Nature May Protect Arizona’s Citrus From Tree-Killing Disease

By Amanda Solliday
Published: Wednesday, August 19, 2015 - 8:59pm
Updated: Thursday, August 20, 2015 - 8:29am
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(Photo by Amanda Solliday - KAWC)
Glenn Wright, associate professor and fruit tree specialist at the University of Arizona’s Yuma Agricultural Center, manages a screenhouse that protects 49 varieties of citrus plants from the Asian citrus psyllid.
(Photo courtesy of U.S. Department of Agriculture)
Example of citrus greening leaves.
(Photo courtesy of USGS Bee Inventory and Monitoring Lab)
Citrus psyllid.

Eight new cases of citrus greening have popped up in the past month near Los Angeles, according to the California Department of Food and Agriculture. The tree-killing disease is also damaging groves in Florida and Texas, but has yet to appear in Arizona.

Researchers want to know if climates like Arizona’s offer citrus trees some natural protections against greening.

When a small insect called the Asian citrus psyllid feeds on trees, it can transmit citrus greening. The bacterial disease causes a decline in fruit quality and eventually kills the infected tree.

In Arizona, the psyllid has been spotted in commercial groves in Yuma County and on residential trees as far north as Maricopa County. But so far, none of these insects carry the disease.

“Arizona is the last major citrus producing state that does not have, has not been affected by greening. And it is in an unenviable position because of that," said Glenn Wright, fruit tree specialist at the University of Arizona’s Yuma Agricultural Center.

Wright said nature may protect Arizona’s citrus from the disease.

Research in Brazil shows greening is less common in hot areas compared to cooler parts of the country. And other scientists have placed infected young tree branches in a heat chamber set around 110 degrees.

"It can just eliminate the bacteria altogether. So that kind of brings hope," said Wright.

Heat can also change how citrus trees grow. Wright said high temperatures paired with low humidity slows growth during the summer. And psyllids prefer to feed on new tree tissue.

"And so there’s only a limited amount of time in Arizona where the psyllid can feed on the part of the citrus that it really likes," Wright said.

Wright will further study the effects of heat on citrus greening with colleagues at the University of California Davis and the University of Florida.

Even though the disease has yet to arrive in Arizona, commercial citrus growers defend their crop from the psyllid by spraying pesticides or growing trees under a protective screen. State officials also urge homeowners to obey citrus quarantines.

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