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What is going on with
Darke County’s soybeans?
by Justin Petrosino, ANR Extension Educator
OSU Extension, Darke County
With
the last few rains the soybeans in Darke County are starting to look
better. With the hot and dry temperatures some fields are showing
symptoms caused by underlying conditions. With the rainfall these
symptoms should subside. Diseases do remain a concern in some fields
that were inundated with rain but overall the crop is weathering the
heat.
Quite a few fields in the county are looking a little yellow or even
white in isolated pockets. There are two main causes for these
conditions. The first is the application of glyphosate products. If a
spray rig is slowing down or happens to overlap soybeans can get a
double dose of glyphosate. Although the beans are Roundup Ready they
can still show signs of soybean flash. This condition is caused by a
product of the breakdown of glyphosate in the plant. The compound,
AMNP, actually destroys chlorophyll causing the yellowing and bleaching
of leaves. The condition typically affects only a small portion of the
field so yieldloss is not a concern. The condition is not caused by
glyphosate binding micronutrients in the plant so any foliar
applications will not help the condition. A few fields in the county
are showing intervenal chlorosis in small pockets. When ground is
worked and beans are planted in sub-optimal conditions root growth can
be inhibited by compaction. Beans don’t form as many nodules for
nitrogen production and in dry conditions the uptake of other nutrients
is inhibited by poor root growth. Any stress compounded on the drought
and compaction stress, like an herbicide application, can exacerbate
the problem. Thankfully the rains of this past week and weekend will
help alleviate any yellowing.
In
the world of insects soybeans are faring well. Aphids are either absent
or in very low numbers in the field. No fields have surpassed the
economic threshold of 250 aphids per plant, even in northern Ohio.
Timely rains have reduced the risk of spidermites becoming an issue.
Foliar feeding is present in most fields but defoliation must be above
25% in beans in full bloom for an insecticide application to be
warranted.
With
weeds all I can say is marestail, marestail, marestail, and volunteer
corn! There is very little to do for marestail postemergence other than
try to decrease seed production with an application of glyphosate and
an ALS inhibitor like FirstRate, Synchrony, or Classic. If Liberty Link
beans are planted Ignite can be an option on marestail below 4 inches
in height. The only surefire way to control marestail is a strong
burndown that includes an herbicide with residual activity on
marestail. Postemergence applications are not an option. Corn can be
controlled with any grass control product labeled for soybeans.
Diseases in both corn and soybeans are typically not a concern in hot
dry weather. Most diseases stop any growth once temperatures climb
above the mid 80s. If diseases are present in hot weather fungicide
applications are not recommended. An application to rolled corn and
cupped soybean leaves yields poor coverage by the fungicide and results
in inadequate control. Also, most diseases impacting soybeans at this
time, including Phytopthora, sudden death syndrome (SDS), and brown
stem rot cannot be controlled with a foliar application of a fungicide.
The only economic diseases of soybeans to be controlled by a fungicide
application are white mold and frogeye leaf spot. To control white mold
fungicide applications should be made at flowering when warm and rainy
conditions persist through flowering and a susceptible variety is
planted. Frogeye leaf spot should be controlled when it is detected at
economic levels on the leaf if a susceptible variety is planted.
For
more information on soybean management, specifically soybean disease
management OSU has two great options. The first option is the newly
revamped Plant Pathology website at http://oardc.osu.edu/ohiofieldcropdisease/.
If you prefer a more interactive discussion the West Ohio Agronomy
Field Day at the Darke County Farm on August 2, 2011, is your best
option. Dr. Anne Dorrance, OARDC Soybean Plant Pathologist, will be
speaking at the event on soybean disease management. To register for
the field day or for more information call the OSU Extension Darke
County Office at (937) 548-5215.
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