The state Department of Agriculture has proposed using Dimilin, a synthetic pesticide, to kill off the invasive moth species that has ravaged oak trees around the state for decades.

“This breaks the ban on chemical spraying that’s been in place for 20 years,” said Jane Nogaki, of the New Jersey Environmental Federation.

Recent dry spring seasons prompted state officials to consider the chemical. During wetter seasons, a naturally occurring – but also nonnative – fungus typically flourishes and helps kill gypsy moths during their caterpillar stages. The fungus has faltered in recent seasons, leading to larger gypsy-moth populations that wiped out oaks throughout New Jersey.

The state has long sprayed the nonsynthetic Bacillus thuringiensis, or BT, but some believe it’s not as effective. BT remains active for only five days after it is sprayed, which has necessitated double doses. Dimilin remains active for 30 days.

That potency, combined with more staying power, is what concerns environmentalists. The state proposes maintaining buffer zones of at least 250 feet from waterways. A U.S. Geological Survey study in March, 2006, found that buffer zones did not fully limit pesticides.

About 20 environmental groups have signed a letter expressing their concern about the new pesticide, including the New Jersey Audubon Society, Citizens United to Protect the Maurice River, the New Jersey Sierra Club and various sportsmen’s clubs.