But there is no quick fix against devastating diseases

Jerry W. Jackson | Sentinel Staff Writer March 27, 2008

LAKE ALFRED - A natural form of aspirin and other compounds clobbers bacteria in crops and plants and fends off other diseases at the same time, offering at least some hope that citrus canker and citrus greening can be controlled, top Florida citrus scientists told growers Wednesday.

But the researchers with the University of Florida's Institute of Food and Agricultural Sciences in Polk County tried to dampen enthusiasm over any chances of a quick breakthrough, as the state's multibillion-dollar citrus industry battles potential devastation from the twin diseases.

Soil biologist Jim Graham said the technique known as SAR -- short for "systemic acquired resistance" -- has been shown to work in his own research, and in other trials, as a way of turning on a plant's own defense system. It offers another potential avenue of attack, in addition to regular pesticides, fertilizer and nutritional sprays.

Years of research remain, however, before scientists know which chemicals work best, how and when they should be applied and whether or not one serious and unintended consequence proves to be a threat. That unintended consequence: SAR may reduce levels of the bacteria that cause diseases such as greening to undetectable levels -- but not low enough to prevent them from being spread by insects.

"We don't want to create a Typhoid Mary situation," Graham said, referring to the phenomenon of a disease being spread unknowingly, leading to more infection and even greater losses.

Some growers are experimenting on their own with compounds such as salicylic acid, a naturally occurring plant hormone related to aspirin. But experts at the Citrus Research and Education Center meeting -- the first major gathering in Central Florida to discuss SAR -- said growers may do more harm than good.

Salicylic acid, for example, definitely plays a role in initiating a SAR response, Graham said, but it can damage plants and stunt their growth. Researchers said that one product labeled for use on citrus for "nutritional" purposes, with the brand name SAver, has 10 percent salicylic acid.

Whether SAver and other products now being tested for disease control -- such as Actigard, Serenade, Oxidate, K-phite and various fertilizers -- can be used alone or in various combinations safely and effectively is now the subject of intense study in Central Florida. Some of the more than 100 growers at Wednesday's meeting said they were encouraged by what they heard but remain cautious -- and worried.

"We need a lot more answers," said citrus grower Bert Harris, who has 165 acres of Valencia oranges in Highlands County.

He said he has his grove regularly inspected and follows the standard recommendation to push out and destroy any trees found to be infected with greening. Canker and greening are not harmful to humans but ruin the fruit and damage the trees.

Harris, 88, a former Florida state senator, said he is not trying any novel methods on his own, such as applying salicylic acid to try to ward off greening and canker. But he said that he and other growers are committed to financially backing research into SAR and other approaches in hopes that it will pay off "before we all have to get out of the business. Right now, we don't know if we're going to make it or not."

Gary Vallad, a former University of California-Davis scientist who studied SAR and its benefits for vegetables such as tomatoes before joining UF's faculty in June as an assistant professor of plant pathology, said the technique shows great promise but must be better understood to be truly effective.

"Plants are well defended," he said, and stimulating their complex defense systems with low doses of a pathogen or various chemicals is "an encouraging phenomenon" that "does not cure [but] retards the disease."

The researchers made it clear that they do not endorse any particular product, chemical or technique, and they fear growers will use "off-label" chemicals that will waste money and may do more harm than good, possibly even making their crop unmarketable.

Jerry W. Jackson can be reached at jwjackson@orlandosentinel.com or 407-420-5721.


Source:
http://www.orlandosentinel.com/news/space/orl-citrus2708mar27,0,242594.story