Voracious Grape Pest Now Suspect in Citrus Disease

Agricultural researchers have launched a four-year study to determine whether a voracious bug that has wreaked havoc on California’s wine industry could also be harming the state’s citrus groves.

Scientists with the California Citrus Research Board will soon begin scouring orchards in Ventura and Riverside counties for links between the glassy-winged sharpshooter and a host of emerging problems affecting fruit and trees.

The needle-nosed insect, which spreads a disease that has devastated Temecula Valley vineyards and poses a major threat to other grape-growing regions, has made its home in California’s citrus groves for more than a decade.

But other than causing trees to go thirsty--the yellow-eyed bug drains fluids as it feeds--it wasn’t thought to be an immediate danger until recently, when pest populations began to explode and fruit scarring and other problems began appearing in citrus groves.

Ted Batkin, president of the Visalia-based citrus board, said researchers will try to determine whether the bug is responsible for those problems and, if so, what growers can do to keep sharpshooter populations in check.

“We don’t know whether the kinds of problems we are seeing are caused by the sharpshooter or not,” Batkin said. “We just know we have a problem, and we’ve got to find the answer to it.”

More than 60 research projects are underway across California to battle the half-inch insect, an exotic pest accidentally brought into the state from Mexico and discovered in 1989.

Unlike other pests that feed on fruit, the sharpshooter does its damage by delivering a bacterium that causes Pierce’s disease, which clogs water-carrying vessels in plants--starving them of nutrients--and causing them to dry up.

To prevent the insect from moving into winemaking regions such as Napa and Sonoma, state regulators have invoked a range of restrictions on shipments of nursery stock and other agricultural products.

Although grapevines are particularly susceptible to Pierce’s disease, the bacterium does not have the same lethal effect on citrus trees. However, the bug has spread a related strain of the bacterium that has devastated citrus groves in Brazil and other South American countries.

At the very least, many growers are having to spend additional money to water trees that are being dehydrated by large numbers of the sucking insects, said Chris Taylor, senior vice president of farming for the Santa Paula-based Limoneira Co., Ventura County’s largest farming enterprise.

But Taylor said it’s possible that trees are being stressed by the sharpshooter to the point where they are producing smaller, low-quality fruit.

“If I could eradicate it I would, but I don’t think that’s ever going to happen,” Taylor said. “Our best hope is to try to control their numbers. But it’s pretty precocious. It doesn’t have too many enemies. It’s kind of near the top of the food chain for bugs.”