How Long After Using Roundup Can Pets Be in the Yard?

The Chemicals in Roundup

• The active ingredient in Roundup is a herbicide called glyphosate, which was discovered in 1970 by a researcher working for the Monsanto Company. After you spray gyphosate on a plant's leaves and the plant absorbs it, it spreads through the plant's phloem to areas of new growth. Once there, it interferes with an enzyme needed for growth, and the plant soon wilts and dies. Besides glyphosate, many Roundup products contain inert ingredients to help glyphosate interact with plant cells and enable faster absorption. Because they are inert, these ingredients aren't listed on the label.

Toxicity of Glyphosate

• The Extension Toxicology Network of Cornell University describes glyphosate as a "moderately toxic herbicide," going on to say that it would be considered relatively nontoxic except for the fact that it causes eye irritation. Tests with rats and dogs showed no short-term toxic effects, and those same tests concluded that glyphosate causes no reproductive damage and is not carcinogenic to animals. Animals digest glyphosate poorly and excrete most of it unchanged. In one experiment, rats were fed glyphosate every day for three weeks, and tests conducted 10 days after the feeding regimen concluded showed only minute amounts of the chemical in their tissues.

Glyphosate and POEA

• Glyphosate may be relatively nontoxic by itself, but study results suggest it may be more dangerous in combination with the inert ingredients in Roundup, especially polyethoxylated tallowamine (POEA). Researchers at the University of Caen found POEA more deadly to cells than glyphosate, and doctors in Japan confirmed that it was POEA that killed a number of people who drank Roundup in the 1980s. The combination can be lethal to some aquatic life. Researchers at the University of Pittsburgh found that adding Roundup to a pond containing frogs and tadpoles killed many of the tadpoles.

Pets and Roundup

• You should keep pets away from any area you've sprayed while the herbicide is wet. This is for the safety of the pets, but there's another good reason. Your dog or cat may track the herbicide through the lawn, and because the herbicide is nonselective, grass and other desirable plants in your garden may die. Once the herbicide dries on the leaves, it's safe to assume it has all been absorbed by the plants, and you can allow your pets back into the yard. This takes only a few hours.