Severe |
| Flowering (10.51-.54) | 30°F | Floret sterility; white awns or white spikes; damage to lower stem; leaf discoloration | Severe |
| Milk (11.1) | 28°F | White awns or white spikes; damage to lower stems; leaf discoloration; shrunken, roughened, or discolored kernels | Moderate to severe |
| Dough (11.2) | 28°F | Shriveled, discolored kernels; poor germination | Slight to moderate |
| a Numbers in parentheses refer to the Feekes scale (see page 7). | |||
After the wheat has emerged, make a stand count to determine if your target population was achieved and if the final stand is acceptable to achieve the maximum yield potential. Make fall stand counts after all potential plants have emerged (one to two weeks after emergence). Make spring stand counts before greenup of the plants occurs to determine if winter damage has reduced the initial plant population obtained in the fall. Count only whole plants, not tillers. Fields with stand counts below 15 plants per square foot have less than 75 percent yield potential (Table 3-4) and probably should not be kept but used instead for planting corn or soybeans. If stand counts are adequate to keep but somewhat reduced from optimum, consider early nitrogen application. To determine the number of plants per square foot, use the following steps:
Step 1. Use a yardstick, or cut a dowel rod to a 3-foot length.
Step 2. Place the measuring stick next to an average-looking row, and count all plants in the 3-foot length of the row. Record the number.
Step 3. Repeat the counting process in at least five other locations well spaced around the field. Record all numbers.
Step 4. Average all of the plant stand counts from the field.
Step 5. Calculate plants per square foot with the following equation:
plant number = (average plant count × 4)/row width in inches
| Table 3-4. Wheat yield potential based on plants per square foot. | ||
| % Stand | Plants/sq ft a | % Yield potential b |
| 100 | 30-35 | 100 |
| 80 | 24-28 | 100 |
| 60 | 18-21 | 90-95 |
| 50 | 15-18 | 75-80 |
| 40 | 12-14 | 60-70 |
| 20 | 6-7 | 40-50 |
| a Multiply by 9 for plants/sq yd.
b This provides an estimate of the relationship of wheat stand to yield potential and is only a guide. Many factors (plant vigor, weather, disease, fertility management, planting date, and variety) influence how a wheat stand ultimately responds to achieve its final yield potential. | ||
Taking a tiller count (count includes main shoot and tillers) at Feekes 3 is the first step in all fields for determining nitrogen needs in late winter or early spring. Tiller counts below 70 per square foot indicate the need for nitrogen at Feekes 3. At recommended populations, many plants will have only three to four stems (main shoot plus two to three tillers). Thus, 70 to 100-plus tillers (stems) per square foot at Feekes 3 is considered adequate. To determine the number of tillers at Feekes 3, count all stems with three or more leaves.
You also should take head counts late in the season (Feekes 10.5 or later). A harvest objective for maximum yields should be 60 to 70 heads per square foot (600 per square yard) with 35 kernels per head (16 to 18 spikelets per head). For adequate yields, 55 heads per square foot (500 per square yard) are needed. If the number of heads per square foot is too high (90 to 100), severe lodging can occur and seeding rates were probably too high. Use the same procedure to count tillers or heads as outlined above for plant populations.
Lodging can be a problem when poor wheat management practices are utilized or very high yields are expected. Lodged wheat can result in decreased combine speed because of the amount of straw that must be processed through the combine, decreased grain recovery, delayed harvesting after rainfall and heavy dew, and more difficult planting conditions for double-crop soybeans that follow wheat. With proper management, the potential for lodging is lower today than in the past. Proper variety selection, nitrogen management, and seeding rates and a balanced fertility program reduce the potential for lodging. Situations do occur, however, in which there is a large carryover of residual soil nitrogen or weather conditions produce very lush crops and the potential for lodging is high.
When the potential for lodging is high, consider using the growth regulator Cerone. It is currently the only
labeled product for lodging control in wheat. Cerone prevents lodging by shortening the wheat plant and strengthening
the straw. It does not increase yields if no lodging occurs. Correct application is critical and should be made
between Feekes 8 and 10. Never apply Cerone to crops with exposed heads. Research at the University of Kentucky
showed best results when Cerone was applied at Feekes 8 or 9. Carefully read the label, and follow all directions.