MANAGEMENT - Asian Citrus Psyllid

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This article is to inform home gardeners and others of the danger of the Asian citrus psyllid (ACP), Diaphorina citri, insect that can infest and kill all varieties of citrus.
by Maple Tree · All Zones · Insects · 0 Comments · April 29, 2016 · 3,658 views

IDENTIFICATION OF THE HLB DISEASE
In March 2012, huanglongbing was found in a citrus tree in Southern California, and this tree was destroyed to prevent the spread of this disease. Everyone’s assistance is needed to watch for additional infected trees. The disease may have already spread from this initial infection in Los Angeles in the bodies of psyllids to other citrus trees, or it may come into the state in an infected citrus tree or other host plant, illegally imported or smuggled into the state.
It could also arrive in the body of an infected psyllid that flies or rides on a plant into California from places such as Mexico where HLB and psyllids are found together. The tree that was found with HLB in Los Angeles is believed to have been infected through grafting a bud (taking plant tissue from one tree and inserting it into another to form a new branch) from another infected tree.
An early symptom of HLB in citrus is the yellowing of leaves on an individual limb or in one sector of a tree’s canopy. Leaves that turn yellow from HLB will show an asymmetrical pattern of blotchy yellowing or mottling of the leaf, with patches of green on one side of the leaf and yellow on the other side. Citrus leaves can yellow for many other reasons and often discolor from deficiencies of zinc or other nutrients. The pattern of yellowing caused by nutrient deficiencies typically occurs symmetrically between or along leaf veins.
As the disease progresses, the fruit size becomes smaller, and the juice turns bitter. The fruit might remain partially green, which is why the disease is also called citrus greening. The fruit becomes lopsided, has dark aborted seeds, and tends to drop prematurely.
Chronically infected trees are sparsely foliated with small leaves that point upward, and the trees have extensive twig and limb dieback. Eventually, the tree stops bearing fruit and dies. Fruit and tree health symptoms might not begin to appear until two to three years after the bacteria infect a tree.

DAMAGE
The Asian citrus psyllid damages citrus when its nymphs feed on new shoots and leaves (flush growth). They remove sap from the plant tissue and inject a salivary toxin as they feed. This deforms new leaves by twisting and curling them and inhibits or kills new shoots by burning them back.
There are many other insect pests that can cause twisting of leaves such as aphids, citrus leafminer, and citrus thrips. The twisting of leaves doesn’t harm trees and can be tolerated, but the burning back of new flush will retard the growth of young trees that are less than five years old.
Excess sap, or honeydew, that the nymphs excrete accumulates on leaf surfaces. This promotes the growth of sooty mold, which is unsightly but not harmful. Other insect pests of citrus also excrete honeydew, including aphids, whiteflies, and soft scales.
Most importantly, the Asian citrus psyllid can kill citrus trees through its feeding activity if the insect infects the tree with the bacterium that causes huanglongbing.

MANAGEMENT
In response to the establishment of ACP in California, the California Department of Food and Agriculture (CDFA) initiated an extensive monitoring program to track the distribution of the insect and disease. This program involves CDFA and other personnel regularly checking thousands of yellow sticky traps for the psyllid, in both residential areas and commercial citrus groves, in locations where the psyllid may be spreading. The program also includes frequent testing of psyllids and leaf samples for the presence of the pathogen.
Results are being used to delimit quarantine zones, guide releases of biological control agents, and prioritize areas for a residential chemical control program. As the psyllid has spread into new areas, monitoring and control resources have been reallocated. In some areas, home gardeners will need to take an active role in monitoring for the psyllid and disease, and take steps to protect their own trees.
Psyllid Detection and Quarantine
As part of the monitoring program, citrus trees are examined to find the psyllid, and yellow sticky cards are hung in trees to capture adults. When a psyllid is found, a quarantine zone is established in the surrounding area. Plants and fruit that could be hosts of the psyllid (i.e. citrus and close relatives) can’t be taken out of this area. Quarantine helps prevent psyllids from being moved to new, uninfested areas of California.
Whether you are inside or outside a quarantine area, it is very important to assist with the effort to detect and eradicate the Asian citrus psyllid. Your efforts will reduce the potential for this psyllid to spread huanglongbing and will provide more time for scientists to work on finding a cure for the disease. For maps and information about the quarantine areas, see the CDFA Web site (PDF) or the UC Web site.
UC citrus entomologist Beth Grafton-Cardwell, Ph.D., explains how to monitor citrus trees for Asian citrus psyllid. (1:00)




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