Citrus Crop in Valley at Risk for Diseases

By Melissa McEver, The Monitor, McAllen, Texas

Nov. 20–Adam Estrada doesn’t stay up nights worrying about diseases like citrus canker or greening. But if a tree infected with one of these diseases made its way to the Rio Grande Valley, he and other citrus growers could be up for many sleepless nights — and serious losses to their business.

“I haven’t really heard about it,” said Estrada, a La Feria citrus grower, of diseases like citrus canker. “It’s not here yet, and all we can do is prepare for it if it comes.”

Several diseases that have devastated Florida citrus groves in recent years could potentially reach the Valley, and in most cases, all it would take is someone illegally bringing in an afflicted tree.

Researchers at Texas A&M University-Kingsville’s Citrus Center in Weslaco are keeping a lookout for these diseases, as well as researching ways to protect the Valley’s trees from becoming infected.

Officials from the Texas Department of Agriculture say they also are stepping up enforcement of a quarantine prohibiting citrus trees from other states from entering Texas.

“There are a large number of diseases (in citrus trees) that are caused by viruses, and once they’re in a tree, there’s not much you can do,” said John da Graca, deputy director of the citrus center.

That’s why the experts are focusing on detection and prevention, da Graca said.

Some of the diseases of concern to researchers are citrus canker, a rapidly spreading bacterial disease that has destroyed about 10 percent of Florida’s commercial citrus groves; citrus greening, a disease spread by a pest already present in the Valley; the citrus tristeza virus, a plant killer transmitted through aphids and other pests; and a fungus that can kill trees rapidly.

All of these diseases either haven’t come to the Valley or have only limited impact so far, but it’s possible they could hurt Valley citrus in future years, said Mani Skaria, plant pathologist and professor at the citrus center.

“Some of these diseases could be very dangerous,” Skaria said.

Diseases like citrus canker or greening could be introduced to Texas in an unlikely place: East Texas backyards.

“A lot of people (in those areas) are interested in citrus trees and plant them in backyards for personal consumption,” Skaria said.

Some of those trees potentially could come from out of state and come bearing a lethal disease, he said.

To catch those diseases before they migrate to the Valley, the citrus center is conducting surveys and backyard-plant inspections in Beaumont, Port Arthur, Houston and nearby areas, Skaria said. So far, inspectors have found no sign of greening or citrus canker there.

Researchers also are taking soil and tree samples from the Valley to check for signs of disease here, Skaria said.

One pesky disease, the phytophthora fungus commonly known as “root rot” or the “plant destroyer,” has afflicted some Valley trees. The fungus is naturally present in the soil, but trees under attack by a pest called the citrus root weevil are much more vulnerable to the disease. A cluster of trees in McAllen has fallen prey to the weevil and therefore the fungus, and those trees are under quarantine to prevent further spread, Skaria said.

A widespread outbreak of root rot could cost the Texas citrus industry $15 billion, state officials have reported.

Ray Prewett, president of trade association Texas Citrus Mutual, said he’s less concerned about the “plant destroyer” fungus than he is about greening and citrus canker, which have impacted Florida’s citrus industry dramatically.

“We don’t have them, but there’s cause to be concerned,” Prewett said. “They could bring potentially major problems to our industry.”

Prewett would like to see an early detection program for those diseases in place, as well as more enforcement along the border of the quarantine.

“We need to step up efforts to keep out host plants,” he said.

David Kostroun, assistant commissioner for regulatory programs at Texas Department of Agriculture, said the agency is paying close attention to the dangers, working with the citrus center on monitoring tree conditions in the Valley, as well as inspecting trees at nurseries. With the assistance of the U.S. Department of Agriculture, Kostroun said the agency likely will expand its monitoring efforts.

Sometimes, agency representatives also conduct random road checks at Department of Public Safety weigh stations, Kostroun said.

Prewett suggested that TDA set up more road check stations along highways 281 and 77 — major thoroughfares to the Valley — as well as more stations in the Houston area to stave off the passage of rogue trees.

Even more than surveying or enforcement of the quarantine, arguably the best preventive measure against these diseases is the citrus center’s virus-free tree program. The program, which began in the early 1990s, offers tree cuttings that are certified free of any viruses. These “budwoods,” as growers call them, are grafted onto root stock and used for citrus tree propagation.

Most viruses spread through propagation, Skaria said.

“If you start with a healthy plant, chances are better that it will stay healthy,” he said.

The virus-free budwoods are for sale at the center in Weslaco, and so far the facility has sold more than half a million buds, da Graca said.

The Texas Legislature established the budwood program 10 years ago, and at the time gave TDA the option to mandate that all growers use virus-free budwood when propagating new trees. Kostroun said that once the citrus center has enough budwood of a certain variety, the agency will mandate virus-free budwood for that variety.

“The whole goal of the legislation is to eventually build a virus-free propagation (system),” he said.

Prewett hopes these efforts will keep the Valley’s citrus industry safe from crippling diseases — especially the diseases that can’t be treated. The best bet is to keep the diseases away from the Valley in the first place, he said.

“There’s no way to give these trees a vaccination,” Prewett said.

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