Cooperative Extension at Highmoor Farm

Garlic IPM Newsletter No. 6 — June 4, 2026

Much of Maine has enjoyed a nice stretch of warm and dry weather heading into the weekend. Garlic is developing nicely at all scouting locations. The NEWA onion disease forecast remains clear for Maine locations through June 9, but keep in mind that this updates with the weather forecasts, which have been erratic. Check these forecasts regularly if you are using them to time scouting efforts (as for Botrytis leaf blight and Alternaria purple blotch) or initial prophylactic controls (as for onion downy mildew), after which a 7-10 day spray schedule should be maintained. Rotate FRAC codes with every application to manage resistance. The New England Vegetable Management Guide offers a good starting list of controls, and this Cornell “cheat sheet” displays efficacy results from their latest fungicide trials in onion. Cultural management options focus on minimizing leaf wetness by controlling weeds, so as to improve airflow in the crop, and refraining from overhead watering.

Botrytis leaf blight lesions have levelled off in all but one scouting location (Washington). However, leaf tips are beginning to take on a “dirty” appearance at all scouting locations to varying degrees, which is typically the result of Alternaria purple blotch (PB) or Stemphylium leaf blight (SLB) sporulation. These pathogens are fairly ubiquitous in allium plantings, and readily colonize the weak or dying tissues of leaves as they die back. This may not represent a major economic risk to garlic crops. Still, controls in garlic may be warranted if other alliums are nearby, since severe foliar infection in onions can reduce yield and prevent proper lodging, resulting in bulb rots.

Onion Thrips Update

Low numbers of onion thrips have been found in Monmouth, as expected based on the growing degree day model. Sufficient GDDs have accumulated for thrips to emerge in southern Maine, from Kittery north to Newry, Farmington, Augusta, and Damariscotta. Next week’s newsletter will discuss onion thrips biology, crop damage, and management in more detail.

The table lists GDDs from Maine Climate Office website and numbers marked with an asterisk (*) indicate that sufficient GDDs have been met in that location for onion thrips to emerge, and regular scouting is warranted.

Now is the time to look out for leek moth

We are continuing to monitor for leek moth around the state and have yet to find any signs of this invasive pest. However, since leek moth has already been reported in New Hampshire this year, it is advisable to keep an eye out for it, especially in western Maine. Adult moths emerge in spring when temperatures reach 50°F and lay very small eggs on allium leaves – often garlic, since it is one of few alliums in the field at this time. When larvae hatch, they feed on and mine through leaves and sometimes scapes; this feeding damage is often the first sign of this pest since the moths are nocturnal. In onions and other alliums with hollow leaves, feeding from inside the leaves creates a “windowpane” effect since larvae do not eat the outermost layer. Larvae continue to feed for about 2-3 weeks before pupating in cocoons that look like cargo nets.

Larvae

• Larvae are slender and pale yellow with brown heads; up to ½” long; not hairy
• Males have brown spots on backs
• May also feed on scapes
• For more information on larvae feeding damage, please check out MOFGA’s page on Leek Moth.

Windowpane Damage

• Larvae feed from within hollow leaves, leaving only the outer leaf layer intact
• Split open affected leaves to look for larvae and frass (excrement)
• For full-color and close up pictures of windowpane feeding damage on hollow leaf, visit the Leek Moth Damage, Monitoring, and Detection page from University of Vermont Extension.

Pupae

• Pupae are reddish brown
• Often on dead/unhealthy leaves, but sometimes on nearby residue or soil
• Pupate for 2-3 weeks
• 2-3 generations per year
• For full-color picture of pupa in cargo net cocoon, visit An Integrated Approach to Management of Leek Moth: 10 years of collaborative research, development and knowledge transfer webpage from Agriculture and Agri-Food Canada.

While feeding on scapes renders that portion of garlic unmarketable, leek moth is not a major economic pest of bulbing alliums since bulb size and quality is typically not impacted. However, the fall generation larvae tend to tunnel from the growing point downward, and therefore is most damaging in leeks where the mined leaves become unmarketable. Additionally, if larvae are brought into curing or storage areas on garlic or onion tops, damage to bulbs can occur. If you see any feeding damage or pupae that may be leek moth, please preserve the plant and/or insect material and contact Peyton Ginakes by email at peyton.ginakes@maine.edu. For more information about this pest, the University of Vermont and Ontario’s Crop IPM program are great resources.

Peyton Ginakes, PhD
Research Associate
University of Maine Cooperative Extension
Highmoor Farm
52 US-202
Monmouth, ME 04259
(207) 933-2100

peyton.ginakes@maine.edu

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.

University of Maine Cooperative Extension is an equal opportunity institution and provider committed to nondiscrimination. For more information, visit extension.umaine.edu/nondiscrimination.