Taking an environmentally sensitive approach to pest management


Integrated Pest & Crop Management


Wayne C. Bailey
University of Missouri
Plant Science & Technology
(573) 882-2838

Webworm Problems In Double-Crop Soybean

Wayne C. Bailey
University of Missouri
(573) 882-2838

Published: August 4, 2009

During the past two weeks, many fields of double-crop and late planted soybean have experienced problems with webworms. These fields have covered a relatively large area including western and southwest Missouri. It is unknown which webworm species reached the economic threshold in these fields, although several webworms do attack soybean plants. Webworms eggs are laid on seedling soybean plants by small moths. These eggs quickly hatch with larvae moving to plant terminals to wrap plant tissues in pockets of webbing in which the developing larvae feed on foliage. The economic threshold for webworms in soybean is to treat when 10 to 12% or more of plants have heavy webbing on plant terminals and defoliation has reached 30% prebloom and 20% from bloom to pod fill. Webworms rapidly move through their life cycle with numerous small dull colored moths often seen in fields following completion of larval development. These moths generally move to other fields or hosts to lay eggs for the next generation.

Table 1. Webworms
Comments: Treat when 10% to 12% of plants show heavy webbing on top leaflets or when defoliation reaches 30% before bloom or 20% from bloom to pod fill.
Common Name Trade Name Rate of Formulated Material per acre Placement
permethrin *Ambush 25W 6.4 to 12.8 fl. oz. On foliage
cyfluthrin *Baythroid XL 1.6 to 2.8 fl. oz. On foliage
bifenthrin *Brigade 2 EC 2.1 to 6.4 fl. oz. On foliage
chlorpyrifos + gamma-cyhalothrin *Cobalt 13 to 26 fl. oz. On foliage
zeta-cypermethrin + *Hero 4.0 to 10.3 fl. oz. On foliage
zeta-cypermethrin *Mustang Max 2.8 to 4.0 fl. oz. On foliage
permethrin *Pounce 3.2EC 4.0 to 8.0 fl. oz. On foliage
gamma-cyhalothrin *Proaxis 3.2 to 3.84 fl. oz. On foliage
carbaryl Sevin XLR Plus 2 to 3 pt. On foliage
lambda-cyhalothrin *Warrior 3.2 to 3.84 fl. oz. On foliage
*Designates a restricted-use pesticide. Use is restricted to certified applicators only. Regardless of the formulation selected, read the label to determine appropriated insecticide rates, directions, precautions, and restrictions.

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REVISED: February 29, 2012