|
It is very likely that
Hurricane Katrina moved spores of the soybean rust fungus into the state as it
passed though this past week. But, even though spores are likely to be in
Kentucky, the overall concentration of spores will be low and dilute.
Don Hershman,
UK Extension Plant Pathologist |
By Laura Skillman
PRINCETON, KY., (Sept. 9, 2005) – The majority of Kentucky’s soybean crop looks
to have escaped Asian soybean rust damage this year.
Soybean rust continues to be confined to the deep southern United States,
primarily in southern Alabama, Georgia and Florida, said Don Hershman, plant
pathologist with the University of Kentucky College of Agriculture.
It is very likely that Hurricane Katrina moved spores of the soybean rust fungus
into the state as it passed though this past week. But, even though spores are
likely to be in Kentucky, the overall concentration of spores will be low and
dilute, he said.
“There simply is not enough acreage of soybean or kudzu affected by rust in the
Deep South to result in large numbers of spores blowing into any field in
Kentucky,” Hershman said. “And, for the spores that do blow in, it will take
four to six weeks before the disease will be to the point where significant
damage is possible, resulting from defoliation.”
That means if Katrina brought in a reasonable number of spores, it will be at
least the end of September or early October before any damage will be possible.
By that time, most soybean fields in the state will be close to or at
physiological maturity.
“In other words, soybeans that will be near, at or beyond physiological maturity
by the end of September are home free for 2005,” he said.
Fields that will not reach physiological maturity until mid-October or later,
primarily soybeans planted following the wheat harvest, still may be at risk.
However, even in those cases, fields will not go from being clean to having a
lot of rust overnight, Hershman said. There will be plenty of time to react,
should spraying be required, and there will be indications that the soybean rust
risk is high, based on the disease being found close to or even in Kentucky.
Spraying would only be advised in later soybean crops if the risk is high, and
there is still more than a month to go before the crop will be at R6, the full
seed growth stage. Fungicides should not be applied once a crop is at the R6
stage. In fact, most fungicide labels prohibit spraying soybeans that have
reached the R6 stage.
“In my opinion, it is very unlikely that any more than a handful of fields may
need to be sprayed for rust this year,” Hershman said. “It is highly possible
that no fields will need to be sprayed. Overall, in my opinion, the prognosis is
quite good that soybean rust will cause little or no damage to the 2005 Kentucky
soybean crop.”
From a scouting perspective when one pod on the main stem has lost its green
color, the entire plant is at or very close to physiological maturity, said Chad
Lee, UK Extension plant and soil scientist. This means that all dry weight
(yield) has been accumulated and soybean rust will no longer hurt yields.
Hershman and Lee noted that by mid-October frost may play a bigger role in the
development of late planted soybeans. Frost will stop the development of
soybeans along with rust, Lee noted. So, if in mid-October rusts hits the state
but there’s also a good chance of frost within a couple of weeks, farmers will
have to decide if spraying for rust will be justified.
County Extension offices have charts available that show the likelihood of frost
within the state. Frost dates vary somewhat by location.
Writer: Laura Skillman
270-365-7541 ext. 278
Contact: Don Hershman,
270-365-7541 ext. 215
Chad
Lee, 859-257-3203
Return to Main News page. |
