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Gardening tips: How to prevent the spread of citrus disease

The Asian citrus psyllid is about one-eighth of an inch long and can spread a bacteria that can kill citrus trees.
The Asian citrus psyllid is about one-eighth of an inch long and can spread a bacteria that can kill citrus trees. Special to The Bee

Huanglongbing (HLB) or citrus greening disease is now a very serious threat to the citrus industry and to backyard citrus trees in California.

HLB is a bacterial disease, fatal to citrus trees, carried by the Asian citrus psyllid, a very small winged insect about the size of an aphid. Home gardeners can help limit the spread of the psyllid and HLB by becoming the first detectors of the presence in their neighborhood of the Asian citrus pysllid. Because the psyllid has been found in Fresno and Madera counties, most of these areas are under quarantine by the California Department of Food and Agriculture. Citrus cannot be transported into or out of the area.

Adult psyllids can be identified by their “bottoms up” position as they feed. The psyllids lay their tiny, yellowish oval eggs in the folds of the first flush of new leaves on all varieties of citrus – oranges, lemons, limes, tangerines, etc.. Mature citrus trees flush new leaves in spring and fall; young trees will produce new leaves during warm spells as well.

Regularly monitor for HLB by checking the new leaves on all sides of your citrus trees this spring for any signs of Asian citrus psyllid infestation. First, pull open the new leaves and use a magnifying glass to help find eggs. The eggs hatch into tiny nymphs, and the nymphs, which feed only on tender new leaf tissue, inject a toxin into the tissue that causes the young leaves to twist and develop notched edges. The nymphs also excrete copious amounts of sticky “honeydew” which attracts ants and they produce thin waxy tubes from their rears to carry away the honeydew.

When monitoring your trees, you’ll be looking for adult psyllids that look like winged aphids but which feed at a distinct 45-degree angle, for tiny almond-shaped yellowish eggs hidden in the folds of the first flush of new leaves, for twisted and notched new leaves, for sticky honeydew and the ants that feed on the honeydew, for small waxy tubes and for sooty mold, a fungus which forms on the honeydew.

Symptoms of HLB in infected trees include unevenly mottled, yellowing leaves on one side of the tree. As the disease progresses, twigs and limbs die, the fruit gets smaller, stays green (the reason for the name citrus greening disease) and develops a bitter taste. Within five years, the tree will die back completely.

It can take a couple of years after the psyllids have injected the deadly bacteria for citrus trees to show the symptoms of HLB. Home gardeners’ efforts to identify and treat for the insect carrier of HLB can have a great effect on curtailing the spread of the disease.

If you suspect that your trees may have an infestation of the Asian citrus psyllid, call the CDFA Exotic Pest hotline, 1-800-491-1899 or the Fresno County Master Gardeners helpline (559) 241-7534, M-F, 9 a.m. to noon.

Note: Once again, Plant a Row for the Hungry or PAR is collecting citrus to be donated to the Community Food Bank. This year the collection will be on Saturday, Feb. 2, at the Garden of the Sun, NE corner of Winery and McKinley in Fresno, from 9-11 a.m. There is also a free citrus class given by Fresno County master gardeners at 9:30 a.m..

Because of the quarantine for the Asian citrus psyllid in our area, please remove all leaves and stems from donated citrus before delivery.

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

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