By Sharon OmahenUniversity of GeorgiaBobby Scott Jr. had two choices. He could yank up his grape vinesor watch as Pierce’s disease ate through his earnings.He chose option three.When the Aiken, S.C., wine grape grower called University ofGeorgia professor C.J. Chang, he needed hope, help and answers.”Pierce’s disease is the major limiting factor for the success ofthe wine industry in the southern United States,” Chang said. Plant-derived controlUndeterred, Chang set out to find a plant-derived compound forcontrol. His answer came in a product called terpene, developedby the Eden Research of Oxfordshire, U.K.Scott is allowing Chang to test these potential control methodsin his vineyard. More than 500 test-plot wine grapes are now partof Scott’s 20 acres of wine grapes.The terpene solution is being fed to the grapevines through thevineyard’s drip irrigation system. Comparing the treatment tountreated control vines, the grower is seeing dramatic results.The treated vines are thriving while the untreated are sufferingthe effects of the disease.Chang is now working to develop a strategy to put in place incase wine-grape growers in north Georgia begin to see diseasesymptoms. Time is on the side of Georgia growers as the diseasespreads slowly at higher elevations.”The disease spreads slowly in vineyards that are 1,600 to 1,800feet or more above sea level,” Chang said. “There are someresistant muscadine and American wild grape hybrids available,but relying on these flavors alone limits marketability forSouthern growers.”As Chang and Scott work to develop ways to fight Pierce’s diseasein grapes, growers wait.”Until we can control it, our county agents are recommending thatgrowers yank out the diseased vines,” Chang said. “It soundsharsh, but right now it’s the most effective control around.” Replace or importWithin two to four years of contracting the disease, most grapevines originating from Europe die, he said. To fight the disease,wine grape growers must either replant vines periodically toreplace the diseased vines or import grapes from other regions tokeep their businesses going.Since the early 1980s, Chang has been searching for a way tocontrol Xylella fastidiosa. The bacterium is associated withthree major crop diseases in Georgia: Pierce’s disease of grapes,phony peach disease and plum leaf scald.When Scott contacted Chang, he was running out of options. Noplant pathologists in South Carolina were studying Pierce’sdisease. He turned to Chang in desperation.Since that first phone call, the two have developed a partnershipin the fight against Xylella fastidiosa. Scott has beencrossbreeding European grape varieties with bunch grape-muscadinehybrids resistant to Xylella fastidiosa. To date, he’s bredthousands of young seedlings. Oddly enough, he needed Chang toinoculate the fledgling vines with the bacterium. Breeding for resistance”I start in the greenhouse with the new crosses,” Scott said. “Then they have to be inoculated so we can see how many survive.”Scott then plants the new potentially-tolerant vines in thefield. Many of his crosses don’t survive to live outside thegreenhouse and many die in the field. “We lose a lot of crosses along the way, but I know eventuallywe’re gonna be successful,” he said. “I feel good about theprogress we’re making. But it’s taking a little longer than Ihad hoped.”Scott now has 3,000 Pierce’s disease-tolerant vines in hisfamily’s Montmorenci Vineyard. Vineifier grapes are used tointroduce good quality wine genes.”We both acknowledge that as long as we work hard, the fruit ofour labor will be tolerant wine grapes for the Southern region,”Chang said.Besides breeding disease-tolerant grape varieties, UGAresearchers have been searching for other ways to control thebacterium. In 1979, scientists found it can be slowed down bytetracycline treatments. The find turned out to be a breakthroughin controlling diseases caused by Xylella fastidiosa.Tetracycline successfully suppressed the symptoms of plum leafscald disease and oak leaf scorch. But researchers hit a snagwhen it came to using it on food-bearing crops.”Unfortunately, EPA frowned on the use of tetracycline as acontrol method,” Chang said. “They were concerned over theenvironmental hazards, and they think it could produce a bugthat’s resistant to tetracycline. So we can use it on trees likeoaks and sycamores, but not on food crops.”
Landscape planting season is upon us and home gardeners may be eager to buy new fruit trees and ornamentals. New plant material is often produced bare root — without soil — and must be either kept in cold storage or temporarily planted outdoors to survive.If bare root plants cannot be planted immediately, then certain precautions must be taken to ensure their survival. Home landscapers must make sure bare root plants don’t dry out or freeze before they are planted in their permanent spot. Don’t store bare root plants in a bucket of water. This cuts off all essential oxygen to the roots. If refrigerated storage is available, store the bare root plants there. First, make sure the roots are in good, moist condition before storage. Next, return the roots to the moistened packing material the plant was shipped in and place the plant into refrigerated storage. Don’t store plants with fruits and vegetables, as produce can give off gases that can harm new plants. Maintain the storage temperature between 38 and 45 degrees.If you can’t plant immediately and cold storage isn’t available, the best alternative is to plant in a pot or temporarily plant by covering the root with moist soil or mulch. This temporary planting is called ‘heeling in.’Select a shady, well-drained site in the landscape. Avoid northern and northwestern exposures as most cold fronts come from these directions.Dig a shallow trench wide enough to accommodate the plant’s root systems. For multiple plants, separate them, spread them out and cover them with moist soil. Keep varieties labeled and separate.Water roots thoroughly and be sure all roots in contact with moist soil. This completes the heeling process.When you are ready to move the new plant to its permanent home in your landscape, be careful not to damage the roots.