Fall Armyworms Invade Ozark Region

Farmers report damage in alfalfa, ryegrass, even fescue fields.

Published on: Oct 5, 2010
University of Missouri Extensions specialists in southwest Missouri have received numerous reports about extensive damage on forages such as rye, ryegrass, wheat, alfalfa, brome grass and fescue, by armyworms.

"Many of these armyworms are very small and are doing lots of damage. They will likely be around until frost so more damage is likely," says Tim Schnakenberg, agronomy specialist with University of Missouri Extension.

The economic threshold for forages is four half-grown or larger larvae per square foot. Perennial plants (fescue and brome) can survive extensive damage, though production will be diminished this fall.

Alfalfa and clover can be damaged by the larvae, causing it to be less thrifty going into the winter and weakening the stand.  New stands are particularly at risk and must be sprayed. The economic threshold for alfalfa is to spray when you reach two or more half-grown or smaller larvae in the field. 

"I'm concerned that annuals like wheat, rye, triticale and ryegrass may have the greatest damage. Young seedlings that are consumed to the ground may not recover," Schnakenberg says.

Some products that will work on fall armyworm include Mustang Max, Warrior, Sevin, methyl parathion, Pounce and malathion. Sprays are only needed if damage is extensive and it compromises the stand and fall production.

MU Extension specialists have also seen extensive damage on ryegrass species in the last week with root rots. "Several farmers have had this problem. I'm not sure which root rot it is but it has affected many fields," Schnakenberg says.

Many times a good stand comes up then turns yellow, then red and dies. Close observation shows roots rotting away. If farmers replant, Schnakenberg notes they should use a seed treatment or treated seed since the inoculum is still in the soil.

"There is still time to plant cereal crops, though fall grazing potential will be less," Schnakenberg says.

Source: MU Extension Southwest News Service