DENVER (AP) — Garden-care giant Ortho said Tuesday it will stop using a class of chemicals widely believed to harm bees.

The company plans to phase out neonicotinoids by 2021 in eight products used to control garden pests and diseases.

Ortho will change three products for roses, flowers, trees and shrubs by 2017 and other products later, said Tim Martin, vice president and general manager of Ortho, a division of Marysville, Ohio-based Scotts Miracle-Gro Co.

The chemicals, called neonics for short, attack the central nervous systems of insects. Some advocates say neonics are one of several reasons behind declining populations of bees, which are major pollinators of food crops.

About one-third of the human diet comes from insect-pollinated plants, and honeybees are responsible for 80 percent of that pollination.

Ortho is acting out of concern for possible threats to honeybees and other pollinators and to reassure customers that "Ortho's got their back, taking care of whatever they need controlled in the most responsible manner," Martin said.

The change might require gardeners to apply the reformulated products more frequently, but it will be easier to target pests while reducing the chances of hurting bees, he said. The cost of the products won't change significantly, Martin said.

It wasn't immediately clear what effect Ortho's decision would have on the health of the overall bee population. Neonics are used in a number of chemicals applied to food and textile crops such as corn and cotton as well as individual gardens.

The severity of the effects of neonics on bees appears to vary depending on what type of crops or plants they are used on, according to a study by the U.S. Environmental Protection Agency and California's environmental agency that was released in January. Another study published last year showed neonics might hit wild bumblebees harder than domestically raised honeybees.

Bayer CropScience and Syngenta, the top manufacturers of neonics, have said the research has exaggerated the risks and understated the benefits.

Concern about bee health is growing. Last week, the Maryland General Assembly passed a bill that would allow only certified applicators, farmers and veterinarians to apply pesticides containing neonics. In March, the U.S. Fish and Wildlife Service said it would consider whether to protect two species of wild bumblebees under the Endangered Species Act amid declines in their numbers.

The environmental group Defenders of Wildlife, which asked the service to consider protecting the bees, said neonics were one a factor in the bees' decline.