Stem and Bloat Nematode of Onion and Garlic: A Re-Emerging Pest of Garlic and Onion
Posted: May 1, 2013
Dr. George Abawi, Cornell University spoke recently at the Mid Atlantic Fruit and Vegetable Convention about stem and bloat nematode. This pest has been in the United States since the 1930s. Recently, in 2010, severe damage to garlic was reported in a New York garlic field. In response Cornell Extension and the Garlic Seed Foundation surveyed garlic fields across New York State and found that the problem is widespread, affecting 30% of fields in at least 17 counties. To date bloat nematode has been confirmed in Canada, Vermont, Massachusetts, Pennsylvania, and several other states.
Symptoms and Damage
Severely infected garlic plants grown from infected seeds exhibit stunting, yellowing and collapse of leaves, and premature defoliation. The bulbs of infected plants initially show light discoloration, but later the entire bulb or individual cloves become dark brown in color, shrunken, soft, light in weight and eventually exhibit cracks and various decay symptoms due to the additional activities of numerous saprophytic soil organisms. However it can be very difficult to distinguish nematode infected bulbs from other problems. If you suspect that you have a problem Pennsylvania growers can send a sample to the Penn State Plant Disease clinic.
Soil nematodes are microscopic round worms. Some of these round worms feed on plants, others feed on bacteria, fungi or other microscopic organisms. The bloat nematode, a plant feeder, lives some of its life cycle in the soil. For much of its life it lives and feeds inside leaves, stems, and bulbs of onion and garlic. Because it has a special stage of its life cycle where it can withstand very dry conditions it can survive for several years in infected plant tissue or soil. The nematode can only move small distances through the soil on its own. But it is easily spread through infected seeds and plant material, irrigation water or surface run off, contaminated equipment or other soil movement.
What can you do to prevent and manage bloat nematode?
- Plant Only Nematode-Free Seeds.- Infected planting materials is the major source for introducing this important pathogen into new production areas, thus it is critical to use only clean seeds to prevent the establishment and damage of this nematode.
- Hot Water Treatment of Planting Materials.- Considerable information is available in the literature on various hot water treatment protocols against the bloat nematode in garlic bulbs and plant materials of other crops. Depending on the soaking time, water temperature reported to reduce the population of this nematode have ranged from 38 – 49 C (100 - 120 F). However, water temperature above 50 C (122 F) appears to injure garlic tissues. Also, dipping garlic bulbs in hot water alone without other additives (sodium hypochlorite, avermectin, formaldehyde, various fungicides, or other chemicals) were not as effective. It appears that the most used protocol is dipping for 20 minutes at 49 C (120 F). Hot water treatment should be considered only when clean bulb are not available, as even the best hot water treatment does not completely eliminate the nematode and may also increase other disease problems.
- Avoid infested Sites or Treat the Soil with an Appropriate Control Product.- Nematode-free seeds should be planted in soil free of infestation with the bloat nematode. If there is any question, the soil of the target site should be sampled and analyzed for the presence of the bloat nematode. Garlic grown for seeds should be planted in nematode-free soil. In addition, a population of as low as 10 bloat nematodes/500 cc soil has been reported to cause damage in many crops. Pre-plant soil fumigation with registered nematicides will control this nematode as well as other plant-parasitic nematodes, where needed and if cost-effective. Mixed results have been reported in the literature with the use of non-fumigant-type nematicides in controlling the bloat nematode and only limited evaluations have been conducted to-date in New York.170
For more detailed information see Dr. George Abawi’s report in the Mid Atlantic Fruit and Vegetable Convention Proceedings 2013.