In California, prune orchards are concentrated in Sacramento, Santa Clara, Sonoma, Napa and San Joaquin Valley. Currently, these acres produce more than twice as many dried plums as the rest of the world combined: approximately 99 percent of the U.S. supply, according to the California Department of Food and Agriculture.

Plant pathologist Themis Michailides and project scientist Yong Luo from the Kearney Agricultural Center in Parlier initially developed a Web site to address brown rot in dried plums. Funded by a three-year UC Statewide Integrated Pest Management Program grant and a grant from the California Dried Plum Board, Michailides improved the site by adding interactive, science-based information to help growers make brown rot control decisions not only during bloom time, but also later in the season.

Growers answer a few simple questions, based on the history of the orchard, the developmental stage of the crop, and the weather forecast (through a link in the site). The program determines the best spraying times by monitoring the temperatures and moisture levels in orchards. It can also help users to determine the timings of fungicide application, irrigation, and fruit thinning for disease control.

“Brown rot is highly destructive and can ruin half or more of the fruit before harvest, with the remaining fruit subject to postharvest infection,” says Michailides. “Last year a grower in Butte County didn’t check for brown rot infection later in the season. He lost about 40 percent of his crop at harvest due to brown rot.  When you consider the added cost of spraying and the reduction of salable fruit due to disease, that’s a big loss.”

The first indication of brown rot in the spring is the rapid death of blossoms, which, as they turn brown, often become affixed to the twig in a gummy mass. They later become covered with a grayish to tan spore mass. Young fruit is not usually susceptible to brown rot unless it is damaged in some way, giving the spores access to the interior of the fruit. Once the fruit ripens and becomes soft, it is more easily infected.

"With good production practices, good pruning, good spray programs, and good site selection, those things can be minimized," says Michailides.  “One important improvement is that we determined the significance of latent infection later in the season and determined the right time to check for it in a prune orchard. The incidence of latent infection in prunes indicates to growers whether they need to spray fungicides at preharvest and how many treatments are necessary to prevent brown rot.

“With the help of our IPM grant, we also developed similar information for other stone fruit like peaches and nectarines,” he says. “Our goal is to expand the decision support system for other stone fruits.”

Visit the site at http://tjm.uckac.edu/TJM-Site/brown-rot-homepage.htm

For more information on brown rot, look under prunes on the UC IPM Web site at http://www.ipm.ucdavis.edu/PMG.

Media Contacts:

Stephanie Klunk, Communications Specialist

UC Statewide IPM Program

(530) 754-6724

sjklunk@ucdavis.edu

Themis Michailides, Plant Pathologist

Kearney Agricultural Center, Parlier

Office: 559-646-6546   Lab: 559-646-6562

themis@uckac.edu