When we hear the term “worm”, we often think of beneficial earthworms and their kin. Unfortunately, the term “worm” can also be used to describe several pest species in wheat such as wireworms, cutworms, and armyworms. Wireworms are the immature stage of the click beetle. They can be a ¼- to ¾-inch long and have slender, semi-cylindrical bodies. They can be white, yellowish, or coppery in color and have three pairs of legs behind the head. Cutworms and armyworms are not worms either, they are caterpillars. Cutworms and armyworms can be distinguished by their color, striped pattern, having a distinct head capsule and three pairs of legs including abdominal pro-legs with hooks called “crochets” that aid in climbing (Figure 1).
Common species in our region are the variegated cutworm (Peridroma saucia), western yellowstriped armyworm (Spodoptera praefica), army cutworm (Euxoa auxillaris), and Bertha armyworm (Mamestra configurata) to name a few.
Recently, in Waterville and surrounding areas, there has been talk of finding “worms” in low-lying spots of winter wheat fields and wanting to know what type of insecticide should be used to prevent damage. The “worms” in question that have been brought in for identification are the larval stage or maggots of the European crane fly (Tipula paludosa) or prairie crane fly (Tipula simplex). The larvae are tan to grey without stripes, have no head capsule and lack any type of legs (Fig 2). The outer skin in mature larvae becomes hardened over time and they take on the name “leatherjackets.”
They feed on the roots of many different grasses and crops, including wheat, especially following CRP take-out. Spring wheat at the seedling stage is most vulnerable and vulnerability lessens as the wheat matures and tillers. The treatment or action threshold is 50 maggots/m². I have not seen infestations close to this threshold. If crane fly larva numbers are still high after CRP take out, a seed treatment containing imidacloprid such as Attendant 600 FS or others should be considered before planting. If pest numbers exceed thresholds within the crop, then foliar-applied products containing the active ingredient chlorpyrifos such as Warhawk, or the active ingredient lamda-cyhalothrin, which can be found in Grizzly Too, LamCap II Insecticide, or other products can be used. Be sure to read and follow the pesticide label instructions before use.
For questions or comments, contact Dale Whaley via email at dwhaley@wsu.edu or phone at 509-745-8531.