Kansas State University

search

Extension Entomology

Tag: cloverworms

Soybean Update – Green Cloverworms, Thistle Caterpillars, Stink Bugs, Soybean Aphids, and Beneficials.

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Insect activity is still increasing around north central Kansas.  One positive, bean leaf beetles seem to be at really low densities in most fields, at least so far.  Green cloverworm larvae are at various developmental stages but there are still many early instars.  This means there probably is considerable defoliation to come because, as the larvae get larger, they simply eat more leaf tissue.  However, as green cloverworm populations increase, they are often infected with an entomophagous fungus which decimates their populations.

 

There also are many areas with significant infestations of thistle caterpillars and garden webworms.  Both species web leaf tissue around and over themselves, creating a relatively secure area from which they feed on leaves.  Many thistle caterpillars are really small right now and may not be noticed yet.  So, continued monitoring is important, especially with soybeans just entering the reproductive stages of development.

 

Green stink bugs are relatively common in both conventionally planted and double-cropped soybeans.  There are eggs, nymphs, adults, and mating adults all present at this time so sampling needs to be conducted periodically as these bugs can feed on the beans while they are developing inside the pods.

Soybean aphids were detected in double-cropped soybeans in Dickinson Co. on 24 August. Many soybean fields have significant populations of green lacewings and lady beetles, both of which may help control soybean aphids if and when they migrate into these fields.  So, as always, please take these into consideration if insecticide applications are contemplated.

 

For more information of thresholds and management options for these pests, please refer to the KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

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

 

Subscribe

Follow this blog

Get every new post delivered right to your inbox.