Death of seedlings before and after emergence can be caused by various species of Pythium and Fusarium. Older reports also claim that Rhizoctonia can be involved. Plants are often infected at the soil line or slightly below; tissue turns tan to brown, watersoaked, and shrinks rapidly while aboveground parts wilt and fall over. Root systems of seedlings and transplants are rotted by these fungi or damaged by nematodes. Therefore, roots are killed directly or weakened and predisposed to additional damage by other stress factors such as cold, wet soil, compaction, herbicides, and salts from alkaline soil or fertilizer.
Disease management recommendations include crop rotation out of onions for three years; plant seed treated with a fungicide such as Thiram and/or metalaxyl (Ridomil); good seedbed preparation that promotes adequate drainage and rapid emergence; and reduction of other stresses such as cold soil, soil compaction and poor drainage, or improper fertilizer placement. A seven to ten inch banded fungicide such as Ridomil applied at planting provided an average increase in plant stand of 13 percent (range from five to 22 percent) in commercial fields of seeded onions.
Categories: Onion, Disease, Fungal Diseases, Damping-Off, Seedling Blight
Date: 02/26/2002