Seeking hidden killers

Plague: After reports of plum pox virus in Pennsylvania, Maryland begins screening for the pathogen, which kills fruit trees.

July 26, 2000|By Anne Haddad | Anne Haddad,SUN STAFF

The plant detectives have been out since May, walking through commercial orchards and back yards, plucking leaves as potential evidence of a virus that spells death for stone-fruit trees.

Their quarry is the plum pox virus, which respects no borders and threatens to rob U.S. fruit growers of a $1.8 billion industry in peaches, nectarines, plums, apricots, cherries and almonds.

Testing in Maryland and at least 38 other states has so far yielded no sign of the virus, but it has been found just 25 miles away in Adams and Cumberland counties in central Pennsylvania.

"This would be the most scary of anything that's happened to me," said Robert Black, owner of Catoctin Mountain Orchard in Thurmont, Frederick County.

"A hailstorm can devastate a whole crop in 10 minutes, but you'll get a crop next year," Black said. "You can recover from other things, but this is different. It can take seven years to get back into production."

After dogging European growers for most of the 20th century, the virus made its first appearance in the United States last fall in Pennsylvania, forcing the destruction of nearly 1,000 acres of stone-fruit trees about 25 miles north of the Maryland border. The U.S. Department of Agriculture has set aside $13.2 million to compensate growers.

"It basically puts you out of the peach business," said Stephen Weber, owner of Weber's Cider Mill Farm in Cub Hill in eastern Baltimore County.

Once infected trees are removed and destroyed, the land has to remain cleared of stone-fruit trees for three years. It then takes three to five years before a tree starts producing enough fruit for a grower to make a profit.

Maryland growers earned $4 million from wholesale peach sales in 1999, according to the Maryland Agricultural Statistics Service.

A plant virus cannot infect humans, and the fruit of an infected tree is safe to eat, said Anne Bird Sindermann, plant pathologist at the Maryland Department of Agriculture. The effort to eradicate plum pox has top priority in Sindermann's plant-protection lab. The staff works four days a week on plum pox and one day a week on the other pests and diseases that bedevil crops.

The fruit of an infected tree is unappetizing, even if it is harmless, Sindermann said. The virus robs the fruit of sweetness and distorts it with rings, blemishes or bumps.

"It reduces sugar content, causes premature drop and distorts the fruit," Sindermann said. "So the fruit is essentially unmarketable."

Plum pox, also called Sharka, was discovered in Bulgaria in 1915. Sindermann said no one has been able to determine how plum pox made its way to Pennsylvania, but it was most likely spread through infected bud wood - twigs from one tree that are grafted onto a host tree for propagation. Once the virus is in a tree, it can be spread to other trees through aphids, small green insects.

Allan Baugher, owner of Baugher's Orchard in Westminster, said aphids usually don't fly long distances, but he's only about 25 miles from the quarantine area in Pennsylvania.

"I guess if you get a good strong wind, an aphid can fly down here pretty fast," Baugher said.

Nationally, the plum pox war comes second only to the battle to eradicate the citrus canker that has been menacing southern Florida, said Laurene Levy, a plant pathologist with the USDA who is the country's leading expert on plum pox and other exotic plant diseases.

If plum pox were to spread, its effect could be even worse than that of the citrus canker, on which the USDA is spending $171 million this year in a program to destroy infected and exposed trees.

"The size and scope of this is just mind-boggling," Levy said of the nation's stone-fruit trees, which grow in all 50 states.

Agriculture officials are tracking commercial orchards, but backyard infestations can be elusive. The best hope, Levy said, is for an education campaign to warn people to look for the disease. No one likes to have their cherished trees destroyed, but to leave them infected with plum pox could cause huge financial losses to farmers, she said.

In Maryland, the state testing program has cost about $180,000 so far this year and encompasses about 32,000 trees on 2,500 acres. At Baugher's, for example, every fourth tree is tagged with a bar code for continuous monitoring by Sindermann's staff.

Field workers - including extra summer help - started plucking 120,408 leaves in May that they've taken to the state agriculture lab in Annapolis.

A second round of testing will begin later in the fall. The high temperatures of late summer can often make the virus undetectable, Sindermann said, so the leaf collecting has stopped until September. However, field workers will be doing further checking for visual symptoms at orchards and in back yards. Even ornamental varieties of vulnerable trees, which don't bear fruit, can carry the disease.

Though plum pox was verified in the United States only last year, reports from growers lead Levy to believe the symptoms have been around for about three years - the growers just didn't recognize them.

And if the symptoms have been around for three years, Levy said, she is sure that the virus has been on these shores for at least three years before that.

"I'd say we're looking at three more years of vigilant surveying before we can say it's not around," Levy said. Public education is paramount, she said, both to watch for plum pox and to raise awareness of how plant diseases can be smuggled into the country.

"The best eyes are the growers, the master gardeners," she said. "Maryland is doing a lot more aggressive surveying [than other states], and they're smart to. They're in close proximity."

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