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Extension Entomology

Category: Soybean

Soybean Update

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

(thistle caterpillars, painted lady/thistle caterpillar chrysalis, garden webworm, bean leaf beetle, false chinch bug)

Soybeans seem to be the crop getting the most attention throughout north central Kansas.  Thistle caterpillars have been pupating in their unique little chrysalis that can be lime green to brownish in color and is often found hanging on the underside of leaves within the soybean canopy.

 

Some fields, especially in areas north of I-70 Highway, have many thousands of these painted lady butterflies flying around, often focused around the borders of soybean fields.  These fields are where the thistle caterpillars have been feeding and pupating.  The orange, black, and white spotted butterflies will be depositing eggs in soybeans, sunflowers, and many different weed species and the small spiny larvae will then begin feeding.  So, sampling in soybeans and sunflowers should continue for about the next three weeks.

 

 

 

Webworm larvae are feeding on soybean leaves and bean leaf beetle adults are starting to emerge and both are adding to overall defoliation in soybeans.  For management decisions regarding soybean defoliators, please refer to the KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

 

 

 

False Chinch bugs have also been reported from soybeans.  These bugs are often mistaken for chinch bugs, hence the name, but unlike chinch bugs, they will sometimes feed on soybeans after their natural weed hosts are killed.  However, this feeding is usually of little consequence.  Although these bugs often congregate by the hundreds and thousands, they usually disperse within a few days with no tell-tell signs that these huge numbers were ever there.

 

 

Soybean Update

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Spider mites are infesting soybeans relatively early this year in several areas in north central Kansas.  These mites damage plants by feeding on individual plant cells, usually starting on the undersides of lower leaves.  Under less than ideal growing conditions, these mites can turn leaves brown and cause them to die in a few days.  Mite populations can build up quickly and if treatment does become justified please use enough carrier to penetrate into the canopy and reach the undersides of leaves.  Also, realize that if using an insecticide to control other pests, the predators will likely be significantly reduced which may allow mite populations to increase.   For more information on spider mite management, please see the Corn Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF810.pdf

 

 

Soybean Update

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Adult bean leaf beetles are present, but scarce, in soybean fields in north central Kansas as of 20 July.  This indicates that the majority of the population is in the larval stage, feeding on soybean roots, and/or is pupating in the soil.  There are also some garden webworms and a few painted lady, or thistle caterpillars, in some fields, but not enough to be of concern.

 

 

For more information on treatment thresholds and management options, please see the Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

Japanese Beetles

Posted on by Sharon Schroll

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

Adult Japanese beetles have been detected around north central Kansas in the last 7-10 days.  These adults may feed on corn, sorghum, and soybean leaves, as far as field crops are concerned, and may cause some “window paneing” much like the leaf feeding of adult corn rootworms.  However, this leaf feeding usually is of little consequence.  In corn, these beetles will be attracted to the silks and, as they can be very veracious feeders, may clip these silks at a pretty good rate.  Fortunately, they are usually localized to small “hot spots” in some fields and thus do not really justify any insecticide application.  These adult Japanese beetles may be active for another couple of weeks, after which only eggs and larvae will be present, and these life stages are not a threat to these crops.

 

Bean Leaf Beetles in Soybeans

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Soybeans seem to be growing really well around north central Kansas.  As these plants start germinating and growing, however, they provide very attractive hosts for bean leaf beetles.

 

These soybean pests have been inhabiting alfalfa fields and grassy areas since last fall, waiting for these first soybeans.  They are very efficient at finding young, succulent soybeans when the plants start emerging.  They are also relatively unique as foliage feeders because they usually chew round and/or oblong holes in the leaves.

These beetles can eat an alarming number of holes in these small plants.  However, the young plants are very resilient at overcoming this leaf feeding and so there is normally very little impact on yield.  For more information on bean leaf beetle biology, treatment thresholds, and management options please see the following:

Bean Leaf Beetles: https://www.bookstore.ksre.ksu.edu/pubs/MF2824.pdf

Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

 

Soybean Pest Update

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Many beans have passed the stage that is attractive for bean leaf beetle adult pod feeding.  However, later planted beans are still tender enough to attract these beetles and they are feeding on the pods.

blb-adult

blb-pod-damage

 

This can reduce yield quickly so monitoring needs to continue until the last pods have turned yellow.  Please refer to the 2016 Soybean Insect Management Guide available at: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf for management recommendations.

Soybean Pest Update

Posted on by Sharon Schroll

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

Green Cloverworms in Soybeans

Remember a few weeks ago when there was considerable concern relative to all the green cloverworms causing irregular holes in leaves? Even skeletonizing some areas of some fields until treated with an insecticide and/or and entomopathogenic fungus started decimating the larval populations?   Well, the surviving larvae pupated and now are annoying little aerodynamically shaped dark brown moths flying around lights at night or trying to get in through doors and windows.

gcw-close

gcw-defol

gcw-fungus

gcw-adult

These moths will mate and then begin ovipositing in soybean and/or alfalfa fields.  Eggs hatch in approximately 10-14 days and the larvae will again start feeding on leaves of either crop.  By this time of year, the larval feeding is usually of little consequence relative to yield.  However, really late planted soybeans, and all alfalfa fields, should be closely monitored to ensure leaf feeding in either crop does not affect pod fill in soybeans or leaf area in alfalfa.

 

Soybean Podworms

These insect pests seem to be on about the same developmental schedule as green cloverworms.  So, late planted soybeans may be at risk for bean feeding within the pods.

cew-adult

cew-pod-damage

 

Adult bean leaf beetles, while probably not as numerous as in past years, may still be feeding on the pods themselves.  This can cause yield reductions.  For more information on bean leaf beetle biology and control, please visit: https://www.bookstore.ksre.ksu.edu/pubs/MF2824.pdf

blb-adult

blb-feeding-pod

Woollybear Larvae

Another leaf feeder that can cause concern this time of year is woollybear caterpillars.  There are several different species but all are foliage feeders although they rarely cause any economic problems.

woollybear-white

woollybear-orange

 

Stink Bugs

Hopefully, most soybeans are past the stages that are succulent enough for stink bugs to be feeding on.  However, there are still some late planted beans setting pods with seeds that may be vulnerable to stink bug feeding.  So, until pods are turning yellow or brown, fields probably should continue to be monitored for soybean podworms, adult bean leaf beetles, and stink bugs.

green-stink-bug

Soybean Pests Update

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth, Dr. Holly Schwarting and J.R. Ewing

Green cloverworms have moved into the pupal stage, for the most part, and thus have finished feeding on leaves.  There will probably be another generation of green cloverworms so any late planted soybeans may be at risk for defoliation again although it probably not enough to warrant an insecticide application.  Adult bean leaf beetles and stink bugs may also still be present in soybean fields and feeding on beans as long as they are still filling inside the pods, so monitoring should continue until pods are mature.

Sorghum Headworms and Soybean Podworms

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth, Dr. Holly Schwarting and J.R. Ewing

 

Most sorghum is at least flowering with much into milk, soft dough and even black layer.  Thus, headworm susceptible stages are mostly past as flowering to soft dough is the time frame for headworm vulnerability.  Once these advanced stages have been reached the head moth will start ovipositing in soybeans.  Soybeans then need to be continuously monitored, as long as there are new pods, for podworm damage and/or smaller podworms.

Soybean Pest Update

Posted on by Sharon Schroll

— by Dr. Jeff Whitworth, Dr. Holly Schwarting and J.R. Ewing

Green cloverworms have been causing considerable concern throughout the eastern 2/3rd’s of Kansas.  This has resulted in many acres treated to limit defoliation caused by these fragile little green and white striped worms.  Fungal-infected green cloverworms are also relatively common.  This fungus usually helps regulate green cloverworm populations, but remember, there is a lag time before the fungal infection decimates the larval populations, unlike an insecticide which usually works very quickly.

GCW fung

GCW defol

 

There are also a few yellowstriped armyworms still causing defoliation.  However, one yellowstriped armyworm larva collected in south east Kansas, brought into the lab appearing healthy, succumbed to a pathogen, probably a virus, within 3 days.  So, there are other factors working to help control many pest populations, i.e. fungal and viral pathogens.

YSAW viral