By Sharon Omahen
University of Georgia
In addition to the extensive crop damage from this fall's hurricanes, a handful of Georgia pecan growers in central Georgia are now coping with a disease that could further reduce their already meager yields.
The disease, caused by Phytophthora cactorum, is commonly called shuck and kernel rot because of what it does to the nuts.
Disease follows prolonged rain
"This disease appears when you have prolonged rainfall in the fall," said Chuck Reilly, a plant pathologist with the USDA Fruit and Nut Research Laboratory in Bryon, Ga. "It's caused by a fungus that is a water mold."
Researchers like Reilly believe the soil-borne disease is carried up pecan trees by pecan weevils. Adult weevils emerge from the soil during August and September and move to the developing fruit where they feed and reproduce.
Mated females climb up the trees and lay eggs within the nuts' kernels. Weevil-damaged nuts are left with small emergence holes where the grubs exited the nuts.
For the last four years, Georgia pecan orchards have been relatively free of the disease, Reilly said.
"The good news is that this disease doesn't occur every year," he said. "We have had minor incidents in five or six orchards where we have growers scouting for it. When a grower sees symptoms he knows it's time to apply a fungicide."
Makes shucks stick to nuts
The symptoms are dark brown pecan shucks, initially soft and spongy, then they dry and stick tightly to the shell. The fungal spores spread through the canopy of a tree in a cascading manner when it rains. This spreads the infection.
Reilly says if growers didn't scout for the disease and treat at the first signs, they will suffer serious losses if it makes its way into their orchards.
"The stuck-tight nuts result in a total loss for the grower," Reilly said. "If the disease keeps spreading from that point, new infections move on to the nut's kernel causing it to turn a shiny black color, rot and become rancid."
The disease may actually affect 5 to 10 percent of a grower's crop, but with no way to identify which nuts are spoiled, the grower's loss is much higher, he said.
"The good news is that south Georgia, especially the Albany area, is a little too hot for the fungus to get going," Reilly said.
Jason Brock, who diagnoses plant disease samples at the University of Georgia College of Agricultural and Environmental Sciences, hasn't identified a sample of shuck and kernel rot this year.
Disease spotted in central Georgia
"Due to the sporadic occurrence and limited distribution, this disease is not a major concern at this time," he said. "Weather conditions make this a problem more common in central Georgia, primarily Houston, Peach and Macon counties. If growers think this disease is present in an orchard, they should contact their county Extension Service agent for assistance."
Brock says growers don't need anything else to contend with on top of the crop losses they suffered from the hurricanes. Reilly agrees.
"Pecans are an alternative bearing crop," Reilly said. "This was an off year, but next year will seem like an off year too because of all the damage from the hurricanes and the potential damage from this disease."
(Sharon Omahen is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.)