Herbicides, pesticides and other lawn chemicals pose little threat to ground water or local streams if applied correctly, but too many homeowners ignore the directions and their actions can create environmental hazards, according to two recent studies by a University of Maryland agronomy professor.

During a media tour last Thursday at the university's Cooperative Extension Service's turf farm, a 35-acre facility where more than 100 varieties of grass are studied, agronomists, soil microbiologists and environmentalists gathered to discuss the results of experiments that examined lawn chemicals' effect on water quality.

The studies, funded by the university and the federal and state departments of agriculture, were initiated because environmentalists have long blamed lawn chemical runoff as a major pollutant in Washington area creeks and streams and a key problem in the decline of the Chesapeake Bay, according to the scientists.

J. Scott Angle, who directed the two studies, said the harm comes from misuse of lawn fertilizers and could be virtually eliminated once homeowners and gardners are educated about the use of chemicals.

His studies were carried out on grass plots at the Chesapeake Bay Foundation's Claggett Farms in Upper Marlboro. After three years of applying fertilizers and other chemicals to the plots in the same manner and amount as commercial lawn care companies and using a machine to simulate rainstorms, Angle found that the runoff that occurred was so insignificant as to prove harmless to ground water or the bay. But when twice the amount of chemicals was used, as he said often happens on residential lawns, the excess simply ran off the soil.

"The problem is many homeowners do not follow the guidelines," Angle said. "They say, 'If I apply a certain amount of fertilizers to my lawn and it looks this good, then I'll apply twice as much and it will look twice as good.' But the lawn can only assimilate so much and the excess has to go somewhere; most of the time it's the Chesapeake Bay."

Michael Heller, who farms and lives on Claggett's 285 acres and is a member of the Chesapeake Bay Foundation, agreed that much of the chemicals' deadly journey into the water supply results from misapplication, but cautioned against oversimplifying the problem. He noted that once the chemicals reach the ground water "there's no remedy, we can't go back and clean it up."

"There's still a gray area in terms of information," he said. "Many of the pesticides used on lawns have not been well studied."

"There's nothing wrong with green lawns. A properly fertilized lawn is a healthy lawn and will do a better job at protecting the environment by discouraging soil erosion," Heller said. "But people can overdo it."

Angle also noted that some types of operations, especially golf courses, can create special problems because they receive large amounts of pesticides and fertilizers and are mowed very close to the ground.

Although suburban lawns may seem a long way from the Chesapeake Bay, the chemicals applied can find their way into the water system. Every time it rains, water runs off freshly fertilized lawns, carrying potentially hazardous chemicals into tributaries to the bay or drinking water reservoirs. Or the chemicals can seep deep into the soil with the rain, entering the ground water.

Scientists at the turf farm stressed that educating people dealing with lawn care to use fertilizers properly will help alleviate an environmental threat quicker than the mystery surrounding lawn chemicals can be unraveled.

Guidelines released each May by University of Maryland's Agronomy Department advise homeowners to keep grass mowed to between 2 1/2 to 3 inches high, which reduces weeds and the need for herbicides.

State agronomists recommend growing tall fescues and zoysia grass for the fewest pest problems.

"When grass is properly managed, the potential environmental harm is minimal," said Angle, who added that following the university's guidelines could reduce the need for chemicals by 50 percent to 75 percent.