Marin IJ Articles

A little bug, but a big problem

• Karen Gideon

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  The female lays her eggs in the newly emerging leaves. Inspect your citrus plants by looking for developing nymphs in young leaves. Photo: UC Regents

  Marin gardeners should be on the alert for a dangerous pest. The Asian citrus psyllid is a tiny insect and disease vector that eats citrus leaves and stems.  The females lay their eggs in the new leaf growth called “flush.” As the insect munches, it injects a salivary toxin into the plant that causes the leaf tips to twist or curl and infects the tree with a killer bacterium. One Asian citrus psyllid was located in Marin County in 2018, extensive trapping was initiated and no more pests were found. But gardeners must stay vigilant. 

  The bacteria, Huanglongbing or HLB, was discovered in Asia and moved to the Americas as citrus plants were bought and sold. In Florida, the psyllid and HLB is spreading rapidly from backyards and commercial orchards with drastic impact on the citrus market there. HLB is not harmful to humans. But thousands of jobs have been lost and it has cost growers billions of dollars. HBL migrated from Mexico to Southern California in 2008 and is well established there.  

  

  The adult Asian citrus psyllid is only 4 mm or 1/16 " long. Bring a magnifying glass or loupe with you as you inspect your plants. Photo: UC Regents

  
  Fortunately, a new treatment has been developed that kills the HLB with a naturally occurring molecule found in wild citrus relatives. This molecule offers advantages over the antibiotics currently used to treat the disease in orchards. But gardener awareness and early identification of the pest is critical.

  This is where YOU, the Marin County gardener, comes in. By keeping a close watch on your citrus trees like lemons, limes, oranges, grapefruit and related plants in the Rutaceae family, such as mock orange and orange jasmine plants, you can serve as first responders.  

  
  

  

  Asian citrus psyllids feed on stems and leaves with their body at a 45 degree angle. Note the mottled coloration of the psyllid. Photo: UC Regents

  
  Observation and detection are the top priorities. The psyllid is mottled brown and about the size of an aphid. In a unique pose, the psyllid eats head down, its body tilted at a forty-five degree angle, lifting its tail high in the air. Check out the new leaf growth or new flush, because the psyllid lays its eggs there. The eggs are tiny yellow-orange and almond shaped. One female can lay several hundred eggs. The psyllids also produce a white, curlicue waxy substance that can be found on the leaves of the citrus plant.

  If you find an adult or an insect in an immature stage, contact the California Department of Agriculture Exotic Pest Line at 1-800-491-1899. 

  
  

  

  These are Asian citrus psyllids on the leaves and stems of citrus plants. Note the size and positioning of the psyllids. Photo: UC Regents

  In terms of integrated pest management, there is some biological control of the psyllid with the use of a parasitoid wasp, Tamarixia radiata. The tiny wasp lays eggs in the psyllid’s abdomen and as the eggs develop they kill and eat the psyllid.  However, the wasp needs time to become established and the effectiveness is not sufficient to prevent the spread of the insect.  

  In commercial orchards, in addition to the new molecular treatment, farmers are using many different types of insecticides and antibiotics after finding that a single insecticide isn’t effective for all stages of the psyllid lifecycle. Diseased trees must be removed in order to stop the spread to other trees on the property, the neighbor’s trees and the community. For the residential citrus-grower, a trusted arborist can guide you on what might be an effective resolution or safe tree removal.

  

  Watch for the white, waxy, curlicue substance found on the stems & leaves of citrus plants, exuded by Asian citrus psyllid nymphs. Photo: UC Regents

  Another way to protect the community and your garden from the Asian citrus psyllid and Huanglongbing disease is to purchase your citrus plants locally, being careful not to bring citrus agricultural products in from other states or countries. Not only is this practice illegal, it can create a pest problem for producers and home gardeners.

  If you find evidence of the Asian citrus psyllid in your garden, the agricultural authorities will want to inspect your citrus plants, take samples for laboratory, and possibly do some trapping or quarantining. Your cooperation is needed to determine the extent of the infestation. If you want more information on this pest, visit the UC IPM website at http://ipm.ucanr.edu/PMG/PESTNOTES/pn74155.html. For further assistance, email UCCE Master Gardeners at our Help Desk in Novato.