Effect of Irrigation Management on Sour Skin of Onion. Beth L. Teviotdale, Kearney Agricultural Center, University of California, Parlier 93648. R. Michael Davis, John P. Guerard, and Dennis H. Harper. Department of Plant Pathology, University of California, Davis 95616; University of California, Cooperative Extension, Bakersfield 93303; and Kearney Agricultural Center, University of California, Parlier 93648. Plant Dis. 73:819-822. Accepted for publication 24 April 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0819.

The incidence of sour skin of onion, caused by Pseudomonas cepacia, was greater in plots irrigated by overhead sprinklers than in plots irrigated by furrow the entire season or irrigated by sprinklers until bulbing and then by furrow. In three trials that varied the rate of water delivered by sprinklers (2.5–6.7 mm of water per hour, which is about the range used in commercial fields), there was no correlation between millimeters of water applied and incidence of disease. In an experiment using extreme differences in sprinkler irrigation (0.6–9.3 mm of water per hour), however, the number of infected onions was positively correlated with millimeters of water applied. There was no significant difference in number of rotted onions between two planting densities (52 and 79 plants per meter). Onions inoculated at weekly intervals from 3 wk before bulb formation to 1 wk after bulbing developed external disease symptoms at the same time, about 3 wk after bulbing.