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Soybean Pest Update

— 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

 

Soybean Pests Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Green cloverworm larvae have been rapidly increasing all throughout the eastern 2/3rds of Kansas.  These worms are very well camouflaged and usually feed on the underside of leaves, thus are not always evident until holes start showing up in leaves.

green cloverwomr larva

soybean defoliation

There has been concern relative to this leaf feeding but generally it is not until the density reaches 10-12 larvae/ row ft. with about 30% defoliation, and larvae are still small (1/2 inch or less) that an insecticide application may be justified.  However, in past years when those cloverworm densities have been achieved there has been an entomopathogenic fungus that rapidly decimates the populations.  This seems to be starting this year, as the first fungal-infected green cloverworm larvae were noticed on 23 August in several counties in Kansas.  This fungus causes the green cloverworm larvae to stop feeding after 12-24 hours of infection and causes death 24-48 hours later.  Sometimes, these infected larvae still look alive even in death, which is one of the characteristics of this fungus.  There will probably be at least one more generation of green cloverworms to come.

fungal GCWfungal GCWs

Don’t forget to continue monitoring for adult bean leaf beetles, stink bugs, and podworms, all of which may feed on pods and/or seeds.  There will probably be one more generation of podworms this year.  For more information on soybean pests please see Soybean Insect Management 2016, available here: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

Soybean Pest Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

What a difference a few days makes in the world of insects!  Two weeks ago, and prior, there were very few insect pests in soybeans throughout north central and south central Kansas.  Now, most soybean fields are loaded, with more coming all the time.  Some of the insects common to soybean fields throughout north central, south central, and south east Kansas right now are as follows:

Dectes stem borer adults. These have been actively depositing eggs in petioles for a few weeks although populations seem somewhat reduced compared to the past few years.  Larval tunneling within the petiole and resultant petiole death has not yet become very apparent.

Dectes

Bean leaf beetle adults. These feed on the leaves, usually causing mostly round or oblong holes, which are of little consequence.  However, these same adults can also feed on the pods which may damage the bean inside and thus cause significant yield reductions.

bean leaf beetle feeding

Bean leaf beetle

bean leaf beetle pod feeding

“Worms”. There are also significant numbers of a variety of “worms” or caterpillars in most soybean fields.  These include various stages of yellowstriped armyworms, which may feed on the leaves but not enough to impact plant health or yield.

yellowstriped armyworm

There are also numerous green cloverworms, which are also leaf feeders.  These are the “inchworms” that wiggle like crazy when disturbed.

green cloverworm_feeding

They are usually highly susceptible to a fungus that turn infected larvae white and decimates the population rapidly over large areas.  Green cloverworms may cause a great deal of concern because of the defoliation they cause, but rarely are they any real detriment to the plant.  However, make sure to properly identify the worms as there are also corn earworms, aka soybean podworms, which may be mistaken for green cloverworms.

Soybean podworm

Soybean podworms will feed on leaves but more worrisome is when they start feeding on the developing seeds within the pods.  Two or three pods fed on per plant may justify control if there are still larvae in the field.  Otherwise, they may have pupated and treatment should be delayed until sampling indicates the next generation of larvae is actively feeding on seeds within pods.

Alfalfa caterpillars are also feeding on leaves and adding to the worm variety but will not cause any detrimental impact on yield.

alfalfa caterpillar and green cloverworm

Chinch Bugs

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Chinch bug populations continue to cause concern in north central and south central Kansas.  Occasionally, in past years when rainfall was plentiful and humidity high, chinch bugs were controlled by an entomophagous fungus.  However, this always occurred during the ‘walking migration’, when the nymphs were aggregating in wheat and started moving out as the wheat senesced, to feed on nearby seedling sorghum and/or corn if adjacent to wheat.  The chinch bugs are now more dispersed around sorghum fields and therefore the fungus may infect a few bugs but will probably not help control these populations which are increasing and therefore need to be monitored.  For more information on chinch bug biology in Kansas, please visit: http://www.bookstore.ksre.ksu.edu/pubs/MF3107.pdf

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