Eriophyid Mites in Garlic

After harvesting garlic, usually around November, stored garlic cloves may take on a frosted, sparkling appearance. The effect is similar to ice crystals on a window. If you notice this on your garlic, it is most likely the result of Eriophyid mites.

There are over 1500 species of Eriophyid mites belonging to the family Eriophyidae. Many are pests in vegetable and fruit production as well as the ornamental landscape. For example, russeting on pears, the transmission of rose rosette virus, hackberry witches broom, and distortion of elderberry leaves are the result of different species of Eriophyid mites.

The frosted appearance of garlic cloves from Eriophyid mites can result in unmarketable bulbs and decreased shelf life. Unfortunately, it is not well known whether replanting these cloves as seed will contribute to mite populations the following season. The population dynamics of Eriophyid mites in garlic plantings is not well understood. Similar to spider mites, the presence of Eriophyid mites in garlic may be correlated to drier seasons. Observations communicated by Dr. Frank Hay at Cornell are that during dry years, the mites may be looking for moist sites to inhabit. The inside of the garlic bulb presents a hospitable location. Alternatively, wetter years may simply inhibit mite presence. For the grower, this means that soil moisture and attention to irrigation, especially during a dry season, could be helpful in reducing the presence of Eriophyid mites in garlic.

Avoiding mite infestations in-season is critical to reducing losses post-harvest. Very little research has been conducted on the efficacy of cleaning garlic bulbs after harvest to remove mites and reduce marketable losses. However, because the importance of mite introduction into the field from infested seed is not well understood, the grower could potentially recoup losses by cleaning the seed and planting it for next year's production. Effectively cleaning the clove without inducing phytotoxicity would be key to limiting the potential for introduction into the field. The following information is specifically for garlic being used for seed and not going to market.

Dr. Hay has conducted a small-scale experiment to test the efficacy of several products in reducing populations of Eriophyid mites on infested garlic. Of the products tested, a 1% (v/v) solution of a Potassium Salts of Fatty Acids product (49.00% a.i.) was most successful and reduced mite populations on 80% of the treated cloves. It is important to note that this only reduced the population, and egg viability was not tested.

Soaking cloves in a 20% bleach solution for 20 minutes has been observed to reduce bloat nematodes and not cause phytotoxicity to the clove (Roberts and Matthews 1995). These methods have not been tested for Eriophyid mites, but concentrations above 25% bleach have been shown to reduce seed viability. Please refer to product labels for methods of use. The label is the law.  

References

Roberts, Philip and Matthews, W. (1996). Disinfection Alternatives for Control of Ditylenchus dipsaci in Garlic Seed Cloves. Journal of Nematology. 27: 448-56.

Davis, R. and Beddes, T. (2011) Eriophyid Mites: Bud, blister, gall, and rust mites (PDF). Utah State Extension.

Thank you, Dr. Frank Hay, for sharing your observations and results.