|How do I know if I have cutworms?
Early symptoms of damage include small holes or semicircle notches eaten in the foliage and seedlings severed just below the soil surface. Later on, cutworm larvae will sever plants at or just below the soil surface. You need to be checking the fields on a regular basis to catch the problem early. Without regular field checks what is often observed is a crop that has emerged well and then seems to deteriorate. If conditions are dry producers may feel that the crop is just suffering from the poor growing conditions. As the thin areas grow it becomes apparent that the problem is more than just weather and upon closer examination wilted and dead plants are found. If you look around the outside edge of where the damage has occurred and in the seed row close to recently severed plants you’re likely to find the cutworm just below the soil surface were the dry and moist soil meet. The larvae move here to escape the daytime heat.
How do I know if I should do something to control the cutworms?
Once you’ve identified that you have a problem the next step is to determine how serious the problem is. The economic thresholds for chemical control of cutworms vary from 1 to 4 larvae per 30 cm (12 inches) of row depending on the cutworm species, crop and crop stage. For more details on thresholds check out these links:
Economic Thresholds for Insects Attacking Cereals and Corn
Economic Thresholds for Insects Attacking Oilseeds
What do I do if the economic threshold is reached?
Once you’ve made the decision to control the cutworms you need to choose a product that is registered for both the crop and this pest. Matador, Decis, and Lorsban are examples of chemicals that can all be used to control cutworms. For more chemical choices consult your local agronomist, the 2004 Crop Protection Guide and/or our The Blue Book on the web site.
Chemical control should be done from late afternoon to evening. The reason for spraying late is that cutworms feed at night and to get control you need to apply the chemical as close to the time that they emerge as possible.
If you want to learn more check out the information at our website or contact us at: 310-FARM (3276)
Prepared by Ken MacDonald, Ag-Info Centre, Alberta Agriculture and Rural Development