Citrus greening is another headache for the Florida grower. But, University of Florida researchers are trying to ease the pain.
The UF research program will attack the citrus greening problem in three ways: by developing best management practices for the bacterial disease; improving diagnostic methods; and testing the effectiveness of systemic insecticides to stop transmission of the disease by psyllids, according to Ron Brlansky, a professor of plant pathology at the UF/Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.
Brlansky said early symptoms such as leaf mottling and yellow discoloration may be mistaken for nutritional deficiencies, and laboratory tests are needed to determine the problem. The disease can also be identified by cutting open small and poorly colored fruit and looking for aborted seeds, according to a university news release.
Brlansky is working with Michael Rogers, an assistant professor of entomology at the Lake Alfred center, and Vern Damsteegt, an entomologist at the U.S. Department of Agriculture’s Foreign Disease and Weed Science Research Unit in Fort Detrick, Md., to evaluate the ability of systemic insecticides to reduce transmission of the disease by psyllids.
Unlike broad-spectrum insecticides that are applied to the foliage of citrus trees, soil-applied systemic insecticides may not disrupt the effectiveness of other beneficial insects that control citrus pests in existing biological control programs, Rogers said.
“Recent results in our field trials have demonstrated that soil-applied systemic insecticides such as Aldicarb can reduce psyllid populations on mature citrus trees and provide a significantly longer period of control than foliar applications,” he said. “These research projects will allow us to manage psyllids with fewer pesticide applications than growers use in other regions of the world where greening is a problem.”
Rogers said they are looking at the ability of psyllids to transmit the bacterium between diseased and healthy plants that have been treated with systemic insecticides. “We know the psyllids are killed when they feed on trees treated with systemic insecticides, but we do not know if acquisition and transmission of the disease will occur,” he said.
The effectiveness of the beneficial wasp in controlling the Asian citrus psyllid is being evaluated by Rogers in cooperation with Phil Stansly, a professor of entomology at the UF/IFAS Southwest Florida Research and Education Center in Immokalee, and David Hall, an entomologist at USDA’s Horticultural Research Laboratory in Fort Pierce.
The study will identify citrus-production areas where the beneficial wasp is established and determine when it is providing effective biological control of the psyllid and when broad-spectrum foliar insecticide sprays should not be used. The wasp will be released in groves where the biological control is not yet established.
“Until we can develop citrus cultivars that are resistant to greening, the disease will have to be actively managed,” Brlansky said. “These management strategies include the use of certified disease-free nursery trees, frequent inspections for the disease and removal of infected trees that serve as a source for new infections.”
He said the management program also includes educating growers about identifying symptoms that are difficult to diagnose because they often occur in conjunction with mineral deficiency symptoms.
To improve diagnostic methods, Brlansky is working with Michael Davis, a professor of plant pathology at UF’s Tropical Research and Education Center in Homestead, and John Hartung, a plant pathologist at USDA’s Fruit Laboratory in Beltsville, Maryland.
“If we can culture the citrus greening bacterium in the laboratory, then we would have another valuable tool for diagnosing the disease,” Brlansky said. “Having the bacterium in a culture would enable other diagnostics such as antibodies for serological detection to be developed. We are also looking at the presence of the bacterium in non-symptomatic tissues.”
Source: University of Florida/Institute of Food and Agricultural Sciences