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Issue No. 8, Article 6/May 18, 2007

Armyworm Activity Deserves Attention

Ron Hines, FS seed agronomist for Growmark's southern region, and other crop specialists with FS found small armyworm larvae feeding on the flag leaves of freeze-damaged wheat in Randolph and Monroe counties on May 4. The larvae were relatively small (3/8 to 3/4 inch). In Madison County on May 8, they found as many as 12 larvae per foot of row, and some of the larvae were longer than 3/4 inch. The published threshold for armyworm control in wheat is six or more non-parasitized larvae (3/4 to 1-1/4 inch long) per linear foot of row before extensive head cutting occurs. Consequently, their findings of armyworms in Madison County wheat fields suggested that insecticide applications were warranted.

Many references have been made to the armyworm outbreak in 2001, with comparisons of these early observations of armyworms in 2007. It's quite likely that the environmental and ecological circumstances in 2007 will differ from those that prevailed in 2001. In fact, the one obvious major difference between the two years is that there will be less wheat to support populations of armyworms in 2007. This could result in starvation of some larvae, and it certainly will result in armyworm larvae's moving more readily in search of other food sources, including corn. So in 2007, possibly more than in previous years, growers should be especially watchful for signs of armyworm injury to corn leaves that start to show up along field edges.

We also need to remember how much damage armyworms caused to grass pastures in 2001. Many farmers were caught off-guard with the seemingly sudden appearance and intensity of armyworm injury in grass pastures that year. Although it is not always easy to find small armyworms in grass pastures, careful scrutiny now could pay big dividends very soon if lots of larvae are found. The use of a sweep net may help in your search for armyworms, but remember that armyworm larvae tend to be nocturnal and are usually curled up on the ground near the plant crowns or under debris during the day.

Insecticides suggested for control of armyworms in corn, wheat, and grass pastures are presented in Table 2. Please read and follow all label directions and precautions.--Kevin Steffey

Kevin Steffey

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