True Armyworm Alert

True Armyworm infestations have been reported this week in eastern and western NY, as mentioned in the View from the Field. GET OUT AND LOOK NOW!

It is important to detect armyworm areas early, while larvae are still small, since large larvae do most of the feeding and quickly destroy whole stands of corn, grasses and small grains. Because armyworm feeds at night look for chewed leaves, cut stems, lodged plants, pellet-like frass on the ground, and larvae hidden under plant canopy and surface residue. You will need to be aware that armyworms can move from field to field every quickly. If there are sufficient numbers and damage is present, an insecticide could be justified. Larger armyworm larvae, greater than 1 inch long, are much more difficult to control. These large larvae are more tolerant of insecticides, reducing the effectiveness and economic viability of this option. REMEMBER… if you have an infestation in a mixed stand true armyworm, alfalfa and the grass ALL NEED to be on the LABEL!!!

True armyworm larvae appear smooth cylindrical pale green too brownish when they are still small. Mature larvae are smooth and marked with two orange, white-bordered strips on each side. True armyworm ranges in size from 1/8 inch to 1 .5 inches long.

Economic Threshold Guidelines for True Armyworm 

Corn – For seedling stage corn Penn State recommends For whorl-stagecorn, apply an insecticide only if most plants show damage and about three larvae per plant are found.

Wheat – 3 to 5 or more larvae square foot, larvae less than 1.25 inches and not parasitized, watch for flag leaf reduction or if grain heads clipped off – yield losses, a spray before soft dough to save the remaining 3 upper leaves is generally beneficial since these tissues are still important to grain filling.

Grasses – no specific guidelines available, need for treatment based on the level of damage observed in relation to the expected value of grass harvest.

Identification Resources:

Armyworm as a pest of Field Corn: Armyworm on Wheat: Common (True) Armyworm: Fall Armyworm:

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