Garlic IPM Newsletter No. 6 — May 22, 2025
Leek Moth
Leek moth is a pest of allium crops that was first found in the US (New York) in 2009. It is not widespread in Maine – it was identified in Franklin and Somerset counties in 2021 but not since. However, because leek moth is problematic in other northern New England states and neighboring Canadian provinces, UMaine Cooperative Extension and the Maine Dept. of Agriculture, Conservation, and Forestry regularly monitor for its presence.
Leek moth primarily feeds on leaves, which makes it most economically damaging in leeks, scallions, and chives. Damage to bulbing alliums like garlic and onions is typically the indirect result of leaf feeding – reduced plant health and yield, entry wounds for disease that may reduce storage life – but the larvae can sometimes tunnel into the bulbs as well.
Life Cycle
- Adult Moth — For an image of an adult leek moth, visit the Leek Moth Information Center webpage from the University of Vermont Extension
- Brown moth with black and white speckling
- At rest, white triangle visible halfway down outer wings
- ⅜” long at full size
- Nocturnal and thus unlikely to be seen unless using traps
- Larvae — For an image of leek moth larvae, visit Agriculture and Agri-Food Canada’s page on leek moth (figure 10).
- Slender and yellow with brown heads
- Males have orange/brown spots on their backs
- Grow to ½” long at maturity
- Not hairy
- Pupae — For an image of leek moth pupae, visit Agriculture and Agri-Food Canada’s page on leek moth (figure 11).
- Reddish brown but generally concealed by cocoon
- Cocoon has “cargo net” appearance
- Usually on dead or unhealthy steams or leaves, but sometimes on nearby debris or soil surface
Adults overwinter in allium plant debris and emerge when temperatures reach 50°F. They mate and lay eggs on the underside of allium leaves for about four weeks. Eggs are very small (0.4 mm) and iridescent, making them incredibly difficult to see. Larvae then hatch and feed on leaves. On hollow leaves like onions, they tunnel into leaves and feed from the inside but leave the outer membrane intact, resulting in “windowpane” damage. On flat garlic and leek leaves, they feed on and tunnel through leaves. Young leaves are preferred, so they typically tunnel inward and sometimes downward toward or into bulbs. When larvae reach maturity, they spin their characteristic netted cocoons on leaves to pupate. This cycle continues for a total of three generations per season.
Monitoring
- Windowpaning on Hollow Leaves — For an image of windowpaning, visit the Leek Moth info sheet from Cornell Cooperative Extension
- Larvae chew leaves from inside but do not eat outer layer
- Later generations may tunnel toward base of plant
- Split leaf open to look for larvae and/or frass
- Damage on Flat Leaves — For an image of damage on flat leaves, visit Agriculture and Agri-Food Canada’s page on leek moth (figure 3).
- Chewing on outer leaf surfaces
- Occurs most often in the protected folds of leaves and near new growth
- May also feed on garlic scapes
- Leek Moth Frass — For an image of leek moth frass, visit the Leek Moth Information Center webpage from University of Vermont Extension
- Will be present anywhere larvae have been, near feeding damage
- Remains after larvae have left
If you are growing alliums, use this information to monitor and contact Peyton Ginakes if you find signs of leek moth. The University of Vermont Extension and Ontario’s Ministry of Agriculture, Food and Rural Affairs both have good resources on this pest.
Fertility Reminder! It is time for a final nitrogen application. This last sidedress supports the remainder of garlic’s foliar growth. Do not apply nitrogen after early June because this will prolong foliar growth at the expense of bulb development. Applying 30-40 pounds of actual N per acre is generally recommended at this time. Because recent rain has likely washed out some of the previously applied N, applying the higher 40 lb rate is prudent. For smaller areas, note that the standard “per acre” rate can be converted to square footage as follows: amount per acre ÷ 43.5 = amount per 1,000 sq ft. For this recommended rate,
40 lbs N / acre ÷ 43.5 = 0.9 lb N / 1,000 sq ft
0.9 lb N / 1,000 sq ft ÷ 10 = 0.09 lb N / 100 sq ft
See the New England Vegetable Management Guide for N content of common conventional and organic fertility sources.
Pest and Pathogen Situation
Samples of the possible Botrytis leaf blight infections have been submitted to the UMaine Plant Diagnostic Lab. Symptoms progressed at all scouting locations except one where a fungicide was applied. In all other locations, lesions are now over the 1 per leaf threshold set for Botrytis, as discussed in the last two newsletters.
No insect pests except occasional aphids were observed this week at any scouting locations.
Peyton Ginakes, PhD
Research Associate
University of Maine Cooperative Extension
Highmoor Farm
52 US-202
Monmouth, ME 04259
(207) 933-2100
This project is funded by a Specialty Crop Block Grant through the Maine Department of Agriculture, Conservation, and Forestry. Funding for the Maine 2024 Specialty Crop Block Grant Program was made possible by a grant/cooperative agreement from the USDA Agricultural Marketing Service. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the USDA.
Where brand names or company names are used, it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.
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