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How you can help stop the spread of a citrus-killing pest

This photo shows the yellow blotches associated with Huanglongbing caused by Asian citrus psyllid.
This photo shows the yellow blotches associated with Huanglongbing caused by Asian citrus psyllid.

Q: How is the fight going against Asian citrus psyllid?

Matt, Cayucos

A: Asian citrus psyllid (ACP) was first detected in San Diego County in 2008. Since then, county agriculture departments, the California Department of Food and Agriculture (CDFA), UC Cooperative Extension and citrus growers have made measurable strides towards limiting its spread.

The most visible part of their efforts includes yellow sticky traps placed in homeowners’ citrus trees by county agriculture workers. The traps are inspected regularly for the presence of ACP adults.

ACP is mottled brown and the size of an aphid, approximately an eighth of an inch long. It damages citrus trees by feeding on leaves, injecting a salivary toxin that causes the new leaf tips to twist or burn back.

Feeding damage alone will not kill trees. But the bacteria it can transmit can cause the deadly disease Huanglongbing (HLB), for which there is no cure. It can kill a citrus tree in as little as five years. Although ACP has been found in San Luis Obispo County, HLB has not.

Researchers have found a biological control agent, a parasitic wasp from the Punjab of Pakistan, that attacks ACP nymphs. The parasitic wasp is Tamarixia radiata, and after extensive testing and evaluation, the wasp was released in Southern California. It is currently being monitored for its ability to establish its own population and manage ACP populations. If the wasp proves to be successful in controlling or limiting the spread of ACP, it will be released throughout California, including San Luis Obispo County.

Another control method being tested by the state Department of Food and Agriculture is residential insecticide treatments designed to control the psyllid. This is in limited areas and is not now available in San Luis Obispo County. For home use, the state department is recommending a soft foliar insecticide such as oils and soaps (horticultural spray oil, neem oil, insecticidal soap) that can help reduce psyllids by killing them and deterring them from laying eggs. These insecticides are generally lower risk to beneficial insects (natural enemies and pollinators).

Homeowners can help authorities by inspecting new growth on their trees. If you suspect you have ACP, please call the CDFA Exotic Pest Hotline at 1-800-491-1899.

For more information about ACP, HLB and Tamarixia radiata, visit the UC Riverside Center for Invasive Species Research blog, http://cisr.ucr.edu/blog/.

Leonard Cicerello is a UCCE Master Gardener.

Got a gardening question?

In San Luis Obispo call 781-5939, Arroyo Grande, 473-7190 and Templeton, 434-4105. Visit us at http://ucanr.org/sites/mgslo/ or email us at anrmgslo@ucanr.edu. Follow us on Instagram at slo_mgs and like us on Facebook. Informative garden workshops are held the third Saturday of every month, 10 a.m. to noon at 2156 Sierra Way, San Luis Obispo. Garden docents are available after the workshop until 1 p.m. To request a tour of the garden, call 781-5939.

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