Smudge, or anthracnose is caused by Colletotrichum circinans (Berk.) Voglino which primarily affects white onions at harvest and during storage. Small dark green or black spots appear around the neck and on outer scales, often in concentric rings. These spots may spread on inner scales and form small yellow lesions. The fungus can survive on onion debris and in soil for several years. Infection is favored by warm (80° F) moist weather, especially near harvest.
Disease management recommendations include crop rotation out of onions for three years; use clean seed and non-infected transplants; good drainage; timely applications of fungicides such as mancozeb (Manzate), chlorothalonil (Bravo), and iprodione (Rovral); let onions dry out completely at harvest and/or heat treat before storing; store dry onions at 32° F and less than 70 percent relative humidity.
Categories: Onion, Diseases, Fungal diseases, Smudge
Date: 04/01/2007