Scout for Diamondback Moth in Canola | Northern Canola Growers Association

Several field reports of diamondback moth (adult) and young larvae were observed in canola fields from Fargo, Minot, Grand Forks and Crosby (Divide County) last week. This is the typical time when moths migrate into North Dakota.

The adult diamondback moth is a small gray moth about ½ inch long. Male moths have three diamond-shaped markings on the back of the forewing when the wings are folded together, hence the name diamondback moth. The newly hatched larva is light green and turns darker as it matures. Both ends of the larva are tapered, and the posterior end is forked. When the larvae are fully grown, they are about ½ inch long. When disturbed, larvae thrash backward violently and often drop from the plant, suspended on a strand of silk.

Start scouting regularly to see if larvae are present and populations are near economic thresholds. Diamondback moth larvae can be monitored in the field by pulling all plants from a 1-square-foot area. Beat collected plants onto a clean surface or into a white bucket, then count the number of larvae dislodged from the plants. Larvae often will dangle from canola plants on a silk thread. Repeat this procedure in at least five locations in the field to obtain an average number of larvae per square foot.

Canola is most susceptible to larval feeding from the second generation (July) injury during the flowering and pod stages. However, I have seen severe feeding injury to young canola in the seedling to 4-6 leaf stage (although not as common). You can also monitor for the adult moths using a commercial pheromone trap and lure from pheromone supply companies. Field scouting for larvae is encouraged if you capture more than 100 moths per trap per week. We are running a canola insect trapping network with our IPM Crop Survey Program. We are just getting started with canola insect trapping, but the trapping results will be posted weekly on the IPM website

(https://www.ndsu.edu/agriculture/ag-hub/ag-topics/crop-production/diseases-insects-and-weeds/integrated-pest management). Weather can dramatically impact larval populations, drowning them out during storms and increasing the risk of fungal diseases. Biological control, such as parasitoids, can negatively impact diamondback moth survival. If farmers need to treat Lepidoptera larvae (moths or butterflies) like diamondback moth, Vantacor is a newer mode of action, IRAC Group 22, Diamide. We tested it at the high labeled rate of 2.5 fl oz/acre, and it provided good to excellent control of the larval stage of diamondback moth. It also had a long residual of about 30 days. Diamondback moths can migrate into North Dakota with pyrethroid resistance from the southern states, so you don’t know if they will have pyrethroid resistance when they arrive. I have previously observed suspected pyrethroid resistance in DBM in northeastern North Dakota canola fields. For insecticides registered for diamondback moth management in North Dakota, please consult the 2025 North Dakota Field Crop Insect Management Guide E1143-25.

09 June 19 2025 CPR Final.pdf