Since citrus greening was discovered in Florida in September 2005, growers have been on the lookout for the Asian citrus psyllid, the vector of the disease, in their groves.
Greening now is present in 12 Florida counties, said Denise Feiber, spokeswoman for the Florida Department of Agriculture and Consumer Services Division of Plant Industry, Tallahassee.
Since the disease is new to Florida, researchers still are trying to fully understand it and the vector.
“The most important research that needs to be completed is studying the psyllid-disease relationship,” said Michael Rogers, assistant professor at the University of Florida’s Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred. “We currently do not have adequate information on how the disease is transmitted by the psyllids.”
Rogers said this information is necessary to develop better management practices for psyllid and greening control because eradication is unlikely.
Psyllids favor flush
David Hall, research leader of the Subtropical Insects Research Unit at the U.S. Department of Agriculture’s U.S. Horticultural Research Laboratory in Fort Pierce, Fla., said it is not known how uniform a psyllid population may be across a grove. But population fluctuations of psyllids are closely related to flush growth.
“Psyllid populations are most abundant during the spring and early summer flush periods,” Rogers said. “These early season flushes are the time when insecticide applications for psyllid control will be most effective.”
Ron Brlansky, professor at the UF/IFAS Citrus Research and Education Center, also said that pruning provides young flush, which psyllids favor.
Chemical control options
Rogers said that UF/IFAS recommends five insecticides for psyllid control. Temik and Admire are both soil-applied insecticides, while Provado, Danitol and Lorsban are foliar-applied insecticides.
One research goal is the identification of new insecticides that can be used to manage psyllid populations.
“We have a very limited number of choices right now in terms of insecticides that are recommended for psyllid control,” Rogers said. “New products with different modes of action are needed to minimize the chances for psyllids to develop resistance to these pesticides currently being used for psyllid control.”
Also, several products that can be used for psyllid control have negative effects on the natural enemies of other potential citrus pests, Rogers said.
“Repeated use of these products could incite outbreaks of these other pests, such as scale insects, by killing off the established parasitoids that keep scale insect populations below damaging levels,” he said.
Ron Muraro, professor at the UF/IFAS Citrus Research and Education Center, said that even with additional insecticide applications and other costs of managing greening, such as removing trees with symptoms, growers still can receive a return. He said the market and fruit prices should be favorable for the foreseeable future.
Biological control options
Shortly after the psyllid was discovered in Florida in 1998, the parasitoid Tamarixia radiata was introduced for biological control of the psyllid. The parasitoid is established in many areas of the state, Rogers said.
“We are uncertain how much control of the psyllid this parasitoid is providing throughout the year,” Rogers said. “A statewide survey is underway to determine where this parasitoid is established and how much control is being provided.”
Rogers said that if it is determined that there are areas of the state where the parasitoid is not present, future releases of the parasitoid could be made in those areas if warranted.
Additional greening management
In addition to psyllid control, it is important for growers to remove and destroy trees that are infected with greening as soon as possible, Brlanksy said.
“Those infected trees serve as a source of the disease for healthy psyllids to pick up and then transmit to surrounding trees,” Rogers said.
Brlansky recommends using a foliar spray to control psyllids on infected trees prior to removal. There has been no evidence that greening is transmitted via equipment, he said.
Susan Halbert, entomologist with the Florida Department of Agriculture and Consumer Services Division of Plant Industry, said detecting greening is difficult.
Halbert said trees infected with greening have blotchy mottling on the leaves that can be mistaken for a nutrient deficiency, so it is important to keep trees well fertilized for micronutrients.
If you think a tree may have greening, check for notches on the leaves, which may indicate that psyllids are present, she said.
Also, most fruit from infected trees falls off, Halbert said. Fruit is small, lopsided and has poor color and taste.
If you think you might have greening in your grove, call the Florida Department of Agriculture and Consumer Services greening hot line. If you are located in Broward, Miami-Dade, Monroe and Palm Beach counties, call (800) 850-3781. For all other Florida counties, call (800) 282-5153.
Future greening research
Researchers in Florida are prohibited from possessing and working with greening in the laboratory, Rogers said. If this situation is amended, Rogers thinks researchers can begin to better understand greening.
“We are collaborating with researchers at quarantine facilities outside of Florida to try and complete some research to answer some of the questions about the psyllid-disease interaction,” Rogers said. “Hopefully, if the regulatory status of the disease is amended to allow researchers to work directly with the pathogen in secure facilities within the state of Florida, we can quickly gain a better understanding of how to manage this disease.”
For more information
Florida Department of Agriculture and Consumer Services Citrus Greening hot line
• Broward, Miami-Dade, Monroe and Palm Beach counties: (800) 850-3781
• All other Florida counties: (800) 282-5153
Recommended insecticides for psyllid control
• Admire (imidacloprid): applied as a soil drench to bearing and nonbearing trees less than 8 feet in height
• Temik (aldicarb): soil incorporated for use on both bearing and nonbearing trees in the field; can only be applied between Jan. 1 and April 30.
• Danitol (fenproprathrin): foliar applied for use on both bearing and nonbearing trees
• Lorsban (chlorpyrifos): foliar applied for use on both bearing and nonbearing trees
• Provado (imidacloprid): foliar applied for use on both bearing and nonbearing trees