No. 12 Article 5/June 11, 2004

Reports of Armyworm Injury Continue

Widespread reports of armyworms continued this week. Reports are no longer limited to the southern half of Illinois. Jim Morrison, Extension educator, crop systems, Rockford, also reported armyworm infestations of 4 to 6 larvae per square foot of row in wheat in Whiteside County. Larvae varied in size and were causing little damage to wheat heads. Several calls from Ford, Iroquois, and Kankakee counties indicated that several wheat fields were at or nearing economic thresholds and would be treated in the coming days. If you are treating wheat or other small grains for armyworms, please take pre-harvest intervals into consideration (Table 1).

Producers are reminded to scout wheat, corn, rye, and grass pastures for armyworms. Armyworms feed primarily at night, and injury often goes unnoticed until they have caused significant damage. Economic thresholds for armyworm in wheat are 6 or more non-parasitized larvae (3/4 to 1-1/4 inches long) per linear foot of row in wheat. Don't forget your cornfields; control may be justified in seedling corn when 25% or more of the plants are being damaged. Remember, armyworm populations may decrease due to parasitoids and diseases. Concurrent scouting trips spanning a few days will help determine if armyworm populations are increasing or decreasing. For more information on the armyworm, including rescue treatment options, please refer to issue no. 10 of the Bulletin (May 28, 2004). --Kelly Cook

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