- Huanglongbing disease is the HIV of the citrus world, says University of Florida entomologist Michael Rogers.
- HLB is one of the most significant citrus diseases worldwide due to difficulties in disease management.
- HLB-related tree death is usually not caused by the disease alone. A feeding psyllid punctures the tree’s phloem which increases the tree’s susceptibility to other citrus-related pests and diseases which speed up the tree’s decline and eventual death.
RESEARCHERS COLLECT yellow sticky pest traps looking for the Asian citrus psyllid.
“This was our first mistake,” Rogers reflected. “We wanted to break the psyllid’s life cycle by knocking out all nymphs and allowing the adults to die of old age…When you get nymphs on new flush, even with the best coverage, you get 85 to 90 percent nymph control but you still miss some.”
Florida has placed a strong emphasis on the protection of young citrus trees. In a UF trial, three soil-applied systemic insecticides – Admire Pro, Platinum 75 SG, and Belay 50 WDG – were applied every six weeks to young trees. Belay can only be used in non-bearing citrus in Florida, Rogers says.
The trial results showed long-lasting systemic protection of the entire tree, control of the psyllid and leafminer pests, and the disruption of psyllid feeding which reduces HLB pathogen transmission.
Other areas of Rogers’ work include the application of integrated pest management (IPM) for psyllid control where natural insect predators kill the psyllid. The parasitoid Tamixaria radiatawas first introduced in Florida in 1999 after importation from Taiwan and Vietnam. The Tamixaria population was tracked from 2006 and 2007 to determine actual population numbers.
The Tamixaria level never reached above 20 percent except for a brief period at 50 percent. Overall, Rogers says the parasitoid failed to provide suitable biological control for effective psyllid control.
“There have not been many promising solutions in biological control when dealing with an insect-vectored pathogen; especially in citrus since it’s a perennial crop,” Rogers explained.
“We have trees in the field year-after-year which are constantly exposed to potential HLB infection by the psyllid,” the entomologist said. “The real threshold for psyllids is zero. Bio-control is better suited in general where some level of damage can be tolerated. We cannot tolerate any psyllids in citrus.”
Other Rogers trials suggest broad-spectrum insecticides applied to foliage are effective in adult psyllid control, Rogers says. These applications target adults before the flush cycle begins which eliminates reproduction. It is far easier, he says, to control a small population versus expanding numbers.
“We gain nearly a 100-percent death rate in adults with foliar applications with pyrethroid products,” Rogers said.
The complete list of the tested pyrethroid products and results is available in the Florida Citrus Pest Management Guide located on the Citrus Research Education website at www.crec.ifas.ufl.edu/extension/pest/.
Rogers also discussed Florida’s Citrus Health Management Areas (CHMA) established early last year. A CHMA (CHEE-MUH) is an area where citrus producers voluntarily coordinate psyllid control efforts to achieve higher levels of control. This is better than a grower can gain individually and also prevent insecticide resistance through the coordinated rotation of pesticide modes of action.
“Psyllid populations in CHMAs have decreased where coordinated insecticide applications have been implemented,” Rogers said. “Florida’s citrus industry has benefitted from everyone working together.”
Statewide, 38 CHMAs cover more than 486,000 acres of commercial citrus. Federal and state citrus experts scout about 6,000 blocks over a three-week period; equivalent to 106,000 acres per scouting cycle.
Additional CHMA information is available at www.flchma.org.