Wheat Pest Problems to Watch for this Spring

Wheat Pest Problems to Watch for this Spring

April 13, 2007

Wheat prices and the recent moisture across most of the state has given wheat growers some optimism for the current wheat crop. In most years, insect problems in wheat are minimal, but problems can develop. It will be important to follow the wheat crop to prevent losses from pests during the remainder of the growing season.

Cutworms are the first insect pest consideration in wheat in the spring. Army cutworms can prevent green-up after dormancy. We have not received any phone calls about wheat green-up problems so this insect may not be a big issue this year in Nebraska. In Kansas some problems have been reported. In western Nebraska, especially in the southern Panhandle, the pale western cutworm may be present in significant numbers. Survival of this insect is enhanced during dry years, and we have seen significant moth numbers in pheromone trapping in the southern Panhandle. The eggs of this insect hatch in the spring (late March-early April) and the larvae feed from April to May. These cutworms are quite destructive as they feed below the ground cutting tillers off as they feed (Figure 1). Look for cut tillers laying on the soil between the rows and dig to find the larvae. The treatment threshold is set at 1-2 larvae per foot of row.

Hessian fly is another insect that can show up in the spring. A spring generation of Hessian fly can occur beginning in March or April. Damage will show up early as dark green plants, and later during the heading stages, as stems broken off near the base of the plant. Hessian fly problems result from early planting the previous fall allowing for a Hessian fly generation to occur on the wheat crop in the fall or by allowing volunteer wheat to grow from late summer through the spring and carry the fall generation of Hessian flies until the spring when the next generation will establish on the current wheat crop. Consequently there are no Hessian fly control options for infestations found in the spring.

Cereal aphids are another concern through the spring in wheat. Last year we observed greenbugs and other cereal aphids much earlier than normal because they were able to overwinter through the very mild winter. This year, due to the more "normal" winter weather, we likely won't see this; however, aphid problems can occur beginning in the late jointing to early boot stages. In western Nebraska, the Russian wheat aphid is the primary aphid threat. During regrowth to early jointing stages, look for leaf curling associated with purpling and yellow or white striping.

Threshold levels for the Russian wheat aphid range from about 5% to 25% infested tillers with lower threshold levels for wheat with high yield potential and higher thresholds for wheat with lower yield potential. The most critical time for control of the Russian wheat aphid is just before the flag leaf emerges. Treatments should eliminate aphids so the flag leaf emerges normally and the heads will not become trapped in the curled flag leaf.

Further information on scouting and thresholds for the Russian wheat aphid and other cereal aphids can be found at High Plains Integrated Pest Management Guide for Colorado, Western Nebraska, Wyoming, and Montana.

Gary Hein
Extension Entomologist
Panhandle REC, Scottsbluff

Online Master of Science in Agronomy

With a focus on industry applications and research, the online program is designed with maximum flexibility for today's working professionals.

A field of corn.