The stem or bulb nematode, Ditylenchus dipsaci (Kuhn) Filipjev, can attack over 400 plant species including alfalfa, onion, bean, soybean, potato and many common weeds. It has been a minor problem on onions in western regions. Infected seedlings become dwarfed, twisted and abnormally white with swollen split areas. Plant stands may be erratic. In older onion bulbs, tissue softens near the top of the bulb and at the base of leaves of stunted plants. Older plants often crack or produce doubles. Secondary breakdown by bacteria and fungi is common. Nematodes survive on seeds, onion debris, weeds and in infected transplants. The pathogen is favored by free moisture and an optimum soil temperature of 70° F. Its life cycle is completed within 23 days at 15° C with four molts and four juvenile stages; and adults live up to 73 days. Damage occurs in many crops at infestation levels as low as 10 nematodes per 500 grams of soil.
Disease management recommendations include crop rotation out of onion and other hosts for four or more years; debris sanitation and weed control; nematode-free seed and transplants; absence of infested soil or contaminated equipment; reduction of stresses such as soil compaction and poor water drainage; and fall fumigation with dicloropropene (Telone C-17).
Categories: Onion, Diseases, Nematode, Stem Bloat, Bulb Bloat
Date: 04/01/2007