How do you prevent pests on leeks?
Written by
Olivia Mitchell
Reviewed by
Prof. Charles Hartman, Ph.D.Protecting cut leeks from pests the organic way. One of the most important and practical steps is to prevent onion maggots and leek moths from ruining what promises to be a crop of leeks to be proud of. Remove any old onion bulbs beforehand. Understand the pest's lifestyle - when they breed, where they lay eggs, and how long it takes for the first egg to hatch. With this knowledge, you can put effective barriers in place and prevent the little blighters from attaining adulthood and becoming your next problem.
Physical Barriers
- Install floating row covers during spring egg-laying periods
- Use fine mesh (0.6mm) to exclude onion maggot flies
- Secure edges completely with soil or boards
- Remove during flowering for pollination if saving seeds
Biological Controls
- Apply Bacillus thuringiensis (Bt) for caterpillar infestations
- Introduce beneficial nematodes against soil-dwelling larvae
- Encourage ladybugs and lacewings for aphid control
- Use spinosad sprays for thrips management
Cultural Practices
- Rotate alliums to new beds annually
- Remove plant debris where pests overwinter
- Interplant with pest-repelling companions like carrots
- Time plantings to avoid peak pest cycles
Row covers provide important physical protection during those crucial periods. Place them over the crops using the lightest-weight material you can find, which allows for 85% light transmission (the absence of light is deadly). Make sure to secure all edges completely; otherwise, you will have unwelcome insects. Leave these on through flowering if you are not planning on saving seed.
Neem oil applications: Disrupts the feeding and breeding cycles. Use 2 tablespoons per gallon of water, add a few drops of soap. Spray liberally, both sides of leaves thoroughly. Early morning or late evening is best to prevent burning leaves. Reapply after heavy rain washes off the coating.
Crop rotation foils the life-cycles of pests. Never plant alliums in the same bed for two consecutive seasons. Move your leeks at least another 300 feet away from last year's alliums. Do not plant another in their original beds for at least three years beyond that. This keeps pest populations from becoming established in the soil.
Companion planting camouflages the scent of leeks from predators. The idea is to grow carrots near leeks to repel leek moths! Placing celery between the rows can confuse onion flies. Strong-scented herbs such as rosemary and sage are also good companions that create a kind of cloaking tactic.
Regular monitoring catches problems early. Inspect your plants weekly for eggs, larvae, or damage. Check the underside of leaves where pests tend to hide. Keep a record of when pests first appear each season. If you detect them early, you can isolate the problem before it becomes severe.
Read the full article: 10 Essential Steps for Growing Leeks
