Citrus greening, spread by the Asian citrus psyllid, has devastated millions of acres of citrus in the United States and around the world. With citrus trees a staple of Southern California gardens — and with much of Long Beach within the quarantine area, Long Beach Organic hosted a presentation Saturday on how gardeners can help control the outbreak.
Master gardeners Hilda Gayton and Mary Pierson stressed that there is no cure for Huanglongbing (HLB), which has killed over half of Florida’s commercial citrus groves since arriving there in 1998. Believed to have arrived in the U.S. as a result of an illegal graft, the disease was first detected in California in 2008.
“It’s here and it’s killing our trees,” said Gayton. “There is no cure. There is only prevention. The important thing is to share the information.”
The psyllid lays its eggs on new growth in citrus trees, and the resulting nymphs suck on the leaves, leaving them notched and yellow. Gayton said catching the nymphs before they turn into winged adults is the best strategy for control, since adults can fly one mile in two weeks, potentially spreading the disease over a wide area.
The nymphs are yellowish-orange with white tubules, and about the same size as aphids. You can use a magnifying glass or your smartphone to detect nymphs. Gayton recommends cutting off the affected area of the tree.
You should also notify the California Department of Agriculture, which, depending on the situation, may come to the location to set traps, test for the disease, and remove any infected trees. Although Gayton said it’s hard to have a tree cut down, an infected tree would die within about three years anyway.
Signs your citrus trees may be infected include yellowed, notched leaves and misshapen fruit with dark seeds. But Gayton said often by the time these symptoms appear, the disease is in full force.
Typical organic control methods like neem oil, peppermint oil, companion plantings, and predatory insects are ineffective in killing the psyllids, and even nonorganic systemic poisons such as Bayer are only effective for a month at a time.
The University of California Integrated Pest Management Program is experimenting with a tiny parasitic wasp called Tamarixia radiata, which lays its eggs underneath the psyllid nymph eggs and devours them when they hatch. However, the psyllids’ sticky honeydew excretions attract ants, which can drive off any beneficial insects.
In such an environment, it’s imperative not to move plant materials and to clean gardening tools with an alcohol or bleach mix after use. “At the end of the day, it’s about being thoughtful about the community,” Pierson said.
CaliforniaCitrusThreat.org advises gardeners to: