IPM grants help peach and strawberry growers thwart resistant crop diseases

In 2006 an Extension plant pathologist from Clemson won a $115,000 Regional IPM grant from USDA National Institute of Food and Agriculture (then CSREES) to develop a kit that would help peach growers in Georgia and South Carolina choose an effective fungicide to fight resistant brown rot disease. That initial investment spurred at least three additional grants that refined the kit and has since benefited both the peach and strawberry industries at an estimate of $12 million.

In 2002 southeastern peach growers discovered something they hoped they would never find—a strain of brown rot disease they could not kill. During years of heavy rains and high humidity, brown rot (Monilinia fructicola) can reduce yields by about 20% if left untreated. Growers have only three options for fungicides to treat brown rot; however, scientists have discovered strains of brown rot that have shown resistance to one of each of the three fungicide classes. In 2008, resistant M. fructicola disease cost growers $9.8 million in losses.

A $69 million industry based primarily in South Carolina and Georgia, peach production is vital to the economy of both states. So Clemson University researcher Guido Schnabel and University of Georgia researcher Philip Brannen teamed up on three consecutive projects to manage brown rot disease, funded by the Southern Regional IPM grant program (S-RIPM).

With the first two projects, Schnabel and Brannen developed an assay to test spores from infected fruit, held in a lipbalm tube. At the time, M. fructicola was resistant to two of the three fungicides. However, cutting agar from the tube to transfer to a Petrie dish proved cumbersome, so with the third project, which also included a web-based reporting and recommendation system, the handheld kit was a 24-well plate, pre-filled with fungicide amended agar. The multi-well plate was necessary after researchers discovered strains of M. fructicola that were resistant to the third fungicide.

The online recommendation system prescribes which two fungicides will be effective at treating the disease. Growers in both states are using the system and following the recommendations.

“It has also been a good educational experience for the growers,” says Schnabel. “Growers said they’ve learned about the chemical classes of fungicides and how to make them work to manage disease. All of this happened because of that first S-RIPM grant [in 2006].”

Schnabel says that incidences of brown rot disease has been minimal in the last few years because growers now know how to manage the fungicide resistance.

The model was so effective that he was encouraged to use a similar model for a different fruit crop. In 2014, Schnabel received a SIPMC IPM Enhancement grant to use the model to determine resistant Botrytis (gray mold) in strawberry. The resistance monitoring for strawberry growers is location-specific; recommendations are based on several factors, including where the grower obtains plants, what other crops are in the area, and the spray history. Schnabel says growers are adjusting their spray programs because of the recommendations and are using the system.

“Strawberry growers have saved about 10% of their yield because of the program,” says Schnabel. “That yield would have been wasted if they were using the wrong fungicide. They are also not spraying anything that doesn’t work, so they aren’t wasting material and then having to switch to something else.”

The Southern Region Small Fruit Consortium has been a valuable partner to both researcher and grower: the Consortium pays the assay fee for the growers, saving growers over $100 to have their disease samples tested. Schnabel says that the money encourages more growers to be involved, helping him to track problem areas.

The benefits to peach and strawberry growers from these four projects are estimated to total $12 million in 2014. Investment by USDA NIFA and the Southern IPM Center for the four grants totaled $356,678, a $33.6 return for every grant dollar.

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