HPIPM:Onion Storage Mold

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Eurotiomycetes
Subclass	Eurotiomycetidae
Order	Eurotiales
Family	Trichocomaceae

Scientific Name

Penicillium

Common Name

Penicillium fungi

Author: Howard F. Schwartz, David H. Gent, and Mike Bartolo

Identification and Life Cycle

Black mold is caused by the fungus Aspergillus niger, and can be a problem wherever onion is grown. The fungus can grow saprophytically on dead plant and animal tissues, and is a common soil inhabitant. The fungus can also grow within all onion tissues as an endophyte, but only causes symptoms on plants when environmental conditions are favorable. Infection occurs when spores land on and colonize leaves through wounds or natural openings, through wounds or cut necks at harvest, or endophytically by contaminated seed. The pathogen can survive between onion crops as a saprophyte on decaying organic matter, in onion seed, and on cull onions.

Blue mold is caused by several species of the fungus Penicillium, and is principally a pathogen only on stored bulbs. Like A. niger, the fungus can grow saprophytically on dead plant and animal tissues, and is a common soil inhabitant. The pathogen can survive between onion crops as a saprophyte on decaying organic matter, in or on onion seed, and on cull onions.

Plant Response and Damage

Black mold symptoms generally begin at the top of the bulb near cut necks and progress downward. Infected tissues initially become water-soaked, but later a black mold is apparent between scales; small black sclerotia later form. This tissue will dry and shrivel, but can become soft and watery if invaded by bacteria. Bulbs can appear healthy on the outside, but have at least one diseased inner scale when cut in cross-section. Losses can be significant if high temperature curing is not monitored closely.

Blue mold symptoms include a soft, watery rot with a blue-green mold apparent on the surface.

Biological Control

Biological control strategies have not been developed for black and blue mold.

Cultural Control

Plant high quality onion seed free from the storage mold pathogens. Practice crop rotations of at least three years between onion crops. Thoroughly cure bulbs in the field and storage shed with ambient air, but avoid bruising and wounding during harvest. High temperature curing can favor black mold, so bulbs must be closely monitored to prevent infection of bulbs during forced air curing.

Chemical Control

Seed treatments and timely applications of fungicides, especially those with some systemic activity, may reduce storage mold losses.

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.