Home & Garden

Tiny insect threatens citrus statewide

It seems amazing that a tiny insect the size of an aphid is a threat to the entire citrus industry in California as well as to the citrus trees in our backyards. The Asian citrus psyllid is a carrier or vector of a bacterium associated with the fatal citrus disease huanglongbing or HLB, also known as citrus greening disease. The psyllid ingests the bacteria as it feeds on infected trees and then injects the bacteria into new green growth on healthy trees. Citrus trees infected with the bacteria eventually die and as yet there is no known cure for HLB.

The Asian citrus psyllid spread from Asia or India and arrived in Florida in 1998. The bacteria it carries now infects commercial citrus orchards in 31 counties in Florida. The disease has since spread (in transported nursery stock) first into Southern California, mostly in backyard urban and suburban trees, and has now been detected in the central San Joaquin Valley and further north leading to the formation of quarantine zones which include portions of Fresno, Madera and Tulare counties. For maps of the zones, go to www.CDFA.ca.gov/QuarantineBoundaries.

Because so many of the infected trees have been found in backyard gardens, home gardeners can act as primary first detectors of the presence of Asian citrus psyllids. The psyllids feed and lay their eggs on young leaf ‘flushes’ in mature citrus trees in spring and fall; lemons and young citrus trees can have several flushes throughout the growing season. The tiny yellow-red almond-shaped psyllid eggs are laid inside the folds of tender new leaves. The eggs hatch into nymphs that feed only on soft leaf tissue and immature stems. Using a hand lens can help with identification. As the nymphs suck out sap, they excrete copious amounts of sugary ‘honeydew’. The waxy tubes that the nymphs create to carry away honeydew waste are unique to the Asian citrus psyllid. Check the UCDavis IPM website, www.ipm.ucanr.edu, Pest Note publication 74155 which has detailed descriptions and photos of the psyllid adults, nymphs, waxy tubes, and leaf and tissue damage.

Home gardeners should monitor their citrus trees whenever new leaf flushes appear, looking for damaged or twisted new shoots and leaves, psyllid eggs and nymphs inside new leaf folds, waxy tubes near the feeding sites, sticky honeydew and the ants that feed on the honeydew, and sooty mold, a black residue of honeydew on the fruit surface. Call the CDFA Exotic Pest Hotline immediately at 1-800-491-1899 if you suspect you’ve found evidence of the Asian citrus psyllid. Staff can determine if Asian citrus psyllids are new or common in your neighborhood. The CDFA may treat the infestation with insecticides if psyllids are new in the area. If they have become a common problem, home gardeners can get advice on treatment from the Fresno County Master Gardeners hotline 559-241-7535, 9 a.m.-noon Monday-Friday or their website, www.ucanr.edu/sites/mgfresno.

Other important steps to prevent the spread of Asian citrus psyllids is to maintain a healthy balance of beneficial insects to prey on the psyllids in our gardens, to control for ants that “herd” the psyllids to feed on the honeydew and to respect quarantine rules regarding the buying or transporting of citrus from or into quarantined areas.

Send Elinor Teague plant questions at etgrow@comcast.net or features@fresnobee.com (“plants” in the subject line).