Pest Alert

LAWRENCE, Kan. (DTN) -- Entomologists in Indiana, Illinois and Missouri are urging grass, wheat and corn growers to keep an eye out for true armyworms near or in their fields.

Southern Missouri growers are seeing high populations in fescue fields, University of Missouri Extension Entomologist Wayne Bailey told DTN. The state was due for an infestation, he added. "Armyworms have about a four- to five-year cycle, and the last time we saw them in Missouri in really heavy numbers was 2010," he explained.

Armyworms have been spotted in wheat fields in southern Illinois and, in Indiana, entomologists noted that corn fields that followed grass crops such as rye are also at high risk for an infestation.

A PERFECT STORM

A number of factors have combined to encourage armyworm infestations this year, Bailey said.

The moths caught early spring storm systems and winds and moved north from southern states where they had overwintered. In the more northern states like Missouri, armyworm larvae encountered fewer natural predators, such as parasitic wasps, possibly because of the unusually cold winter, Bailey added.

Finally, the wet, cool spring encouraged lush growth in fescue and wheat fields, providing the larvae with prime feeding grounds.

The armyworm prefers grass crops like fescue, but corn growers must be vigilant, too. Corn is a good candidate for armyworm feeding if it was planted behind wheat, grasses, hay or grassy cover crops that have been burned down. "Hatched larvae will move from the dying grasses to emerging/emerged corn," Purdue entomologist Christian Krupke and Integrated Pest Management Specialist John Obermeyer explained in the university's Pest & Crop publication.

Bt-traits or seed treatment will not necessarily protect corn from armyworm, Krupke and Obermeyer added. "Don't be complacent with Bt corn hybrids, as high armyworm infestations will still cause significant damage before the insecticidal proteins in Bt corn reduce their feeding," they wrote. "Seed-applied insecticides, even high rates, will NOT control armyworm."

Frequent scouting is the best way to ensure that armyworms don't strip your corn, wheat or fescue fields, Bailey noted. The worms are mainly interested in eating leaves, but they have been known to feed on kernels and wheat heads.

Once the worms get going, they can act quickly. "A lot of times in a wheat field, they'll cut 2% to 3% of the heads the first night, they'll cut about 50% the second night, and finish it up on the third night," Bailey said.

Because the worms start at the bottom of a plant when they are young, casual windshield surveys won't suffice. "People go driving by in their pickup and their field looks great, day after day, and then one day they drive by and there's no foliage left, because (the armyworms) have worked from the bottom up and eaten the whole plant," Bailey said.

Scouting procedures vary by crop. Corn growers should examine 20 plants in five different locations within a field, according to a publication from the University of Illinois' Department of Crop Sciences. When the armyworms are young and small, they avoid light, so be sure to poke around the base of the plant and peer into the corn plant's whorls.

Wheat growers should scan three feet worth of wheat plants in five or more areas within the field, the Illinois publication added. Scouts should note the size of the armyworms and the percentage of plants damaged.

Damage potential rises as armyworms get bigger in size. "Remember, once armyworm larvae reach an inch or more in length, they eat a tremendous amount of foliage in a short period of time and become harder to kill," Krupke and Obermeyer wrote. "Large areas of seedling corn can be wiped out overnight under heavy infestations."

Treatment thresholds vary by crop and location, and wheat growers should check post-harvest intervals of their insecticide before spraying. Check with your local Extension office for local thresholds, and use this University of Missouri publication which recommends thresholds and insecticides for corn, fescue and wheat: http://goo.gl/…

For help with identifying armyworm larvae and adults, see the University of Illinois Department of Crop Sciences' publication: http://goo.gl/…

Emily Unglesbee can be reached at emily.unglesbee@dtn.com

Follow Emily Unglesbee on Twitter @Emily_Unglesbee

(PS/CZ)

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