Rainy, cool spring may create 'perfect storm' for strawberries, Clemson researcher says
January 10, 2012
CLEMSON, SC – January 9, 2012 – A Clemson University plant disease researcher has disturbing news forSoutheastern strawberry growers. Research data show that the funguscausing gray mold in strawberries has become completely resistant tosome important pesticides that producers have been relying on for years.
“If the wrong products are used during weather conditions suitablefor gray mold disease we will experience the ‘perfect storm,’” saidGuido Schnabel, research and Extension plant pathologist at ClemsonUniversity. Gray mold is a serious disease affecting the plant and fruitof the multibillion-dollar crop.
“I will have to let growers know that some products we have beenusing are no longer effective and resistance to other products isalready emerging,” said Schnabel, who presented his research Saturday atthe Southeast Regional Fruit and Vegetable Conference in Savannah.
“There are several chemical classes available to control Botrytisblight, crown rot and gray mold disease. The ones that have been usedfrequently are now quickly selecting for resistance in the pathogen,”said Schnabel.
Gray mold is one of the most common and serious diseases whereverstrawberries are grown. The fungus, Botrytis cinerea, causes crown rot,tissue blight and fruit rot. During wet seasons on unsprayed plants,losses of up to 90 percent of flowers and fruit can occur.
Schnabel believes growers are unaware of the problem because controlfailure has not yet occurred. Recently, there have been a lot of yearsof dry weather that would not support a widespread outbreak of thepathogen. Still, growers applied fungicides unknowingly selecting forresistance.
“Growers may think they are controlling the disease with weeklysprays, but in reality it is the relatively dry weather that preventedthe pathogen from taking off,” he said. “Resistance has built up to suchlevels that the use of some chemicals is no longer justifiable. It’sjust going to take one wet year and the wrong chemicals and we are goingto have a big problem. I really am glad we caught this early to be ableto counteract.”
But Schnabel also says that growers still have sufficient options foreffective disease control. “The good news is that a sufficient numberof chemical classes that — if rotated correctly — should allow forreliable disease control,” he said.
The goal for Schnabel, who is part of a regional strawberry researchproject headed by University of Florida, is to make growers aware of theproblem and to get them on board for a regional resistance-monitoringprogram.
“We are in the process of offering to growers in South Carolina,Georgia, North Carolina and Florida a service that will give them theinformation they need to make science-based decision about spraying andkeeping it effective.”
Schnabel’s research group collected samples taken from four countiesin North Carolina and from eight counties in South Carolina.
“We found resistance to certain chemical classes in all of thesampled areas,” he said. “Resistance is based on point mutations in thefungicide target genes, which really is the worst possible kind ofresistance. That means even an increase of the dose will not matter.”
Schnabel received $850,000 from the four-year, $2.9 million USDA National Institute of Food and Agriculture grant that supports efforts to forecast outbreaks of two fungal diseases threatening the nation’s $2.1 billion strawberry crop.
Managing emerging fungicide resistance in strawberries is just oneaspect of the proposed research. With the help of a disease forecastsystem to predict high risk of infection by analyzing air temperatureand leaf wetness, the number of total applications can be drasticallyreduced, said University of Florida plant pathologist Natália Peres, theregional project leader. Experiments so far have shown that growers canpotentially reduce fungicide use by half without compromising diseasecontrol.
The grant will enable the team to test the system in otherstrawberry-producing states, including South Carolina, with the addedcomponent of monitoring fungicide resistance and advise growers ofalternative fungicide options.
