PORTLAND – After winning an agreement from Cherryfield Foods Inc. to stop aerial spraying of blueberry fields, four environmental groups are turning their attention to another blueberry processor, Jasper Wyman & Sons.

The Sierra Club, Environment Maine and two other groups put Wyman on notice Thursday that they intend to sue for alleged violations of the Clean Water Act. Wyman is based in Milbridge with a processing plant in Cherryfield.

Vivian Newman from the Sierra Club’s state chapter said Wyman officials told representatives of the environmental groups at a November meeting that there’s no reason to change its practices because the company follows the letter of the law.

But she said there is no monitoring of water quality and that a lawsuit would compel Wyman to release more data about its spraying program.

“Wyman should follow the lead of Cherryfield Foods to stop aerial spraying,” Matthew Davis of Environment Maine said in a statement. “Wyman has left us no choice but to start the process of filing a Clean Water Act lawsuit.”

James Kilbreth, a Portland attorney representing Wyman, said the company follows EPA regulations and is doing nothing wrong. He said a lawsuit would pose a threat not just to Wyman, but to any agricultural enterprise with pesticide spraying.

“This is a huge threat to agriculture in the state of Maine,” Kilbreth said.

Last October, Cherryfield Foods agreed to stop aerial spraying even though it, too, felt there was nothing wrong with its past practices. It now plans to apply pesticides with a boom sprayer instead of using aircraft this summer.

Like Cherryfield, Wyman contends it has followed EPA guidelines and filed an appropriate drift management plan with the state pesticide control board.

But Newman contends that pesticides drift into nearby rivers when sprayed on blueberry fields. She said the problem is exacerbated when aircraft have to deliver pesticides from a higher altitude because of tall trees next to blueberry fields.

Rivers that potentially could become contaminated include the Pleasant and Narraguagus, where wild Atlantic salmon were declared endangered in 2000, she said.