Sour skin

Sour skin (Burkholderia cepacia) primarily affects onion bulbs, but foliar symptoms may also be observed from time to time. This disease usually manifests itself during harvest when temperatures above 29°C (85°F) are uncommon. Burkholderia cepacia was discovered by Walter Burkholder in 1949 and was first described as a human pathogenic bacteria in the 1950s. In the 1980s, it was first recognized in individuals with cystic fibrosis, and outbreaks were associated with a 35% death rate.

Symptoms
Foliar symptoms, when observed, are similar to those of center rot. Scales of infected bulbs develop a cheesy or slimy yellow growth and brown decay. Infected scales may separate from adjacent scales allowing firmer inner scales to slide out when the bulb is squeezed. Sour skin infected bulbs usually have an acrid, sour, vinegar-like odor due to secondary organisms.

Prevention
Avoid overhead irrigation near harvest time to reduce losses to this disease. Also use practices that reduce the chance of irrigation water becoming contaminated with the sour skin bacteria. Avoid damaging onion foliage prior to harvest as this provides wounds for the bacteria to enter bulbs. The mature bulbs should be dried as soon as possible after harvest to reduce post harvest losses. Discard infected bulbs before storing, as disease can spread from infected bulbs to healthy bulbs. Store onions in cool, 0°C (32°F), dry areas to prevent bulb-to-bulb spread of sour skin.