Peach growers are currently in need of ways to control bacterial spot, a severe disease that is at its worst when rain is frequent. Dave Ritchie, a plant pathologist at North Carolina State University, spoke about the disease and management options for growers at the 2019 Southeast Regional Fruit and Vegetable Conference.
Bacterial spot is particularly challenging because of the lack of controls growers and researchers have for the disease. “In years where it occurs, depending on the weather, it can actually cause almost a 100 percent loss on some of the highly susceptible varieties,” Ritchie said.
The only real option growers have right now is to plant varieties less susceptible to the disease, says Ritchie. He explains that most of the highly susceptible varieties grown in the Southeast are developed on the West Coast, where bacterial spot isn’t a problem for growers. These varieties are then planted into an environment that is extremely conducive for bacterial spot. Hot, wet, humid summers that occur every year in the Southeast allow the disease to thrive.
There are limited cultivars available in the Southeast that are resistant to the disease. These cultivars vary according to what region the grower is in. Some are highly resistant but not very marketable.
Ritchie says practicing good pruning, which will allow for better spray coverage of copper products or antibiotics, is one cultural control growers can use. He hasn’t found any biological controls yet that are cost effective, and he says there are no insecticides to help growers combat bacterial spot.
Ritchie recommends growers who are dealing with bacterial spot on a year-to-year basis should use pre-bloom copper sprays “from about bud swell through shuck split … to try to reduce the amount of bacteria that will build up.” He considers pre-bloom sprays essential, rather than waiting to shuck split. Ritchie says that in the time period from bud swell to bloom, the bacteria can build up to a very high level but symptoms may not be visible.
According to Richie, there are years when peach growers are unable to control bacterial spot. When growers experience high precipitation rates, it makes it nearly impossible to control. Ritchie says more research is needed to develop varieties with bacterial spot resistance. “My feeling is genetics is going to be the answer,” he concludes.