Garlic IPM Newsletter No. 2 — April 24, 2025

April 24, 2025 Garlic IPM Newsletter

Managing Garlic Fertility

Garlic is a moderate to heavy feeder, and careful nutrient management will aid plant development while mitigating the risk of foliar infections. The first step in any fertility program is testing your soil before planting. You can find more information about soil tests and their interpretation in this bulletin.

The table below, from the New England Vegetable Management Guide, shows nutrient recommendations for garlic. Phosphorus and potassium applications rates should be chosen based on your soil test results. The nitrogen (N) recommendations below are for quick-release sources to ensure that plant-available N is sufficient at specific growth stages.

Image of table from New England Vegetable Management Guide regarding nutrient recommendations for garlic which can be found online at https://nevegetable.org/
Source: New England Vegetable Management Guide
Close up of garlic plant 8 inches tall and yellow leaf tips.
Signs that it is time for first spring N application: garlic nearly 8″ tall (A), and yellow leaf tips (B). Photos by Peyton Ginakes, UMaine Cooperative Extension. (Click photo to enlarge).

Split-Applying N

Nitrogen encourages foliar growth. Frontloading all of a garlic crop’s required N in fall will result in excessive fall growth and loss of remaining N before growth resumes in spring. Instead, split N applications are recommended.

  1. Pre-plant: Applying about 1/3 of the total N needed before planting will provide the crop with a sufficient start.
  2. Shoots at 6 inches: Now! At this stage, garlic needs a nitrogen boost for foliar growth, but applying too much all at once may lead to excessive top growth that can become fodder for foliar diseases. Apply approx. 40 lb N.
  3. 3-4 weeks later: This final sidedress will support the last of the foliar growth before plants shift their energy to bulb development. Do not apply N during the crop’s final month, as this can prolong foliar growth and thereby delay bulb enlargement. This can also make plants more susceptible to disease.

In fields with especially high organic matter, 20-30 lb N at each application may be sufficient. Nitrogen sources should be quick-release – fertigate with soluble fertilizers or broadcast/band inorganic granular fertilizers. If using a source that is slower to mineralize, adjust timing to synchronize release with the schedule outlined above.

 

Pest Situation

No pests or diseases were observed at any farms where we scouted this week, which was expected based on environmental conditions. Here is a quick overview of what to look out for and when, using forecasting tools:

  • Onion Maggot: Overwintering generation begins to emerge at 390 GDD40°F – use Maine Climate Office GDD maps (base 40) if your location is not well represented in NEWA.
  • Onion Thrips: Eggs hatch at 140.4 GDD52.7°F – in NEWA, use GDD base model 10.4°C since it is the closest conservative estimate to 52.7°F.
  • Leek Moth: Adults emerge when temperatures reach 50°F, but leek moth has not been confirmed in Maine since 2021. Traps are present throughout the state to monitor for this pest.
  • Allium Leafminer: Adults emerge at 350 GDD1°C – use the NEWA 1°C base model starting Jan 1. However, like leek moth, ALM has not been confirmed in Maine and we are monitoring for it throughout the state.
  • Fungal pathogens: This NEWA tool estimates favorabilty of environmental conditions for the development of three fungal pathogens: downy mildew, purple blotch, and onion botrytis. Instead of GDDs, it is based on current and forecasted temperature, precipitation, and humidity.

As a point of reference, current GDDs are shown in the table below for Lewiston, ME. Based on this information, you can see that insect pests we are likely to see in Maine need more time to develop, and this week’s forecast mostly precludes the development of fungal pathogens. Future newsletters will discuss these pests in more detail.

Growing Degree Days for Relevant Insect Pests, April 24, 2025
Pest Target GDD Apr 24 Gdd Accumulation in Lewiston, ME
Onion Maggot 390 GDD40ºF 131
Onion Thrips 140.4 GDD52.7ºF 9 (GDD10.4ºC)
Allium Leafminer 350 GDD1ºC 175

 

Pie graph showing that 54% of the garlic newsletter recipients save their own seed, 25% buy from farmers, 17% buy from seed companies and 4% answered they obtain their garlic seed from other sources.

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.

The University of Maine System is an equal opportunity institution committed to nondiscrimination.