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Extension Entomology

Tag: thistle caterpillars

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 Update

–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.