HPIPM:Onion Slippery and Sour Skin

Taxonomy

Domain	Bacteria
Phylum	Proteobacteria
Class	Betaproteobacteria
Order	Burkholderiales
Family	Burkholderiaceae
Genus	Burkholderia

Scientific Name

Burkholderia cepacia

Scientific Name Synonyms

Pseudomonas cepacia

Common Name

sour skin of onion

Author: Howard F. Schwartz and David H. Gent'

Identification and Life Cycle

Slippery and sour skin are caused by two different but related bacteria, Burkholderia (formerly Pseudomonas) gladioli subsp. alliicola and B. cepacia, respectively. These bacteria are very common soil inhabiting organisms, and are probably found in many or most High Plains soils. Infection occurs when contaminated soil or water splashes onto leaves, and the bacteria enter through wounds or natural openings and progress downward into bulbs. Infection also may occur through wounds when tops fall over or through cut necks at harvest. The slippery and sour skin pathogens survive between onion crops in soil.

Plant Response and Damage

Foliar symptoms of slippery and sour skin include a canker phase in which the bacteria generally cause a necrotic bleaching and collapse of one or two leaves. The pathogens progress down the leaf into the bulb, where they cause a pale yellow to light brown decay or breakdown. Slippery skin generally progresses downward in one scale until it reaches the basal plate, whereupon it spreads to other scales. The entire center scales of the bulb can become rotted and watery, and slip out when pressure is applied to base of the bulb. Sour skin generally appears as a decay of one or a few outer scales, but adjacent outer and center scales may remain firm. A foul, acrid smell is present. The center portion of the bulb slides out when pressure is applied, but is not decayed. Yield losses of 5 to 50% have been reported.

Biological Control

Incorporation of green manure crops the season before onions are grown can reduce B. cepacia populations in soils. No biological control strategies have been developed for slippery skin.

Cultural Control

Practice a three to four year crop rotation with small grains or sugarbeet. Avoid rotation with corn. Avoid reuse of irrigation water and overhead irrigation, especially after bulb initiation. Provide adequate but not excessive nitrogen fertilization, especially after bulb initiation or storm damage. Promptly harvest after bulbs have thoroughly cured in the field. Avoid wounding or bruising bulbs during harvest and storing operations. Promote rapid drying with forced air curing before long-term storage at 32 to 36ºF with a relative humidity of 70% or less.

Chemical Control

Copper bactericides provide some disease control in Colorado when applied before disease is observed. Sprays should be initiated two weeks before bulb initiation, and continued on a 5 to 10 day spray interval depending on weather conditions. Apply in a sufficient volume of water to ensure thorough coverage. Include a low rate of a non-ionic surfactant to further improve coverage.

Copper tolerant strains of the pathogens are common in the U.S. Tank mixing copper bactericides with a low rate of an EBDC fungicide such as maneb is essential for effective disease suppression. Tank-mixing coppers with zinc or iron can also enhance their activity.

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.