The citrus disease HLB, also known as citrus greening, has a formidable enemy in a fungal pathogen, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers reported. The fungus is Cordyceps javanica, strain Apopka, discovered by research scientist Lance Osborne in the mid-1980s. The fungus was isolated from dead insects on plants in a greenhouse at the UF/IFAS Mid-Florida Research and Education Center in Apopka.
Spores of Cordyceps javanica grow in bead-like strands across citrus leaves, attaching themselves to the body of HLB-spreading Asian citrus psyllids (ACP). They germinate and infect the psyllids, effectively lowering pest numbers by up to 90%. The fungus sustains itself and its impact on the psyllids for two full weeks after its application.
Scientists at two UF/IFAS research centers published their Cordyceps javanica findings in the Sept. 14 issue of Insects.
“Growers must control the psyllid to produce fresh fruit,” said Pasco Avery, a UF/IFAS Indian River Research and Education Center scientist in Fort Pierce. “What the growers need is an integrated pest management program to mitigate the psyllid populations, minimize the input of non-selective insecticides, and preserve the lady beetles, lacewings and parasitic wasps that are the psyllid’s natural enemies.”
Avery said the psyllid develops resistance to synthetic broad-spectrum chemical insecticides. Therefore, an integrative pest management program is needed. Scientists can employ a combination of tools such as the fungus C. javanica, along with the psyllid’s natural enemies, to protect citrus trees.
To measure the effectiveness of the fungus, Avery employed a tap-sampling method to collect psyllids present on citrus trees before and after the fungus was applied.
Avery and his colleagues mixed a powder form of the fungal product with water and white oil and used agricultural blast sprayers to apply the viable spores to the trees. Also, a biorational insecticide called spinetoram was mixed with white oil and applied to other trees in the same grove as a comparison.
The field experiments took place in 2018 and 2019 at The Florida Research Center for Agricultural Sustainability in Vero Beach.
“The field study in 2018 indicated that C. javanica alone, C. javanica mixed with white oil, and spinetoram mixed with white oil suppressed the psyllid populations by 60 to 90% and 61 to 83%, seven and 14 days after application,” said Avery.
Avery said only spinetoram plus oil subdued the psyllids 100% up to seven days after the fungus was applied in the 2019 study. Lady beetles that eat ACP were observed foraging in the citrus trees throughout both studies.
“The fungus C. javanica is compatible with the environment, the psyllid’s natural enemies, and it suppresses psyllid populations that vector the pathogen associated with the citrus greening disease,” Avery said. “We recommend it as part of citrus growers’ integrated pest management strategies.”
Source: University of Florida Institute of Food and Agricultural Sciences
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