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Extension Entomology

Tag: green cloverworms

Soybean Update – Thistle caterpillars, Stink bugs, and Soybean Aphids

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Thistle caterpillars have mostly vacated their webbed cells and are or have pupated.  That is why there are huge numbers of painted lady butterflies flying around on most rural roads throughout north central Kansas.  Hopefully, these butterflies will head south for overwintering and will not start laying eggs in soybean or sunflower fields.  However, fields need to continue to be monitored for small thistle caterpillars, especially double-cropped soybeans. Additionally, monitor for the continued presence of green cloverworms, although these populations seem to be declining quite rapidly around north central Kansas.

 

Phytophagous stink bugs, both brown and green, are increasing in many soybean fields.  Either may insert their mouthparts into the seed within the pods and suck out juice from the developing seed.  However, there are also brown stink bugs that are predatory on pests like the yellowstriped armyworm (shown below) which has been killed and is being utilized as a food source by this beneficial stink bug.

 

Soybean aphid populations are still present in all fields examined this week in north central Kansas, but are not increasing in density or coverage.

 

 

For management decisions for all soybean pests please see the 2017 Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

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 Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Thistle caterpillars have not all pupated or emerged as adults yet in north central Kansas.  However, probably the majority of the larvae have finished leaf feeding and the adults have initiated oviposition.  There are still large numbers of adult butterflies navigating throughout soybean and sunflower fields.  Thus, scouting for the larvae should be an ongoing endeavor for probably another three weeks.

 

At the same time there are starting to be pretty good populations of green cloverworms in these same soybean fields.  Fields in the early to mid-reproductive stages are less tolerant to defoliation.  Populations last year caused considerable skeletonizing and resulted in many acres being treated.  However, there were also numerous fields that had green cloverworms controlled by an entomophagous fungus.

 

 

 

 

This highly visible white fungus will probably attack the green cloverworms again this year and may even do so, so effectively that insecticide applications are not necessary.  However, please keep in mind there is a lag time between a green cloverworm infestation of soybeans and larval infection by the fungus leading to their destruction.  But, they usually slow down or stop feeding soon after becoming infected, even if not actually killed for a few days.

Soybean stem borers seem to be relatively numerous around north central Kansas as well.  Oviposition by the females in the stem, at the site of the petiole attachment, is continuing.  Many eggs have already hatched and larvae are tunneling downward in stems where they will internally girdle around the interior of the stem and end up in the base of the taproot where they overwinter.

 

 

 

 

Spider mites are still present in north central Kansas, but so far seem to be very spotty.  These populations need to continue to be monitored during the plant’s reproductive stages.

 

 

Corn earworm larvae (soybean podworms) seem to just be getting started in south east Kansas and can cause considerable damage quickly by feeding on seeds within the pods.

 

 

Soybean aphids were first reported on 11 Aug, 2017, from the KSU Research Farm at Ashland Bottoms, just south of Manhattan, KS, by Rene Hessel and Bill Schaupaugh. These aphids have been found in the state every year since their first detection in 2002.  Beneficial’s are usually very active around these aphid colonies and help keep them from flourishing.  However, these small aphids need to be monitored periodically, especially in soybean fields treated for other pests, as these treatments may reduce the beneficial’s, and thus, any control which they may have provided.

For management of all these soybean pests, and others, please refer to the KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

 

Soybean Pest Update

— 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 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 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

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