Postharvest Handling of Garlic for Control of Pests and Disease

Garlic growers have improved their growing techniques and drying techniques through support from previous research projects funded by SARE and other granting agencies. A remaining challenge for growers is storage of their crop either until planting or for sale at winter markets. Often, garlic that is of poor quality coming out of storage appeared healthy and in good condition after drying. Key storage issues include Fusarium, Botrytis, and the recently identified Eriophyid mite. Losses out of storage can be devastating and sometimes almost the entire crop is lost (grower reports; team farm visits).

New York is the fourth largest producer of garlic in the United States with the highest producing states all on the West Coast.  New York is also the seed source of choice for the Northeast and the Midwest, as New York-grown garlic performs better in these regions than seed produced on the West Coast. Garlic is grown on approximately 400 farms in New York, mostly in small acreages that follow low-input or organic practices and primarily supply niche local markets. The New York garlic industry has expanded tremendously from only 11 acres in 1992 to approximately 300 acres in 2012 (Census of Agriculture), and 10% 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 $27 and $43 million annually.

In 2018, the project PI and a garlic grower implemented very different post-harvest practices on garlic from one seed lot grown in the same field prior to planting. Garlic handled by the team was of excellent quality, while the grower’s garlic was dehydrated with loose wrapper leaves and had some Fusarium. The practices differed in stem length, curing environment, and storage environment, so it isn’t clear which step in the postharvest process made the difference. These findings demonstrate the effects that postharvest practices have on garlic quality warranting further research.

The effects on garlic quality of storage conditions alone or the combined effects of curing and storage post- harvest practices are not well understood. We know through dozens of farm visits where storage is a problem that issues appear to arise unexpectedly, and a grower who has had excellent quality in past years can have a bad year with significant losses despite not making any changes to systems or practice. Because many drying and storage systems are passive, weather and associated temperatures and relative humidity seem to be significant factors. In order to justify improved environmental control systems, we need clear results indicating which environmental conditions lead to predictable success.

Since 2011, the project PI has been leading work on garlic production, with projects addressing garlic bloat nematode (ONE 11-149), post-harvest handling (LNE 12-319), fertility, and most recently Fusarium disease management (LNE 16-353). During the Fusarium project, the garlic team observed that Fusarium diseases of garlic appeared to be part of a complex, often acting as a secondary pathogen following injury by another fungus, environmental stress/damage, or insect/nematode feeding. In 2016, the garlic team identified another pest of garlic that was often associated with Fusarium, the Eriophyid mite, which caused severe clove dehydration in storage and lead to substantial crop losses on several farms. Very little is known about the lifecycle, or how to manage this newly rediscovered pest in New York.

The field-based Fusarium management study has taught us that successful suppression of this disease is based on an integrated approach which minimizes injury, promotes plant health, and avoids environments conducive to disease. There are still unanswered cultural control questions which we will continue to pursue, but post-harvest quality management, particularly in storage, is now the most significant issue still facing the garlic industry.

Basic guidance related to postharvest handling of garlic indicates a field drying step just following lifting is helpful to minimize mechanical harvest and handling damage.  After this step, a more complete curing step is suggested, but often with very little guidance about the conditions to follow (Gross, 2014). Some producers follow the guidance for onions (80 F, 70-80%RH, with air flow to ventilate), but variably so. Often, the level of effort is low and the level of control is also.

More recent research points to the benefit of a high temperature curing step (Abd-el Rahman, 2009). This approach utilizes heated air and improved RH control to expedite the curing process and improve the quality of the cured leaf laminate (Eshel et al, 2014).  The impact of these processes on diseases and pests which proliferate in long term storage is not well described.  Currently some growers in the northeast are using high tunnels to increase heat and decrease relative humidity during drying based on positive research results (Stewart 2013), but this passive system may still be contributing to long term storage issues. Ventilation is typically focused on mixing the air in the space, not always providing adequate air exchange with outside air, and almost never provides air flow through the curing bed of product. It is likely that there are microclimates of high temperature and high humidity in the areas closest to the curing bulbs and the impact of this deviation in environmental condition is not clear.  Additionally, this step is usually carried out in spaces with large diurnal swings in temperature and humidity which may also have a role in the quality of the resulting bulbs.

The project co-PI from UVM Extension, Chris Callahan, has also been focused on postharvest handling of various crops of economic significance to the region.  In an earlier SARE grant (ONE13-176) he formalized a curriculum around storage for farmers and processors.  This work helped to translate existing evidence-based knowledge from larger volume production regions into practitioner-focused workshop events and associated resources to improve long-term storage conditions of various crops including garlic. This work highlighted the need for focused work on curing and precooling which materialized as a later SARE project (LNE16-347).

Post-harvest management of Fusarium disease has been extensively studied in grain crops, with work in wheat and corn demonstrating methods to eliminate Fusarium in storage. A study in field corn eliminated Fusarium from seed through sealed storage at both 86°F and 10% seed moisture for 10 months and at 77°F with 14% seed moisture for 6 months (Kabeer et al, 2007). 77° F is considered within the range of optimal short-term storage for garlic; what is not clear is how this affects Fusarium in higher moisture garlic seed.

Eriophyid mites, specifically Acerius tulipae, has been identified as a world-wide pest of garlic and has been specifically studied in other production regions. Work conducted in south-western France on growth rates on green garlic leaves indicates that the optimum temperature for development is 25°C and 100% relative humidity. At these conditions, mites develop from egg to egg in about 20 days. As relative humidity drops below 75% and temperatures rise above 30° C, egg mortality increases. 45° C for just one hour leads to complete egg mortality, and temperatures below 6° C pause development (Courtin et al, 2000). This work needs to be replicated on storage garlic.

CITATION LIST

Abd-el Rahman, M. M., & Ebeaid, M. T. (2009). Some Factors Affecting Artificial Curing of Onion Bulbs and its Effects on the Storability. Misr J. Ag. Eng - Process Engineering, 26(2), 905–921.

Courten, O; Flauvel, G; and Leclant, F. Temperature and relative humidity effects on egg and nymphal development of Aceria tulipae (K.) (Acari : Eriophyidae) on garlic leaves (Allium sativum L.). Ann. appl. Biol. (2000), 137:207—211

Eshel, D., Teper-Bamnolker, P., Vinokur, Y., Saad, I., Zutahy, Y., & Rodov, V. (2014). Fast curing: A method to improve postharvest quality of onions in hot climate harvest. Postharvest Biology and Technology, 88, 34–39. https://doi.org/10.1016/j.postharvbio.2013.09.002

Gross, K. (2014). USDA Handbook 66: The Commercial Storage of Fruits, Vegetables, and Florist and Nursery Stocks. Retrieved from https://www.ars.usda.gov/ARSUserFiles/oc/np/CommercialStorage/CommercialStorage.pdf

Kabeer, F; Hill, M.J.; and Hampton, J.G. Effect of maize seed storage conditions on the survival of Fusarium spp. Seed Science and Technology Vol 25, p. 329-332. 1997.

Mann, L. (1952). Anatomy of the Garlic Bulb and Factors Affecting Bulb Development. Hilgardia - A Journal of Agricultural Science Published by the California Agricultural Experiment Station, 21(8), 195–231.

Stewart, C. (2013) Garlic post-harvest trial results. New England Fruit and Vegetable Conference Compendium, p. 122-124. https://rvpadmin.cce.cornell.edu/uploads/doc_773.pdf

Stewart, C and Hay, F.S. (2017) Eriophyid mite: Micro-scourge of garlic. Produce Pages, Vol 3 issue 4, 12-14. https://rvpadmin.cce.cornell.edu/uploads/doc_774.pdf