Grass seed-Sawfly

Dolerus nitens
Pachynematus setator

Pest description and crop damage Adults are predominantly black with brownish legs and markings on the body. They are not "true" flies, but are related to wasps. The female's abdomen is distended greatly at emergence, and the intersegmental membrane is translucent greenish blue. Eggs are small and green at first, but after about a week they turn yellow, and the plant tissue around them turns dark reddish brown.

Larvae look like "many-legged" armyworms, except that the sawflies have abdominal prolegs on almost every segment of the abdomen. Armyworms, cutworms, and most caterpillars have prolegs only on abdominal segments 3, 4, 5, and 6.

Early instars are pale yellowish green but turn gradually to a vivid green (around 0.75 inch long at final instar). The pupae are green, gradually darkening with age. They are found at the soil surface around the periphery of plant crowns.

The larval stage feeds on leaves and chews through stems, resulting in the loss of the entire seed head; or, if the stem is not entirely severed, harvested seeds are usually sterile.

Biology and life history Adults emerge in April. Mating is within 1 or 2 days, and the females begin laying eggs on leaves. The eggs hatch in 7 to 10 days, and the larvae feed for 3 to 4 weeks while going through several instars. The larvae drop to the ground and spin cocoons on the soil in the duff. They remain in and on the soil until spring. There is one generation per year.

Management-chemical control

  • lambda-cyhalothrin (Warrior) at 0.02 to 0.03 lb ai/a. PHI 0 days for grazing and cut for forage, 7 days for straw and seed crop. REI 24 hr.
  • lambda-cyhalothrin/chlorantraniliprole (Besiege) at 6.0 to 10.0 fl oz/acre. PHI 0 days for grazing and cut for forage, 7 days for straw and seed crop. REI 24 hr. Do not exceed a total of 27.0 fl oz of Besiege or 0.09 lb ai of lambda-cyhalothrin or 0.2 lb ai of chlorantraniliprole per acre per year.

Field experience has shown that carbaryl or any of the pyrethroids as applied to control armyworm give good control.