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Extension Entomology

Tag: grasshoppers

Alfalfa and Wheat “Worms”

–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

Wet weather has kept equipment out of the fields and has allowed the insects to flourish.  Fortunately, the plants are also doing well and tolerating these healthy populations of pests.  When these fields dry out and are able to be swathed, there will probably be relatively significant populations of alfalfa weevil larvae and adults still present.  They are accumulated into the windrows at cutting; they will feed on the stems under the windrows until the hay is picked up.  This causes the characteristic stripping in the fields where the regrowth under the windrows is chewed off while the areas beside the windrows grow back.  Once the hay is removed, the adult weevils will exit the fields and no longer be a problem.  Weevil larvae in north central Kansas on 7 May were 93% 3rd instar, and 7% 1st or 2nd instar.  There are many pupae and adults also.

weevil

weevil2

There are significant populations of aphids, mainly pea, in these central Kanas alfalfa fields as well.  Swathing will remove this problem, but there are many beneficial insects helping to regulate these aphids, and hopefully they will stay around after swathing to help manage any other aphids and/or potato leafhoppers that may show up (no leafhoppers detected yet).

aphidlacewing 2

Picture1lacewing

Some small grasshoppers were also noted.  Usually, grasshoppers do better in drier conditions, but not always.  So be aware that grasshoppers are present now and eggs will continue to hatch for the next month.

grasshoppergrasshopper2

—Dr. Jeff Whitworth and Dr. Holly Schwarting

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