Garlic IPM Newsletter No. 7 — May 29, 2025
Fungal diseases remain the primary concern this season due to continuously wet conditions. Botrytis leaf blight in particular is increasing in prevalence at all scouting locations, and the weather forecast warrants action for those using fungicides. As a reminder, the action threshold for the first fungicide application is when:
- Lesions average 1 or more per leaf. Inspect ten groups of three plants each, counting the number of leaves and lesions on each to find the average per leaf (not plant). At our four scouting locations, we are finding 1.2 to 7.9 lesions per leaf on average – all of which are over threshold. Scout your plants to track lesion development.
- The Modified Blight Alert IPI on NEWA for your location is 7 or greater. This number is a measure of how conducive environmental conditions are for botrytis development.
- Chances of rain are 30% or greater. Check NEWA or your local weather forecast and apply a fungicide before upcoming rain events.
Fungicide protection is lost within 7 days or 1″ rain, after which coverage should be maintained based on the IPI and continued development of the disease in your field. Actively manage botrytis when the IPI is > 7 for 5-7 days of the forecast.
Insect Pests
Much of Maine has now accumulated sufficient GDDs for onion maggot to emerge (390 GDD40), and many locations in southern and midcoast Maine are reaching peak flight. If this pest has been problematic in your area in past years, protect your allium crop with row cover. Peak flight of the overwintering generation occurs at 735 GDD40 – wait to remove row covers until one month after this since adults can live for 2-4 weeks. Track GDDs in your area on the Maine Climate Office page.
No onion thrips have yet been found at any scouting locations, and are only starting to be seen as far north as Massachusetts. Thrips hatch at 140 GDD52.7 – these GDDs can also be tracked on the MCO page. Fryeburg, Kittery, and Sanford will likely surpass this threshold within the next week, but since thrips thrive in hot and dry weather, the wet forecast will work to those growers’ advantage in the short term.
There have been no signs or reports of leek moth or allium leafminer thus far in Maine. Remember to keep an eye out for leek moth and report any signs of this pest to Peyton Ginakes. Collect photos and plant samples when at all possible. Learn more about allium leafminer below.
Allium Leafminer
Like leek moth, this is another insect pest to be on the lookout for. While it has not been found in Maine, it was first detected in the US (PA) in 2015 and has since spread as close to Maine as New York and Massachusetts.
Pupae overwinter in soil or in plants, and emerge early in spring (350 GDD33.8). ALM adults lay eggs on allium crops, leaving a series of circles on leaves – its most recognizable sign. When larvae hatch, they mine downward toward the base of plants and pupate either in the plant or nearby soil. Adults emerge in fall, constituting the second generation. Damage from the spring generation is limited to plants with sizeable leaves at the time of emergence: chives, ramps, scallions, ornamental alliums, and garlic. Those alliums harvested before the fall (September) generation emerges are low-risk; leeks, chives, scallions, and ornamentals remain high-risk.
While the ovipositing marks can decrease quality of allium crops with marketable leaf components (chives, spring onions, ramps), the primary damage inflicted by this pest is the larval mining. Destructive in and of itself, this feeding also invites disease and pupae may remain in leaf sheaths and plant bases/bulbs.
UMaine Cooperative Extension and the Maine Dept. of Agriculture, Conservation, and Forestry are monitoring for the presence of this pest. To help with this effort, look for signs of ALM in your allium crops and contact Peyton Ginakes if you see signs of this pest. Adult flies are small, (0.11″ long), have an orange/yellow spot on their heads, and yellow “knees”. Oviposition marks on leaves are the easiest signs to look for. Pupae are 0.11-0.15″ long, reddish brown, and leave feeding mines in leaves and between leaf sheaths.
For more information, see additional resources from and Penn State Extension, Cornell AgriTech and UMass Extension.
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.
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