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Marin IJ Articles

New threat to citrus trees

  • Wendy Irving
  • Our state has been struggling to control the glassy-winged sharpshooter, an insect that spreads Pierce’s disease in grapevines. Science and education are making some headway in that fight, but now, wouldn’t you know it, our citrus trees are being threatened by a new invader!.The Asian citrus psyllid, a vector transmitting the deadly bacterial disease huanglongbing, has arrived here in Northern California. Huanglongbing (HLB) is a death sentence, usually killing a citrus tree within five years. The good news is that little HLB has been found in California yet, but the bad news — the arrival of the Asian citrus psyllid has made the threat real.

    Since there is no cure for HLB, the only way to save our backyard trees and California’s citrus industry from it is by stopping its carrier and, unfortunately, finding and destroying infected trees. While the little psyllid, about the size of an aphid, began showing up in Southern California in 2008, HLB was first detected there just a few years ago, in 2012. Once the psyllid is present, it appears to take a few years for a tree to show the effects if, in fact, it has been infected. In recent weeks, the Asian citrus psyllid was spotted in Pacifica and South San Francisco.

    If you think you see this pest in your garden, it is important to contact the Marin County Department of Agriculture, Weights and Measures in Novato at 415-473-6700. There is also a California Department of Food and Agriculture hotline number at 800-491-1899. If the psyllid is verified, quarantines are put in place making it illegal to move citrus plants, fruit and clippings to other areas. Treatments can be recommended to kill the pest, and the watch for the potential infection by HLB should begin.

    The Asian citrus psyllid can fly short distances and be carried by the wind. However, a main way the insect spreads throughout the state is by people who transport infested citrus plants or material, so everyone in California is being asked not to move citrus about, nor bring them in from out-of-state. Purchase new citrus trees only from reputable, licensed nurseries in your area.

    So what to look for? Although you may have to use a jewelers loop or magnifying glass to spot it, the Asian citrus psyllid is easily identifiable by the waxy tubules that nymphs (juveniles) leave behind. Adults, which have brown mottled wings, feed at an unusual 45-degree angle, making them appear like little thorns on the leaves. Eggs are yellow and often found in the folds of new leaves. Be particularly watchful at times when new growth is abundant.

    The Asian citrus psyllid feeds on the leaves and stems of all citrus trees, as well as some relatives of citrus like orange jasmine and curry leaves. In fact, the first Asian citrus psyllid in the United States was found in a backyard orange jasmine (Murraya paniculata) in Florida in 1998. Help California by inspecting any citrus or related plants at least once a month.

    An early symptom of HLB is yellowing leaves. While lots of things, like nutrient deficiencies, can cause yellowing in citrus, HLB shows a more asymmetrical pattern of blotchy yellowing, often showing in just one part of the tree. As the disease progresses, fruit becomes smaller and misshapen, often staying partially green (HLB is also known as citrus greening disease). A chronically ill tree is sparsely foliated with small leaves that can point upward. The juice of the fruit is bitter, and the seeds dark. The tree eventually stops producing fruit altogether, and dies in a matter of a few years.

    Every backyard gardener is called upon to be on the lookout for the Asian citrus psyllid and HLB. You can go online to the University of California Integrated Pest Management site at www.ipm.ucdavis.edu and search “Asian citrus psyllid.” You’ll find photos and a video that will be helpful.