Improved brown rot test helps ID fungicide resistance in stone fruit - The Packer

Improved brown rot test helps ID fungicide resistance in stone fruit

05/01/2011 09:52:00 AM
By Renee Stern, Contributing Editor

“We may not be spending less money, but we get 100 percent control,” Pearson says. “We have enough bullets [in the spray program] if we know when and how to use them.”

Resistance-management strategies

Standard protocols to control brown rot are too general, given microclimates that create different disease conditions across even a small region, Schnabel says.

And individual spray patterns in previous years can foster different resistant fungi populations from farm to farm.

“Growers want location-specific information,” he says.

Ideally, widespread use of the resistance test will reduce the need for fungicide sprays through more targeted use, he says.

“It’s a tool to develop a long-term resistance strategy,” says Greg Henderson, a Clemson Extension agent for commercial fruit in Edgefield, S.C. With it, growers can correct missteps in fungicide programs before they become critical mistakes.

Resistance will persist in blocks once it gets a toehold, requiring a complete management change for affected areas, he says.

Results over the past two years hint that resistance to one class of brown rot fungicides—demethylation inhibitors such as propiconazole and metconazole—may be diminishing, Brannen says. That’s a difficult conclusion to validate, however.

At the same time, a trend toward strobilurin resistance is surfacing in southern Georgia orchards, he says. The test kits allow close monitoring to stave off serious problems there.

That monitoring capability also allows growers to check their orchards throughout the growing season.

Should any resistance issues pop up, they can amend their spray programs immediately, he says.

How many samples?

One question still to be resolved is how many samples are needed to provide an accurate snapshot of an orchard’s brown rot population, Brannen says. Current recommendations call for sampling 10 peaches.

“There is potential for false negatives,” where sampling might miss hot spots with resistant fungi, he says. Take samples in multiple spots rather than from a single tree.

The tests also may report false positives, most likely due to contamination when collecting samples.

“The results are only as good as the samples you take,” Henderson says. “It takes a lot to mess up, but you can mess it up.” Although careful handling to keep the swab and sample tube clean is critical, “You can train anyone to use this kit in an hour,” he says.

The researchers plan another year of screening and improving the test before releasing a final version to Extension agents and growers for their use, Brannen says.

“I’d like to see [the test] in a form that I could do it myself,” Pearson says. His experiences so far have sold him on its value.

“There’s a lot to be said for sleeping at night when you feel confident your peaches are protected,” he says.

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