If you have citrus trees in your garden, or know someone who does, listen up. A pest insect that has wiped out half of the citrus crop in Florida is spreading in California and has reached the Bay Area. Last year, a new quarantine area was created in the San Jose region, because the pest was found in trees there. Now the most recent quarantine area covers the northern peninsula and a swath of the southern part of San Francisco.
Lemons on a Healthy Lemon Tree in San Francisco
The insect itself will not kill the tree, but it often carries a deadly disease, and if a particular individual insect is carrying that disease, it will infect the tree while it is feeding. And then there is no cure. Other Asian citrus psyllids will pick up the disease from that infected tree, and will spread it.
So far, none of the insects found in our region have been carrying the disease, but it seems like only a matter of time till one does. Scientists are looking for a cure, or a way to breed resistance to the disease into citrus trees, and would like to buy as much time as they can by keeping the problem in as small an area as possible.
What to do? Inspect your trees. Spring is a good time to do it, since it is a time when there is much active growth on citrus. Look carefully at as many of the growing tips, with their small, new leaves, as you can. The insect, which is called the Asian Citrus Psyllid, or ACP, lays very small yellow-orange eggs in new growth. They will be easier to see with a magnifying glass. The eggs hatch into yellow nymphs that average sesame seed-sized. They are also distinctive in having long, white "tubules" with bulbous ends that extend from their bodies. The adults are aphid-like, mottled browns, and stand with their rear in the air, heads down, sucking sap.
Asian Citrus Psyllid Nymphs
Asian Citrus Psyllid Adult Feeding on Citrus Leaf
If you find the insect on your tree, and are not in an area already quarantined, you should call the California Food & Agriculture (CDFA) Exotic Pest Hotline at 800-491-1899. If you are within the quarantine area already, you should try to kill the pest.
To see an interactive map of the quarantined areas and more photos and learn the best ways to control the pest, see the following UC website: http://ucanr.edu/sites/ACP/Homeowner_Options/
Also, be sure to buy citrus only from responsible sources. (Major citrus tree growers are now growing trees for the market only in covered production areas that the pest can't get into.) Don't accept plants, cuttings, or grafting material from other gardeners.
And if you are in a quarantined area, don't take any leafy branches outside of it. (You can share your fruit outside of the quarantined area if it doesn't have any stems or leaves attached.)
The insect can also infest some plants that are related to edible citrus, like calamondin (xCitrofortunella microcarpa), box orange (Severinia buxifolia), orange jessamine or orange jasmine (Murraya paniculata), and Indian curry leaf (Murraya koenigii). They should also be inspected and are subject to the same quarantine rules.
The disease we are trying to avoid, and that I hope we never see, is Huanglongbing, or HLB. It is also known as yellow shoot or yellow dragon disease. The leaves of infected trees have yellow blotches, usually starting in one section of the tree. The blotches don't look like most nutritional deficiencies in that they cross the leaf veins, and are often arranged asymmetrically on the leaf. Fruit develops unevenly, asymmetrically, ripens poorly, with little juice and a bitter flavor. The disease will kill the tree. If it appears, the only recourse at this time is to remove the infected tree before the disease spreads to other ones.
So let's get out there and look now, before it's too late!
Yellow-blotched Leaves of a Citrus Tree Infected with HLB Disease.