Bacterial leaf scorch, caused by the bacterium Xyella fastidiosa, causes what looks like burns on the blueberry leaves. The scorching occurs when the bacteria invades the xylem of the plant, preventing the plant from transferring nutrients and water.

“The plumbing of the plant is basically clogged,” he said. “The plant shows symptoms of drought stress and eventually dies.”

Some growers have cut back infected plants and managed to get another year of production, but Brannen said the infected plants eventually die.

In the field, the southern highbush cultivar Emerald appears to be fully resistant to this disease. Brannen said the varieties Winsor and Millennium can tolerate the disease, but are not completely resistant.

The most susceptible varieties are V1, O’Neal and Star. Unfortunately, timing and quality have traditionally made these varieties top picks for growers. In many locations, these varieties are being replanted to other varieties — a major expense, he said.

“If a grower has invested in V1 plants, they will have 100 percent loss in 10 years if they are infected with Xyella, losing 10 to 20 percent each year,” he said. “Growers invested in Star will see a 30 to 40 percent reduction in plants in 10 years.”

Without disease, highbush varieties could produce for 10-15 years or longer.

Right now, there are no chemicals confirmed to control these diseases, he said. But if it is determined that insects are the vectors that spread the diseases, as is the case with Xylella and possibly necrotic ring blotch, some insecticides may help.

Brannen said breeding new varieties with resistance to the diseases is the best answer.

“Breeding may have allowed the diseases to surface, so we could have inadvertently released varieties susceptible to these diseases, while our natives are resistant,” he said. “The berries may have great market characteristics, but we may realize later that they are susceptible to disease.”

Brannen is working with University of Florida scientists to develop screening programs. Field screening could take five to six years, but greenhouse screening, if possible, would be faster, he said.

“We are hopeful for a greenhouse screening program, but initial results suggest we need to screen in the field,” he said. “These diseases have been confusing and difficult to deal with.”