Utah Department of Agriculture officials said Friday the infestation of the gypsy moth in Salt Lake County covers more than 20 square miles and threatens hardwood, fruit trees, oakbrush and other plants.

Deputy Commissioner of Agriculture Edison Stephens said the infestation extends from the University of Utah south to Draper and includes the Hidden Cove area, Little Cottonwood Canyon, Big Cottonwood Canyon, other areas along the east bench and west into most residential areas of the county."It is too late this year to spray for the gypsy moth. We will start spraying and other eradication methods early next spring, as soon as the larva hatch and before they turn into moths," Stephens said.

"The larva stage is the harmful stage. That's when the gypsy moth attacks and destroys plants."

While a widespread infestation of gypsy moths could be disastrous to the state's fruit growers, Stephens said another problem could be caused in the state's watersheds if the oakbrush along the sides of hills overlooking reservoirs, rivers and streams is destroyed by the moths.

"This will cause untold erosion and could cost water districts millions of dollars to purify our culinary water systems."

Trapping the moths has worked in some areas of the country where the infestation has not been extensive, but so many gypsy moths have been sighted this summer and fall that trapping would not be feasible, Stephens said.

"Pesticides seem to be the answer in the Salt Lake County area. It seems to be the worst area for the gypsy moth in the state, although we are still making checks of traps from St. George to Cache County.

"We will used pesticides that are not toxic to humans and which will not hurt animals or bees."

Stephens said his department will ask the 1989 Legislature for an appropriation especially for the eradication of the gypsy moth.