Garlic IPM Newsletter No. 13 — July 17, 2025
Garlic Season Wrapping Up
Garlic harvest has begun at one southern Maine scouting site and will follow in other sites over the next week or two. This newsletter will provide a re-cap of the season and some information on what to look out for as you go about harvesting and storing your crop.
Foliar Pathogens
The persistently wet spring conditions led to an early occurrence of Botrytis leaf blight at several scouting locations, but timely fungicide applications (in combination with drier, warmer weather) provided control for this particular foliar pathogen. Purple blotch/Stemphylium was later found at several locations as well, but did not appear to impact overall production as infections were primarily on dead leaf tips. Onion downy mildew was not observed in our garlic scouting this season.
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- Botrytis leaf blight on garlic; photo by Peyton Ginakes, UMaine Cooperative Extension
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- Purple blotch and/or Stemphylium on garlic; photo by Peyton Ginakes, UMaine Cooperative Extension — Purple blotch (Alternaria porri) and Stemphylium leaf blight are only distinguishable by diagnostic services, but effects on plants and management methods are the same. Stemphylium generally arises later in the garlic season as a secondary pathogen on tissue that is already dead or dying back.
One disease that made a late appearance this season and that hasn’t yet been mentioned in this newsletter is anthracnose, caused by Colletotrichum fioriniae. Warm recent weather seems to be ideal for this pathogen’s growth, and it has been observed more frequently than usual on garlic this year. Typically this only really affects scapes, but several samples collected this season had anthracnose along the plant stem and perhaps bulb. More information on anthracnose in garlic can be found in this Cornell University resource.
Best practices for disease management include proper residue and weed management. All residue, culls, and host weeds should be destroyed via deep burial or thorough composting. Crop rotation will minimize the risk of pathogen carryover to next year.
Insect Pests
Onion thrips were the only major insect pests we found on garlic this season. While to many of us it has seemed like a very hot few months, which is favorable for thrips, there have been occasional stretches of cool weather that seemed to slow their development. Thrips are now over threshold in Monmouth but not other scouting locations. Thrips can reside in the bulb and cloves and become especially problematic in planting stock, so thrips control through harvest is important. When harvesting infested garlic, separating and disposing of tops from the 6-8″ trimmed bulbs may help to reduce the number of thrips that end up the stored crop. Beyond garlic harvest, thrips will keep feeding on other alliums (and brassicas), so continued scouting is prudent.
Two major invasive pests of concern, leek moth and allium leafminer, have still not been confirmed in Maine. Many other New England and Canadian neighbors are reporting problems with these pests (including several bordering New Hampshire counties), so please continue to scout alliums and contact Peyton Ginakes with suspicious signs or symptoms.
Seed Testing
Seed garlic testing is offered by the University of Maine’s Plant Diagnostic Lab (scroll down for the garlic seed test info). This is recommended for any garlic intended for use as seed stock that looked less than ideal at harvest. Several companies that sell seed now require negative test results from farmer suppliers to ensure their products are free of several major seedborne pests and pathogens.
Bloat nematode is a notable pest that is included in this test, since it is primarily spread through seed and can be very devastating. Affected plants may be stunted and yellowed, and bulbs may be distorted, bloated, brown, and have missing roots. More information on this pest is available in these UMaine and UMass Extension resources.
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- Bloat nematodes can feed on roots, resulting in the absence of some or all roots at the basal plate; photo by Steve Johnson, UMaine Cooperative Extension
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- Bloat nematode feeding within bulbs results in distortion and swelling, or a “bloated” appearance; photo by Steve Johnson, UMaine Cooperative Extension
Garlic afflicted with bloat nematode, or grown in fields with plants that have tested positive for bloat nematode, should not be used or sold as seed stock. Be sure to follow sampling instructions on the submission form when collecting plants for testing.
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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