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Preemergent Herbicides on Home Landscapes

by aseligmann — last modified Jul 24, 2010 12:00 AM

In order to achieve a perfect lawn, many people use 'preemergent' herbicides. These are applied before weeds come up in the spring and prevent weed development.

Granule Spreader (PD)

The top two preemergent herbicides used on home landscapes in 2001 were pendimethalin and DCPA. Both are classified by the U.S. Environmental Protection Agency as "possible human carcinogens" which means they might cause cancer in people. Both also have the potential to harm endangered species.

Pendimethalin

Animal studies show that pendimethalin causes one kind of thyroid tumor. When considering the risk of cancer in humans, the EPA is mostly concerned about people being exposed when they handle products that contain this chemical.

To reduce the cancer risk for workers, EPA increased the number of hours that they had to to stay out of treated areas; now workers can't re-enter an area for 24 hours (instead of 12 hours)

Homeowners, on the other hand, are instructed to stay off the lawn only until it's dry. Practically speaking, EPA can't require consumers to stay off the lawn. Instead of protecting families from any exposure, EPA decided that consumer products could be applied at 2 lbs/acre -- an amount lower than in products for commercial use.

EPA also recognized that pendimethalin might harm some endangered plants, birds, and fish - including endangered Pacific salmon.

NCAP filed a lawsuit against EPA that forced them to acknowledge that some chinook, steelhead and sockeye might need protection from exposure to pendimethalin. Four areas with potential problems were identified in Oregon, Washington and Idaho. The affected endangered salmon populations are found in the Willamette, Columbia and Snake rivers.

Pendimethalin is found in lawn products such as: Scotts Halts Crabgrass Preventer, Pre-M 0.86% Plus Fert, and Trugreen By Chemlawn Crabgrass Prevent+Lawn Fert22

DCPA

DCPA causes thyroid tumors in animal studies. In addition, hexachlorobenzene, a "probable human carcinogen" is an impurity found in DCPA.

To reduce that amount of DCPA that people might get from their diet, EPA has put some restrictions on its use. Livestock may not be fed hay, grass, crops, or other foliage that were treated with DCPA.

Drinking water can be contaminated with DCPA because of its use on turf (lawns). One site in Suffolk County, New York showed water contamination at levels that triggered concerns about the risk of humans getting cancer from drinking it. (The company that made DCPA decided to stop selling it in that county).

Regarding endangered species, the EPA has concerns that use of DCPA on turf could affect some mammals and mollusks (eg. clams).

DCPA is found in products that have 'Dacthal' in the product name.

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Resources:

U.S. EPA.2004. Pesticides industry sales and usage: 2000 and 2001 market estimates. http://www.epa.gov/oppbead1/pestsales/01pestsales/market_estimates2001.pdf. See pp. 14-15 (Tables 3.6 and 3.7)

U.S. EPA. 1998. R.E.D. facts: DCPA. http://www.epa.gov/oppsrrd1/REDs/factsheets/0270fact.pdf

U.S. EPA. 1997. R.E.D. facts: Pendimethalin. http://www.epa.gov/oppsrrd1/REDs/factsheets/0187fact.pdf