Fruit rot of mature dried plum fruit caused by the brown rot fungus.

Fruit rot of mature dried plum fruit caused by the brown rot fungus.

A new, interactive Web site developed by the University of California to help dried plum growers make brown rot management decisions may serve as a model for other stone fruits. Brown rot, caused by Monilinia fructicola and M. laxa, is the number-one disease problem for stone fruits in California, said Dr. Themis Michailides, plant pathologist at UC’s Kearney Agricultural Center in Parlier. Field losses can be extensive and can ruin half or more of the fruit before harvest, with the remaining fruit subject to postharvest infection.

Michailides used the crop loss of a northern California prune grower, who didn’t check for brown rot infection later in the season last year, as an illustration of the disease’s damaging nature. “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.”

But plum growers now have help in making disease management and control decisions with a new Web site designed to address brown rot in dried plums. Growers can access information to help them make better spray decisions and reduce unnecessary fungicide use. The project was funded by a three-year UC integrated pest management program grant and support from the California Dried Plum Board.

The Web site is similar to crop models that have been developed for other diseases like powdery mildew for grapes and fireblight for apples and pears, in that it helps growers assess the potential for disease incidence and make science-based spray decisions instead of spray decisions based on the calendar.

“As far as I know, this is the first one developed in the United States for brown rot,” he said.

Michailides’s goal is to expand the Web site to other stone fruits. “With the help of our IPM grant, we also developed similar information for other stone fruit produce like peaches and nectarines,” he said.

“We do need to do additional work on brown rot for the other stone fruits.”

Brown rot

Michailides noted that the first indication of brown rot in the spring is the rapid death of blossoms. As the blossoms turn brown, they often become affixed to the twig in a gummy mass. Infected blossoms later become covered with a grayish to tan spore mass. Young fruit is not usually susceptible to the disease unless it is damaged or punctured to give spores internal access. Soft, mature fruit are more easily infected, and under optimum conditions, can be rotted within 48 hours.

Researchers have developed an easy-to-use technique for fruit growers to determine if there are latent infections so they can tell if they need to spray fungicides preharvest and how many treatments are necessary to prevent brown rot.

Once a grower registers on the Web site, he or she answers a few simple questions based on the disease history of the orchard, developmental stage of the crop, and the weather forecast that is provided through the site by a link. To run the system, the grower then chooses the appropriate time period, which begins in March and runs through the end of August.

The program then provides stage-dependent decision information for brown rot management. By monitoring the temperatures and moisture levels in the orchards, the program can help users determine timing of fungicide application, irrigation, fruit thinning, and other management practices helpful in controlling disease.

Three different statements are given by the system: Note, Warning, and Recommendation. In the note statement, information about the current situation and disease development is given, including susceptibility of bloom or fruit. The warning statement tells users about possible risk of disease development, risky weather, and estimation of future disease severity. The recommendations relate to disease management, integrated pest management strategies, and timing of spray and horticultural practices.

Visit the site at: TJM-Site/brown-rot-homepage.htm.