Physical Management of Swede Midge

Clean Transplants
Always start off with clean transplant material. This will not only help your operation but will reduce the movement of swede midge to other areas. Be confident about the source of your transplants.

If transplants come from an infested area or are possibly infested by swede midge, insecticide treatments should be applied before transplanting. Check what insecticides are labeled in your area. The effectiveness of different foliar sprays for control of swede midge-infested plants will vary depending on the time when plants became infested with swede midge. For example, in trials conducted at Cornell, the efficacy of acetamiprid (Assail) on swede midge using foliar sprays was 99.5, 100, and 99.8% when cauliflower seedlings were sprayed before inoculation with swede midge, at inoculation and 4 days after inoculation, respectively. The efficacy of acetamiprid was reduced to 69.9% when seedlings were sprayed 8 days after inoculation, and swede midge larvae could successfully pupate and emerge after the spray. Based on these results, foliar sprays on transplants at the early stage of infestation and before shipment of seedlings from swede midge-infested areas are recommended in New York. In the United States, Assail 30SG is not labeled for greenhouse use, thus plants must be removed from the greenhouse prior to treatment.

Refer to the label for specific product information. Inspect all transplants prior to planting, particularly in known areas of SM infestation. When hardening off young seedlings outside, cover them with fine netting or a floating row cover to prevent any egg-laying activity.

Post-Harvest Crop Destruction
The second most important thing that you can do to manage swede midge is to destroy your cruciferous crop as soon as possible after harvest. After the marketable portions (i.e. broccoli crown, cabbage head) are harvested, the plants sprout several secondary side shoots, which are ideal sites for swede midge to lay their eggs. Optimum host conditions in combination with the absence of insecticide sprays make post-harvest cruciferous plantings ideal for swede midge to thrive and build up very large populations – the larvae of which will drop to the soil to pupate, and then emerge in droves to find the next susceptible crucifer planting within the same season or the following spring. Leaving harvested cruciferous crops in the field post harvest is especially favorable for swede midge when the weather is still warm in July, August and September. In late October, November and December, swede midge activity drops considerably. Once you are finished harvesting a planting, it should immediately be chopped, disked or plowed, so that it no longer provides living tissue for swede midge to prosper. In western New York, pheromone trap catches tend to drop drastically after crop destruction. On the other hand, trap catches tend to steadily increase when a crucifer planting is left unattended after harvest.