Armyworms on the march

By JON GERSBACH Milam Agrilife Extension Agent

If you have pastures starting to grow since our recent rains, or will be planting small grains, a watchful eye should be turned toward the fall armyworm.

Fall armyworm larvae. (Photo courtesy of Department of Entomology, Texas A&M University, College Station.) Fall armyworm larvae. (Photo courtesy of Department of Entomology, Texas A&M University, College Station.) Producers should be especially vigilant when the weather turns cooler and frequency of rain increases, as it has recently. Late summer and early fall is the time of most concern to small grain stands, pastures, and hayfields. There have been some reports of armyworm infestation throughout the county and in neighboring counties.

The damage caused by armyworms can be devastating, especially if infestations are high at an early grow th stage in wheat and oat fields. Typically, a population of three to four armyworms per square foot will cause significant economic loss if not treated. However, early season infestations can experience losses at a population of less than two per square foot.

Armyworms are the immature larvae of small black to grey moths with white markings on the wings. These nocturnal moths lay their eggs in masses on the lower leaves and are covered with colored scales from the female moths' wings.

The lar vae, which do the damage to the crop, range in color from pale green to brown or black. Many times they are striped with white to yellowish lines from head to tail.

When scouting for armyworms, the best time to look is early morning or late evening, when they are most active. Look on the lower leaves, under clumps of soil, in cracks, fallen leaves, or clumps of dead grass. Often the worms will hide during the day in these areas.

The worms will not eat much when they are young, but as they mature, their appetite become ferocious and damages can occur very quickly. Eighty of the armyworms consumption is in the final days of the larval stage. Following this stage, they crawl into the soil to pupate and emerge 7-10 days later as a moth. The cycle will then repeat.

Two to three generations can occur during a growing season. For this reason, early detection and removal are very important The rapid destruction of pastures is how the armyworm gets its name, because the damage is quick and will move across the field much like an army marching across in search of more foliage to feed on.

The armyworm has natural predators including birds and other insects, but if the population is too high, there are not enough to predate the armyworms. This disrupts the natural balance and damage can occur.

For control recommendations, contact our office for a factsheet and options, as there are many different products available with different grazing restrictions.

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2009-09-24 digital edition

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