In recent months, the college has organized and implemented a large educational program on plum pox virus, a devastating disease of stone fruit.

These peaches show the distinctive lesions of plum pox virus, an incurable disease that affects stone fruit, including plums, peaches, nectarines, and apricots.

In September 1999, fruit trees in several Adams County orchards were found to be infected with the incurable disease, which had never been seen in North America before.

Plant pathologists and horti-culturists from the U.S. Department of Agriculture's Animal and Plant Health Inspection Service (APHIS), the Pennsylvania Department of Agriculture's Bureau of Plant Industry, and the College of Agricultural Sciences have organized a cooperative program to control and possibly eradicate the virus.

Plum pox has infected Pennsylvania orchards for at least three years, according to Herbert Cole, professor of agricultural sciences. Growers noticed signs of disease in 1997 and sent fruit samples for tests when symptoms worsened the next year. In 1999, growers took samples to a meeting at Rutgers University, where a peach expert who had worked in Europe recognized the signs of plum pox. By October 1999, USDA and the Pennsylvania Department of Agriculture had positively identified plum pox virus as the cause of the problem.

The disease, also known as sharka (Slavic for "pox"), was first discovered in Bulgaria in 1915. Since then, it has slowly spread across Europe, where some 100 million trees have been infected. It also is found in Chile, where it was identified in 1994, and parts of Africa. It affects stone fruit, including peaches, plums, nectarines, and apricots. Some strains of the disease can affect cherry trees.

Plum pox virus, also known as sharka, had not been found in North America before th 1999 discovery of the disease in several Adams County orchards. At first glance, foliage symptoms can look like nutritional deficiencies or insect injury.

"Penn State's primary mission will be to educate fruit growers and related industries about management of the virus," Cole says. "Penn State and the state and federal departments of agriculture are focused on solving a very difficult problem."

The college launched a comprehensive Web site (http://sharka.cas.psu.edu) in December. Penn State and the state department of agriculture also sponsored a symposium on plum pox, bringing in several European specialists to recommend control strategies.

In January, Penn State experts presented a special forum on plum pox at the Mid-Atlantic Fruit and Vegetable Conference and developed an eight-page publication with the latest information about the disease. Both the publication and videotapes featuring highlights of the symposium will be available at Penn State Cooperative Extension county offices.

"Extension agents and specialists will conduct meetings for different grower groups over the winter," adds James Travis, professor of plant pathology. "We are working very hard to see that growers have up-to-date information. The publication is designed to be updated every few months, and the Web site will be updated regularly."

In Pennsylvania, the disease will affect primarily peach trees. In 1998, growers in the state produced 65 million pounds of peaches, worth $20.6 million. The state ranks fifth in peach production nationwide.

Sharka symptoms range from minor to severe. Foliage symptoms at first glance can look like a nutritional deficiency or insect injury. As the disease progresses, lesions can spread to the fruit, making it unsalable. Finally, the disease causes massive drops in yield, ranging from 80 to 100 percent.

"Research on plum pox will be coming in the future, but right now education is our focus," says John Halbrendt, associate professor of plant pathology at Penn State's Fruit Research and Extension Center in Biglerville. "The Biglerville facility also will be equipped to test samples taken from fruit trees in Pennsylvania for plum pox virus."

Tim Gottwald, a USDA statistician, estimates that when spring foliage appears at least 50,000 samples from trees in Adams and surrounding counties must be tested to determine if the virus has spread beyond the initial infected trees.

"By testing so many trees, we should be able to identify and eliminate infected trees," Halbrendt. "This will result in reducing the level of infection down to zero in a year or two. However, sampling will have to be continued for at least five years beyond that, and the Biglerville lab is a logical place to set up a testing facility."

--John Wall