By: Scott Hartley, PAg, Provincial Specialist, Insect/Vertebrate Pest Management
While scouting fields early this season it is important to distinguish poor crop establishment from insect damage and other problems. Two potential insect pests are wireworms and cutworms, but there are often other insects present that are inconsequential or beneficial to the crop.
Wireworms are the immature forms or larvae of “click” beetles. Wireworms and most of their damage tend to be more abundant in moist soils and in lower, damper areas of a field. Although wireworms often prefer grassy plants (cereal crops), wireworm damage has been noted in and can be significant in other crops including canola, chickpea, lentil and potato. Wireworms tend to shred the plant tissue below the soil surface. Initially, symptoms may appear similar to drought, with wilting in the main central leaves but can eventually cause death to the plant. Controlling wireworms requires the use of an insecticidal seed treatment and damage may not be noticed early enough in the season to reseed. There are no foliar insecticides registered for control of wireworms.
Unlike wireworms, cutworm damage often results in the plants being severed at or near the soil surface. However, some cutworm species feed on foliage growing above ground. The pale western and red-backed cutworms are two species commonly found in Saskatchewan soils, and both feed off the seedlings at or below the soil surface. Other cutworm species that occur in the province include dingy cutworms, usually in eastern regions, and army cutworms, which have been reported in western regions. Dingy and army cutworms feed above ground, consuming the plant foliage. Typically, but not always, cutworms are more likely to cause damage on hilltops, south-facing slopes and in drier areas of a field. If damage to seedlings is a result of cutworm feeding, a foliar application of an insecticide may be an option. Depending on the crop, there are chemical control options for cutworms. Refer to the 2017 Guide to Crop Protection for registered insecticides for insects in specific crops. For more detail on cutworm species, see the new booklet released by Agriculture and Agri-Food Canada.
Some of the other organisms present in soil include Enchytraeds, which are small (less than 20 mm), translucent and “earthworm-like” when viewed under magnification. Similar to earthworms, these move slowly and are beneficial in assisting in breakdown of detritus in the soil. Stiletto (Family Therevidae) fly larvae are also pale white, slender and small, but react with rapid whip-like motions when disturbed. Stiletto fly larvae are unique in the fly families in having a hardened head capsule. The head area is often indistinguishable in fly larvae. This species is beneficial as a predator on other insects, including wireworms. Crane fly (Family Tipulidae) larvae do not have the hardened head area, but have extensions on the hind end. Crane fly larvae, also called leather jackets, can be a pest in turf grass, but have not been shown to be economic in cereal crops. Scarab beetle larvae have sometimes been found in fields and occasionally have caused some damage to canola crops but actual economic damage has not been confirmed.