April 20, 2007

Table I. Threshold and treatment considerations for army and pale western cutworms.
	Threshold (worms per square foot)	Factors to consider in treatment decisions
Army cutworm		1. Is damage primarily from leaf feeding? 2. How many cutworms per square foot? 3. What is the stress level of the crop? 4. Will it recover if cutworms are controlled? 5. Is the plant growth rate greater than the defoliation rate? 6. What is the yield potential (value) of the crop? 7. What is the cost of control? 8. What size are larvae? Will they pupate soon? 9. Does the infestation cover the entire field? 10. Will a treatment of only the infested area of the field be practical? cost effective? 11. What will temperature and moisture conditions be like after treatment? Will insecticide be effective at low temperatures?
alfalfa - new stand	2 or more
alfalfa - established	4 or more
wheat - thin stand	2 or more
wheat - good stand	4 or more
Pale western cutworm		1. Are tillers wilting or dead? Are tillers cut off and easily pulled up? 2. Is the infestation confined to hilltops? 3. Are infestations spreading to other areas? 4. Are cutworms surviving well? (see numbers 2-11 above)
wheat	1-2 per ft. of row

It is difficult to predict what the last few weeks of below normal temperatures will do to the insect populations across the state. At the very least, insects that had become active before the extreme cold of two weeks ago were stressed by the conditions. Insects that had not come out of their winter dormancy were likely not affected. Development according to growing degree day models for alfalfa weevils came to an abrupt halt and accumulations are just starting again. Without knowing for sure what the effects were, alfalfa fields need to be scouted to make sure the insects don't "sneak up" on us while we rush to plant our spring crops.

Alfalfa and wheat can be affected in the early season by several insect pests. In wheat, army cutworms and pale western cutworms can cause problems. In alfalfa, army cutworms and alfalfa weevils can cause severe damage.

Army Cutworm and Pale Western Cutworm in Wheat

Wheat can be scouted for damage as soon as it is green and growing. Most activity from these insects occurs in the western third of the state but army cutworms can be found over the entire state. The army cutworm overwinters as a partially grown larvae and the pale western cutworm overwinters in the egg stage; however, pale western cutworm eggs hatch in February and March during warm spells, so both of these cutworms should be in the larva stage at this time.

Army cutworm larvae will be dark and slightly larger than pale western cutworm larvae, which are a light color (see Figure 1). Look for both of these cutworms in the soil near the base of the plant during the day, since most of their above ground activity occurs at night. The army cutworm tends to feed on the leaves and may be less serious, but the pale western cutworm tends to feed lower, below the growing point, and may thin stands by killing plants. Injury symptoms may resemble freeze damage so if wheat damaged by the cold temperatures isn't recovering like it should, these insects may be the problem.

Treatment thresholds are two to four per foot of row in wheat for army cutworm and one to two per foot of row for pale western cutworm, depending on stress and moisture conditions.

Baythroid (cyfluthrin), Mustang Max (zeta-cypermethrin), Warrior (lambda cyhalothrin), Proaxis (gamma cyhalothrin), Lorsban (chlorpyrifos), methyl parathion, endosulfan and many generic products are available for control.

Army Cutworm in Alfalfa

Army cutworms also may prevent green-up of alfalfa by feeding on the new growth. Entire fields can remain brown for a week or more after normal green-up usually occurs. Often patches of a field will green up later than others. Again, these larvae are nocturnal and will be hiding in the soil around the crowns of the alfalfa during the day. The threshold for army cutworms in alfalfa is two or more per square foot on seedling alfalfa and four or more per square foot for established stands.

Keith Jarvi
Extension Entomologist
Northeast REC, Norfolk