Diseases Of Onions

Donald M. Ferrin, Hadziabdic, Denita, Hollier, Clayton A., Overstreet, Charles

Onion brown stain is caused by Botrytis cinerea. The pathogen causes tan stains on the outer scales of storage onions by either penetrating the scale directly or by growing down into the scale from the leaf sheath or the leaf itself.

Fusarium basal rot is caused by the soilborne fungus, Fusarium oxysporum f. sp. cepae. The pathogen can affect onion bulbs at any stage of development. Initial symptoms include rotting of the roots, with white-to-pinkish mold developing at the base of the bulb. Infected plants may wilt and, in severe cases, die.

Downy mildew is caused by Peronospora destructor. Disease is favored by warm, wet weather. The first symptom of disease development is purple-gray velvety growth on the leaves. Infected leaves soon turn yellow, collapse and die.

Onion smudge (anthracnose) is caused by the soilborne fungus Colletotrichum circinans. Smudge occurs mainly on the dried outer scales and lower portions of white onion, causing black, target-spots. Good sanitation practices, crop rotation and adequate drainage may help prevent disease outbreaks.

Pink root is caused by the soilborne pathogen, Phoma terrestris. Initially, infected roots are light pink, becoming darker as the disease progresses. Plants are stunted, with leaf numbers often reduced. Smaller bulb size is usually the main effect of this disease.

Neck rot is caused by Botrytis allii. The pathogen infects plants during the harvest, causing significant damage on stored bulbs. Allowing plants to mature fully (neck area of the onion becomes smaller and drier) before harvesting can prevent disease outbreaks.

Onion white rot is caused by Sclerotium cepivorum. It is one of the most important and destructive fungal diseases of the Allium family. Early symptoms include premature yellowing, wilting and death of older leaves. Rotting of the roots is characterized by the presence of white, fluffy mycelial growth that develops around the base of the bulb. As disease progresses, sclerotia (small black round bodies) are formed.

12/7/2005 2:42:08 AM
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