November 8, 2011

Nematode Threatens Garlic Industry

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A recent nematode outbreak is threatening New York’s $24.5 million garlic industry. The pest, Ditylenchus dipsaci, has over 100 vegetable hosts and has shown up in soil tests to be present in 17 New York counties to date.D. dipsaci was first identified by Christine Hoepting, an extension vegetable specialist within Cornell Cooperative Extension, in June 2010.According to Amy Ivy of Cornell Cooperative Extension, the term nematode is very broad, as some are beneficial, while others are not. D. dipsaci have detrimental effects on garlic.Potential signs of this bloat nematode infestation include stunted growth, yellowing of leaves that may droop and fall, as well as softening, discoloration, and cracking of the bulb.“Because [nematodes] are microscopic, it can be hard to know if they are present or not,” Ivy said.Prof. George Abawi, plant pathologist at the New York State Agricultural Experiment Station in Geneva, N.Y., is currently researching the extent to which the nematode infestation has spread, as well as determining which seed cleaning methods are most effective, to avoid further contamination. Abawi is currently only scientist in New York with the ability to test garlic and soil samples for D. dipsaci.Garlic bulbs house several separate cloves, each of which, if planted, will give rise to a new garlic plant. As a result, growers often save garlic harvests to share with others for replanting.“Garlic growers sometimes exchange seed, and that has been the main way that the pest has been distributed [through contaminated cloves]… we are trying to stop that from happening, and help growers buy clean seed,” Abawi said.Abawi noted that even while kept in storage, the nematode can continue to feed and reproduce in the cloves.According to Lucy Garrison-Clauson of Stick and Stone Farm, buying garlic seed from a seed company is not economical, costing upwards of $10 to $15 a pound.“You always take a risk in trading seed with other growers,” she said. “We planted seed that had a fungal disease that contaminated our soil and can stick around for like, 30 years. We used to grow a lot of garlic, but now garlic is a small part of our operation.”“Many garlic gro wers are very frustrated,” Ivy said. “[The bloat nematode] is very easy to unwittingly spread; this is all very new to garlic.”While a bloat nematode outbreak such as D. dipsaci has not been seen before in garlic, onion industries in the 1940s battled a similar pest.A member of the allium family along with garlic, onions were long ago planted and grown from “sets,” very small, young onions propagated specifically for replanting.“Harmful nematodes lived in these sets just like they are living in the garlic cloves today. Onion growers dealt with the pest by fumigating the soil and using powerful chemicals to kill the organisms in the soil. Nowadays all onions in big production in New York are grown from seed [rather than from sets],” Ivy said.To help fund Abawi’s research on the garlic nematode and how growers can avoid it, he recently received a $69,122 grant from the New York State Department of Agriculture and Markets. This research will include further study of the biology of D. dipsaci, as well as determining which method of cleaning seed is most effective, to reduce the spread.Part of the grant money will also go towards subsidizing the cost of testing grower’s garlic and soil samples for nematode infection.While young nematodes typically target the bulb, stem, and leaves, mature nematodes may move into the soil, potentially infecting other crops and contaminating the soil for many seasons to come.To address this problem, Crystal Stewart, in association with the Cornell District Vegetable and Small Fruit Program, has been studying the ability of D. dipsaci to overwinter in the soil. For the past two years, samples were collected in the spring from fields where the nematode had been confirmed present. Results from both years suggested that D. dipsaci was not able to survive.These results, however, may have been offset by the fact that both springs saw heavy rainfall, which could have drowned nematodes that may have otherwise survived.According to Abawi, the best thing that growers can do to keep D. dipsaci at bay is to plant clean seed that has been tested for nematodes into non-infected soil that has been rotated with crops outside of the allium family for at least four years (the allium family also includes popular crops such as scallions, chives, and leeks).“In the past five to ten years, garlic has just boomed. People love garlic, and they love to grow garlic,” Ivy said. She continued, “Everyone grows tomatoes –– garlic is bit of a newer crop. Garlic used to come with few problems, but now has been around long enough that the problems have found it.”

Original Author: Paige Roosa