International air travel is a wonderful thing, especially if you happen to be an insect. Just ask the Asian citrus psyllid. Thanks to hitching free rides on airplanes, where it typically stows away in galleys and lavatories, this infamous insect has journeyed to the four corners of the globe, becoming a universal nemesis of citrus trees in the process. In Florida, in just twenty years, citrus acreage has been reduced by half due to the Asian citrus psyllid.
It is to help prevent a similar catastrophe from happening here that I am writing about this insect, which is related to aphids and is of similar size. It is the vector of a bacteria, carried in its saliva, that turns ripe citrus fruit green, and so the malaise is known as citrus greening disease.
Yellow blotches around leaf veins are another symptom and so it is also called yellow dragon disease, a translation of huanglongbing (HLB). Symptoms also include misshapen fruit and excessive fruit drop.
There is no cure for this disease, just like there is no cure for oleander leaf scorch, another devastating bacterial disease spread by an insect. A citrus tree may survive for up to eight years following infection with HLB, but it should be removed immediately once symptoms are observed. The challenge of getting the word out is enormous since 60% of California homeowners have at least one citrus tree somewhere around the house.
If you have a tree that appears to be infected, immediately call the California Department of Food and Agriculture pest hotline at 800-491-1899.
The pysllids themselves are most noticeable on young leaves which is a good argument for minimizing pruning, which stimulates new growth. If you do prune, double bag clippings before placing them in the trash. Purchase citrus trees from reputable nurseries and do not take
your fruit outside your immediate area.
The first local case of HLB was discovered on a pomelo tree in Hacienda Heights in 2012. Since then, 500 cases have been reported in the Los Angeles area, 300 of those in the last year. Infected trees have also been found in Cerritos, La Puente, Norwalk, Pico Rivera, Rosemead, San Gabriel, and Whittier.
Since the disease has no cure, control of the Asian citrus psyllid appears to be the best way of addressing this crisis.
Past successes with control of major insect pests may come into play. Some may recall the Mediterranean fruit fly scare from thirty years ago. Helicopters regularly sprayed Malathion over certain Los Angeles neighborhoods — to their residents’ chagrin — until a biological solution was found.
Vast numbers of fruit flies were raised in captivity and then the males were sterilized through radiation and released. A female fly that mated with a sterile male would not give birth and so the fruit fly problem was soon controlled. In the case of local ash whitefly and eugenia psyllid infestations, parasitic wasps specific to each of these pests were raised and released en masse, bringing the pests to heel.
Raising broods of Asian citrus psyllids and sterilizing the males, as well as introduction of hordes of predatory insects have been suggested as means for preventing spread of HLB. Finally, culturing fungal pathogens that cause psyllid death and then spraying those fungal cultures onto citrus trees is being evaluated as an HLB control measure.
Tip of the Week: There are two non-toxic means available to the homeowner for discomfiting Asian citrus psyllids and other sap-sucking insect pests. The first is to procure insects that prey on psyllids — including ladybugs, syrphid flies, parasitic wasps, lacewings, and predatory mites — and release them into your citrus trees. You can find these through online vendors. You can also prevent ants, which benefit from honeydew producing insects such as psyllids, aphids, whiteflies, and mealybugs, from getting into your trees by slathering a sticky paste such as Tanglefoot on their trunks or by placing Borax based ant-bait stations in your garden. Ants fight off the beneficial, predatory insects mentioned above and so ant prevention is a key component of insect pest control in the garden at large.