For most of the last 30 years, scientists and engineers have waged a war on the Eurasian watermilfoil, a non-indigenous water weed that diminishes swimming, boating and the environment. Using standard mechanical means of harvesting the milfoil, winning the war looked bleak. But, environmentally friendly biological control may be the answer, according to a Cornell University scientist.

"This weed is the zebra mussel of the plant world," said Bernd Blossey, director of the Biological Control of Non- Indigenous Plant Species Program at Cornell. "Almost every state has this problem. It is replacing the native macrophytes and has detrimental effects on the ecology of infested waters."

Using lessons learned from the war against another weed, purple loosestrife, Blossey, Robert Johnson, manager of the Cornell Experimental Ponds, and Nelson Hairston, Cornell professor of ecology and systematics, want to wage biological control against the milfoil. Blossey presented his report, "Biological Control of Weeds in Natural Areas," at the Cornell Biocontrol Conference, April 12, in Ithaca, N.Y.

Through research performed in Ithaca and by studying the effects of natural insect enemies of the purple loosestrife, Blossey believes there may be a scientific, biological template for controlling this type of water weed.

Meanwhile, harvesting the weeds seems to make the problems worse, Blossey said. Whenever a weed like purple loosestrife or the watermilfoil is mechanically harvested, the plant's natural enemies have no food to survive -- at least until it grows back. Within a few months the problem is just as bad as before or worse.

There is hope of controlling milfoil around the country. Blossey suggests just being patient. Simply allow the host- specific, natural entomological enemies to do their job, Blossey said.

In the case of the ornamentally beautiful purple loosestrife, there is a long list of natural enemies: the root-mining weevil, Hylobius transversovittatus, attacks the main storage tissue of the purple loosestrife; two leaf beetles, Galerucella calmariensis and G. pusilla, can completely defoliate individual plants and entire purple loosestrife populations; the weevil Nanophyes marmoratus feeds on the flowers; the weevil N. brevis feeds on the seeds.

All of them attack nothing but their host purple loosestrife, Blossey said.

The watermilfoil is but one weed in thousands. In New York, for example, there are more than 1,400 non-native plants grown. Blossey said that recreational lake users may be inadvertently contributing to the problem. For example, as small boat motors run across the lake, the propellers could churn the milfoil, allowing it to take root elsewhere in the lake, and boaters could easily transfer it to other water bodies inadvertently.

Scientists cringe at the thought of using chemical herbicides on such underwater weeds. And chemicals provide only varying degrees of success. Biological control seems to be the most appealing method of tackling the problem.

The search for biological control continues. "Biological methods are not always readily available," Blossey said. "Nor have those methods always been well-endorsed or financially supported. Despite an excellent safety record, skepticism concerning the safety and effectiveness of exotic insect introductions for weed control remains high among the general public, administrators -- and even scientists."