Faster response to fight peach brown rot on the way

Published: September 2, 2010

CLEMSON — Choosing weapons to fight fungicide-resistant brown rot is about to get easier, thanks to Clemson University research. Funded by a USDA Southern Regional Integrated Pest Management grant, the new project will put treatment advice online, giving specialists the ability to give growers immediate fungicide recommendations after testing for brown rot resistance.

The “profile” kit has saved Georgia and South Carolina peach growers $20 million in wasted fungicides and prevented yield loss due to resistant brown rot (Monilinia fructicola) since its first use three years ago. Scientists at Clemson University and the University of Georgia developed the kit after extension specialists began reporting fungicide failure in peach orchards infected with M. fructicola. The kit enables specialists to monitor for resistance to five chemical classes of fungicides.

In the southern peach-growing states, only three fungicide classes have been effective against brown rot: benzimidazole (BZI), demethylation inhibitor (DMI) and respiration inhibitor (RI) fungicides. Strains of M. fructicola have shown resistance to each of the fungicide classes. Currently, there are pockets of resistance to one of the fungicide classes throughout the South Carolina and Georgia production areas, but so far no fungus has been detected with resistance to more than one.

Extension agents and specialists have been using the kit to inform peach growers which fungicides to use on peaches stricken with resistant M. fructicola. In an earlier version of the kit, specialists cut pieces of fungicide-filled agar from a lip balm tube and placed them in a culture dish with swirls of spores from infected fruit. More recently the scientists switched to an even quicker assay that involves a 24-well plate pre-filled with fungicide amended agar. The specialist lets the cultures sit for three days and then checks the spore growth. If the spores grow on the fungicide-amended medium, the specimen is resistant to that fungicide.

Extension agents record the data, communicate them to the state specialist, who analyzes the data and writes a resistance-management recommendation for the grower. The process can take several days.

The future online component will speed up the time between the observed results in the dish and the recommendation, saving fungicide sprays that may be unnecessary or ineffective.

“With the new web application, we basically accelerate the time from data collection to providing resistance-management recommendations,” said Guido Schnabel, Clemson University plant pathologist and one of the project directors. “The data is entered into the web application, and data analysis, as well as recommendations, are provided real time. This information can be sent immediately by e-mail to the grower whose sample was analyzed.”

Schnabel said the online system will allow growers to react more quickly to potential resistance problems. The USDA grant to Clemson is $54,040.

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