Garlic IPM Newsletter No. 11 — June 26, 2025
Thrips
Thrip Pressure Still Low
Onion thrips counts remain low despite dry, hot days and no scouting locations have yet reached the 1 thrips/leaf threshold. Warm temperatures drive development and the speed at which new generations arise. Nearly all Maine locations have accumulated enough growing degree days (140 GDD52.7ºF) for the overwintering generation to emerge. From there, each generation requires about 323 GDDs to complete its life cycle. This past week of extremely hot temperatures may result in a population boom, while possible rain over the weekend may drive numbers down. Phenological tools give us clues about when to pay attention, but continuing to scout is the only way to know when controls will be warranted.
| Scouting Location | Thrips (per leaf) as of June 24, 2025 |
|---|---|
| Buxton | 0.07 |
| Monmouth | 0.15 |
| Topsham | 0.01 |
| Washington | 0.13 |
Fusarium Bulb, Basal Plate, and Clove Rots
Fusarium is a fungal pathogen that can negatively affect garlic and other alliums in multiple ways. Typically, cloves become infected through the seed (or “basal”) plate by soil or surrounding debris, or even through irrigation water. They may be non-symptomatic, which can make controlling spread difficult. Various symptoms may appear, depending on when conditions become favorable for infection and perhaps which Fusarium species are present.
- Cloves: Symptoms on infected cloves usually appear as sunken brown lesions; these should not be used as seed stock. When infected cloves are planted, they may rot before they germinate in spring or shortly thereafter. Storing cloves at 40°F will reduce lesions.
- Early Growth: Distorted early growth may result from Fusarium since the basal plate is where new tissue develops. Leaves may be curled and stunted, and plants may fail to continue growth.
- Plant Yellowing: Premature plant yellowing (starting at the tips), wilt, and death are not uncommon symptoms of infection. This occurs when infection at the basal plate decays the root system and/or spreads to the neck of the plant. This tends to appear during hot conditions, since plant demands are high but cannot be met by the rotten tissue.
For a close up photo of Fusarium lesions on a garlic clove, Oregon State University Extension has an information sheet, Fusarium rot of garlic bulbs, with clear images.
If your garlic plants or cloves show these symptoms, it is worth sending a sample to the UMaine Plant Diagnostic Lab for confirmation. Plants and debris should be removed from fields with infected plant material, and those areas should be rotated out of alliums for at least 4 years. Tools may also harbor this pathogen, so good sanitation is important for minimizing spread. Excess nitrogen favors Fusarium infection and abiotic stresses may exacerbate symptoms, so fine tuning fertility and irrigation may reduce losses.
NOTE: There will not be a newsletter next week; keep scouting and stay tuned for the July 10 issue.
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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