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Extension Entomology

Tag: defoliation

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

Posted on by Sharon Schroll

–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

Alfalfa and Wheat “Worms”

Posted on by Sharon Schroll

–by Dr Jeff Whitworth and Dr Holly Schwarting

Wheat and alfalfa fields throughout south central and north central Kansas should be monitored for signs of defoliation.  Many pests can defoliate either crop this time of year, i.e. grasshoppers and flea beetles (usually around borders), and “worms”.  These larvae are most commonly armyworms, fall armyworms, and/or army cutworms.  Identification is important for these “worms” because armyworms and fall armyworms will feed until the temperatures cool into the mid-20’s or they pupate, whichever comes first.

armyworm

fall-armyworm

 

Army cutworms, however, are and have been hatching from eggs deposited by moths as they return from over-summering, probably in Colorado.

army-cutworm

These army cutworm larvae will feed a little this fall, overwinter, then start feeding again in early spring.  So, if the “worms” causing the defoliation now are relatively large, ½ inch or more, they are probably armyworms and/or fall armyworms.

 

We have been hearing about and seeing a mixture of both armyworms and fall armyworms (see pics below).  These small worms start by causing small “windowpanes” in wheat or alfalfa.  No army cutworm infestations have been verified yet.

small-worm-1

small-worm-2

windowpane-feeding_wheat

Flocks of birds in wheat or alfalfa fields in fall or early spring are often indicative of a “worm” infestation as the birds are feeding on the larvae.  Fields with 25-30% of the plants showing “windowpane” feeding need to be monitored frequently as these larvae consume more as they get larger.  Treatment should be applied before stands become threatened.  For more information on treatment thresholds and management options please see the Wheat Insect Management Guide: http://www.bookstore.ksre.ksu.edu/pubs/mf745.pdf

Alfalfa Update

Posted on by Sharon Schroll

–Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevils are still active throughout north central Kansas.  Even fields that had insecticide treatments which were well timed and effective have been having more larval feeding.  These fields need to be treated again as soon as possible as these larvae are still capable of considerable defoliation for the next week or so, especially as we continue to see the fluctuating temperatures.  Remember, these are contact insecticides so coverage is very important.  Also, please pay attention to the pre-harvest interval (PHI) for whatever product you use as many fields are getting close to that first cutting.

AW larva 28 Apr

AW damage 28 Apr

Soybean Pest Update

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Double cropped soybeans are still very much in the reproductive stages throughout north central Kansas.  Thus, they are still vulnerable to a variety of pests – and pest populations seem to be increasing.  Green cloverworms (see pic) have been feeding on leaves for the past couple of weeks but are starting to cease feeding to begin pupating.  They rarely cause actual yield loss but usually cause concern because of the amount of defoliation they often cause.  While green cloverworms don’t feed on the pods or seeds, adult bean leaf beetles and corn earworm larvae (a.k.a. soybean podworms) do (see pics).  Both species, bean leaf beetles and corn earworms, seem to be increasing throughout south central and north central parts of the state.  The corn earworm larvae will usually feed on the seed within the pod and will only feed for about 10-14 days.  However, bean leaf beetles will continue to feed until harvest, or they disperse to overwintering sites.

green cloverworms

 

Adult BLB

BLB pod feeding

 

CEW pod feeding

 

There are still a few soybean aphid populations in north central Kansas, however there are more winged adults present which probably means they are mostly finished feeding and preparing to migrate to overwintering sites (they probably do not overwinter successfully in Kansas – we hope).

We have received several calls this week relative to these “interesting little green worms” in soybeans.  These are silver spotted skipper larvae and will feed on leaves but should not defoliate enough, on a field-wide basis, to impact yield.

silver spotted skipper

 

Alfalfa Pests

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa continues to cause concern throughout north central and south central Kansas due to defoliation by “worms”.  There seems to be a combination of garden (alfalfa) webworms, fall armyworms, armyworms, yellow striped armyworms, etc. feeding on the foliage.  Generally, if the alfalfa is within 10 days of swathing or if the “worms” are mature, (maybe ½ inch long for webworms which are naturally smaller than the others; or ¾ inch long for the others), it probably is best to just cut the field and not treat.  If treatment is justified, please pay attention to the pre harvest interval (PHI) for whatever product is used.  These worms won’t feed on the foliage after it is cut, but they may feed under the windrows holding back the regrowth and causing striping in these fields.  For more information on these insects and their control options, as well as PHI’s, please visit: http://www.bookstore.ksre.ksu.edu/pubs/MF809.PDF