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Citrus pest continues to thrive in Valley Center



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April 30, 2014
A pest known as the Asian citrus psyllid has made its way into Valley Center, threatening citrus trees throughout the area. The only way to control the pest is to treat or remove the trees according to Citrus Pest and Disease Prevention Program representative Bob Atkins.

The psyllid, which is a small insect similar to an aphid, makes its home on citrus trees carrying a disease called Huanglongbing or HLB, according to Atkins.

"They're very hard to see, about the size of a grain of pepper," said Atkins. "The adults are unique in that while they are feeding on the plant, they sit at a 45 degree angle. They almost look like a thorn on the branch of a citrus tree. The juveniles, called nymphs, are even smaller."

Because of its size the psyllid can be hard to spot by the layman. Nymphs can usually be found on the newest growth of the plant, usually in the spring or fall.

"They are a bright yellow-orange color, but it takes a trained eye to see them," said Atkins.

This invasive species comes from Asia where the problem has existed for over a hundred years. The pest was found in Florida and Brazil in the early 2000s. In 2008 it was found in California, Atkins said.

"It made the leap from Asia into the new world," said Atkins, noting that genetic testing can be done of the psyllid to determine where it originated. "It's most likely that our population came up from Mexico; people bring them in floral bouquets where they travel on cut foliage or firewood that is smuggled in to California."

Trees don't usually show symptoms they are affected, according to Atkins. But growers who are familiar with their trees may notice some twisting in the new foliage.

"It doesn't look much different from the damage they see with aphids," he said. "It's really a subtle change."

Atkins said the concern isn't the insect as much as the disease that it carries.

"If it were only the insect we wouldn't be concerned," he said. "We would treat it like we do any other insect that is partial to fruit trees. It is the bacterial disease, HLB that they carry."

Once a tree contracts HLB there is no cure other than to remove it.

"Once the tree is infected, it's fated to die," said Atkins. "Before it does, it goes through a latency period where it's still infected and it can pass the infection on either by graft or by the psyllid itself. It's very difficult to find the bacterium in the plant."

According to Atkins, HLB can sit undetectable in a plant for up to four years. Symptoms and signs, which include yellowing of leaves and inedible fruit, do not appear until the disease is full-blown.

"It's still infectious during that whole time," he said. "That's why I call it a monster disease."

To control the spread of the insect, Atkins recommends trees be treated by citrus pest and disease prevention.

"For residential areas the best thing the homeowner can do is control the ant population," he said. "It helps control all of the other insects we have because the ants collect the honeydew they produce and keep the nymphs in their colonies."

Commercial growers should contact the Citrus Pest and Disease Prevention Program for treatment of their groves.

"We are organizing treatment areas where everybody in the treatment area treats their groves at least twice a year," said Atkins. "We try and time those treatments so everybody puts the treatment on at the same time, within a two to three week period of time."

Treatment times occur just before the fall flush, when the population of the psyllid is at its highest, usually in July or August and then again before the spring flush which is usually in February when the population is at its lowest and mostly adults.

Atkins said the chemical is injected into the soil and watered into the plants.

"We time it very carefully so we avoid the bloom and we are doing it just before that new growth on the tree, that fall flush," Atkins said. "Since that is when the insect feeds, we are looking to have the greatest amount of insecticide inside that foliage when their populations are highest."

Homeowners should go to their local garden center to see what treatments are available. To contact the Citrus Pest and Disease Prevention Program or for more information on the Asian citrus psyllid, visit www.californiacitrusthreat.org.

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