By: Scott Hartley, PAg, Provincial Specialist, Insect/Vertebrate Pest Management
Cutworms continue to be a concern for producers this spring. Infestations have been reported in lentil, canola, wheat and barley in most regions of the province. Climatic conditions, primarily temperature, may have accelerated development of the larvae this spring.
Species such as the army (Euxoa auxiliaris) and dingy (Feltia jaculifera) cutworms hatch from eggs laid the previous fall and overwinter as partially grown larvae. These cutworms pupate near the middle of June. Other species such as red-backed (Euxoa ochrogaster) or pale western (Agrotis orthogonia) cutworms that hatch from an overwintering egg in the spring usually complete their larvae stage and pupate near the end of June. However with the higher temperatures, pupation may be earlier in 2016.
Cutworms are nocturnal, generally staying below ground during sunny days and coming to the surface to feed in the evening or at night.
Foliar insecticides are registered for control of cutworms. Refer to the 2016 Guide to Crop Protection for registered products in specific crops. Economic thresholds depend on the cost of control and the value of the crop and can therefore vary from the recommended level. For example, if the value of the crop increases or the cost of control decreases, the economic threshold could be lowered.
Insecticides should be applied by spray to the soil surface in the evening to avoid daytime pollinators and high temperatures. For some insecticides, efficacy is reduced when temperatures exceed 25 C. Cutworms come in contact with the chemical when they come to the soil surface to feed. Higher water volumes can be beneficial for better coverage and soil penetration. Keep in mind that it can take up to 10 days for optimum control since not all larvae come to the surface on any given night.
Other factors that can affect control include the level of infestation, size of the larvae and crop stage. Higher populations and larger cutworms will be more difficult to control and will require higher rates. A lush crop canopy will prevent the chemical from reaching the soil surface and intended target, resulting in untreated spots and reduced efficacy.
Once the cutworms start to pupate, feeding will stop, making control efforts unnecessary. Since cutworm moths lay most eggs in August and early September of the preceding year, maintaining weed free fields later in the summer is advantageous as they are not a preferred location for females to lay eggs.