Check soybean fields for webworms

Webworms are being spotted in SW Kansas in double cropped and late planted soybeans. In Kansas, these moths can have multiple generations per year, with the bulk of the damage to soybeans occurring in July and August. Scout these soybeans fields often as these caterpillars can defoliate a young soybean crop in just a few days. There are two species, the garden webworm and the alfalfa webworm, that will attack soybeans.  Pigweeds are one of the preferred foods of the garden webworm. When these weeds are sprayed with herbicide, the larvae move in mass to their secondary host, soybeans. The alfalfa webworms will migrate from alfalfa after it has been harvested. High numbers of these moths have been seen flying in alfalfa fields recently, but harvesting the alfalfa will eliminate eggs the moths may have laid.
Image Garden webworm on pigweed.

ImageEarly instar webworm on soybean seedling.


The garden webworm, Achyra rantalis. Webworms will line their feeding site with silk, often tying one or more leaves together.

ImageWebworm feeding damage in soybeans can be recognized by leaves having a window pane look with frass pellets mixed within the silk.


ImageThe garden webworm can be easily distinguished from the green cloverworm by its appearance and damage.

The webworm has three spots in a triangle formation on each segment and 4 abdominal prolegs, while the green cloverworm has no spots and has three abdominal prolegs. The green cloverworm chews irregular holes in the leaves and will not clump leaves together with silk. Both of these larvae can act erratically when disturbed.

For control options in soybeans :

Green cloverworm: 

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