Improved brown rot test helps ID fungicide resistance in stone fruit

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

A quick test for fungicide-resistant brown rot disease in peaches also may aid strawberry growers struggling with similar fungal diseases.

Guido Schnabel, associate professor of fruit pathology at South Carolina’s Clemson University, says the same technique used in the brown rot test should translate into a system for anthracnose and botrytis fruit rots in strawberries.

An $850,000 U.S. Agriculture Department grant will fund his strawberry work, which includes developing a resistance monitoring tool and implementing a spray application decision support system.

The grant is part of a larger multi-university project to improve management of both diseases.

For brown rot, fungal samples collected in the field with special test kits show within 72 hours any sensitivities to specific fungicide classes.

Used for the past three years in Southeastern peach orchards, the test should work equally well for any pathogen that sporulates, grows on artificial medium and develops early in the season, Schnabel says.

Among them would be gray mold of grapes and brown rot infections in cherries and other stone fruit, he says.

The technique works best with fungi whose spores are easily collected and easily grown in a Petri dish.

Unfortunately, that rules out a similar test for downy and powdery mildews, says Phil Brannen, associate professor of plant pathology at the University of Georgia in Athens.

A more user-friendly test

Schnabel and Brannen worked together to develop and improve the brown rot test, making it more user-friendly.

A new online application—viewable at http://bit.ly/gx6qhN—delivers test results with spray recommendations tailored to individual resistance situations.

Their work has helped growers fine-tune their spray programs with a more accurate sense of risk versus cost, Brannen says.

That’s given growers more confidence and fewer worries about brown rot, says Lawton Pearson, a partner in Pearson Farm in Fort Valley, Ga.

“The biggest pathogen and fight for us is brown rot,” Pearson says.

Some years are worse than others, with more favorable conditions to the disease. Six years ago a severe outbreak of fungicide-resistant brown rot—developed through continued reliance on sprays from a single chemistry class—hit home with the need to rotate modes of action, he says.

“In one block, half the peaches had to be put on the ground,” he says.

The tests not only ended the uncertainty about which blocks held resistant brown rot, but also helped target the orchard’s fungicide use.


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