Fight the Mite! Post-harvest Control of Eriophyid Mites in Garlic

Progress report for ONE21-406

Project Type: Partnership
Funds awarded in 2021: $24,960.00
Projected End Date: 12/31/2023
Grant Recipient: Cornell Cooperative Extension
Region: Northeast
State: New York
Project Leader:
Crystal Stewart-Courtens
Cornell Cooperative Extension
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Project Information

Project Objectives:

This project seeks to evaluate the effectiveness of the predatory mite Stratiolaelaps at controlling populations of dry bulb mite Aceria tulipae in garlic in a variety of different storage environments. By choosing five commercial garlic farms with different drying and storage conditions we hope to find the ideal range of conditions to allow Stratiolaelaps to maintain viability for long-term A. tulipae control while also keeping damage below environmental thresholds. 

Once we have successfully developed a protocol for the use of Stratiolaelaps in storage we will present our findings in newsletters in Vermont and New York, reaching over 1500 growers. We will also present our findings at conferences throughout the northeast and at garlic schools, reaching hundreds of growers. Combining this information with other emerging information about season-long A. tulipae management should allow growers nearly complete control of a pest that can reduce yields by up to 23%.


The eriophyid mite Aceria tulipiae, commonly known as dry bulb mite, has been documented in garlic crops in the United States since 1938 (Keifer 1938) and is considered the main pest in garlic in all production areas around the world, causing average losses of 23% (Larrain 1986). We have been documenting dry bulb mite damage since 2017 in New York (Stewart 2017), 2016 in Massachusetts (Madieras 2016) and most recently in Maryland (Brust 2021). Based on discussion with pathologists and extension educators throughout the region during our 2020 weekly pest calls it is assumed that dry bulb mites are a widespread problem throughout the Northeast. 

Dry bulb mites can cause significant damage to garlic crops in storage and in the subsequent growing season.  In storage each generation takes just 8-10 days to develop at room temperature (Courtin et al, 2000). Damage in storage presents as shriveled cloves and increased secondary disease incidence. Heavily infested garlic that is replanted may die from secondary diseases over the winter or may emerge with stunted, twisted, and yellowed foliage resembling viral infection. Garlic often grows through minor infections but may harbor enough mites through the season to start the cycle again in storage. 

Work is ongoing to determine organic and conventional treatments that suppress mites from planting through the growing season through an NYSCBG project. An ongoing SARE-funded post-harvest study (ONE-19-351) is examining the effects that drying and storage temperature and relative humidity have on post-harvest diseases and eriophyid mite infestations. The final piece of the puzzle is to determine whether it is possible to combat mite infestations in storage using biological controls. We specifically propose deploying Stratiolaelaps mites in garlic storage bins, an approach trialed in Holland on lilies with positive results (Lesna et al, 1995). As with many challenging pests, control of dry bulb mites will require an integrated approach including control measures during all crop stages. Reducing mite infestations is essential to keeping garlic seed quality high for on-farm use and for the success of the garlic seed industry. 

New York is the fourth largest producer of garlic in the United States and the seed source of choice for the Northeast and the Midwest, as it is better adapted than garlic from the West Coast. Garlic is grown on over 800 farms in New York, mostly in small acreages that follow low-input or organic practices. The New York garlic industry has expanded to approximately 382 acres in 2017 (Census of Agriculture), and 20% of all New York vegetable farms report growing garlic, which is more than broccoli, cabbage, lettuce carrots or onions.  The value of New York garlic production is not well defined.  However, assuming yields of 10,000 to 16,000 lb per acre and a conservative price of $9.00/lb, the industry is worth between $34 and $55 million annually. Notably, garlic growers in Vermont and Maine are also expanding seed production, and we expect garlic acreage to continue to expand as a result. 


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Materials and methods:

This project was be implemented on four commercial garlic seed farms, each of which provided a complete picture of their mite management strategies through self reporting of conditions in both drying and storage environments. The farms we partnered with are geographically diverse, located from eastern NY through VT, and use different cultural practices for drying and storage. Each site will be treated as a replication when doing a analysis of the four farms, and we will also allow each farm to be analyzed independently by creating five replications of the treatment and control at each farm in which bulbs (5) will be samples and cloves (25 or more)  are sub-samples. This robust experimental design should provide us adequate information to develop solid recommendations on predatory mite release for dry bulb mite control. 

The protocol is designed to test the hypothesis that Stratiolaelaps predatory mites can be deployed in storage to significantly reduce A. tuplipae levels. 


Update: We were not able to secure the dataloggers needed for this step, and are instead relying on self-reporting.

At harvest: researchers will visit each farm and install an Onset temperature and relative humidity sensor/datalogger in the drying facility. Censors will be protected from direct sunlight and located as close as practical (example: on the bench with garlic in a drying tunnel) to the garlic. Data will be collected from harvest through movement to storage. 

In storage: Researchers visit each site when the farmers are ready to move garlic from the drying area into the storage area. They will note any cleaning steps that growers take at this point, including removal of roots, dirt, and stems, and will set up the experiment deploying predatory mites within the storage area:

  1. We used a Randomized Complete Block Design, whereby randomly assigned garlic will be assigned to an untreated control of garlic alone (with no predatory mites) or an experimental treatment of garlic and predatory mites at a rate equivalent to 1 liter per 1000 square feet.
  2. Treatments were applied by placing 50 bulbs, all of uniform size and not showing obvious physical damage, into organza bags (
  3. Five control bags and five experimental bags, each containing 5 bulbs, were stored at each of the five farms, distributed throughout the commercial storage area.  
  4. Variety selection: Three of the farms used Porcelain varieties (German white or Music), and one used a Rocambole (Killarney Red), which was believed to be more susceptible than the Porcelain varieties.
  5. Experimental bulbs were mailed to PI for final assessment protocol:
    1. Assess all bulbs from each treatment and record and separate any which have deteriorated due to unrelated post-harvest diseases, such as penicillium or botrytis
    2. Each remaining bulb is assessed using the following protocol:
      1. Separate all cloves, peel, and rate individual cloves by bulb for both fusarium level and bulb-mite damage level
        1. Fusarium rating is by % of clove covered in lesions
        2. Bulb mite damage rating is completed using a pictorial benchmark on a scale of 1-5
        3. One clove per bulb is randomly selected for A. tuipae counting at 40X magnification. 

Analysis: Each of the 4 sites will be analyzed using a paired t-test to examine effectiveness of the experimental treatment. At each site,  each bag is a separate replication, and the 5 individual bulbs are samples while cloves are subsamples. Data from the five sites will be analyzed using an Analysis of Variance after an assessment of data by the Cornell Statistical Consulting Unit to ensure data are correctly transformed. The second analysis will give us a sense of which environmental conditions are most conducive to A. tulipae control using Stratiolaelaps.

Research results and discussion:

Garlic remains in storage currently with the goal of completing data collection by February 1st, 2023. During an initial inspection in November 2022, bulbs remained firm and unblemished. We believe that longer term storage will provide needed time for mite and disease development, with all samples being held in identical conditions.

We were unable to obtain WNY samples, primarily because of logistical issues with mite distribution. The mites can only be stored in their packing materials for about a week, 3 days of which were used by transit from Canada to the PI's address. Distribution to Vermont and Eastern Ny was all we were able to achieve in that time frame.

Research conclusions:

No conclusions yet.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

Information from this project will be shared with growers in an article featured in the following newsletters: 

ENYCHP’s Produce Pages (574)

CCE CVP’s VegEDGE (650)

Vermont Vegetable and Berry Growers Association Newsletter (700)

We will also present about the results of the project at the following winter meetings:

NOFA-NY (100 attendees)

New England Fruit and Vegetable Conference (75 attendees)

New York garlic schools (100 attendees)

Vermont Vegetable and Berry Growers Annual Meeting (200 attendees)

Learning Outcomes

Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

This work has not been completed yet.

Project Outcomes

Project outcomes:

Not completed yet.

Assessment of Project Approach and Areas of Further Study:

Not completed yet.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.