Vegetative Mulch Cuts Pesticide Losses in
By Sarah Tarshis
August 25, 1999
Growing vegetables with an organic mulch, hairy vetch--a legume--instead of
plastic mulch cut pesticide losses by as much as 90 percent in experiments in
Maryland. The vetch also greatly reduced water runoff and sediment losses.
Today, Agricultural Research Service
scientists presented the findings--the first showing the tactic's effect on
pesticide loss--at a meeting of the American
Chemical Society in New Orleans. ARS is the USDA's chief scientific wing.
The Chesapeake Bay and its aquatic organisms have long been threatened by
polluted runoff from farms, lawns, golf courses, streets, septic tanks and
other sources. And on the Bay's Delmarva peninsula, runoff from vegetable
fields may contribute to endangering shellfish such as shrimp, clams and
oysters. The new findings point to ways to reduce this threat.
Polyethylene mulch is used to conserve soil moisture and control weeds on
about 4,600 acres of tomato and floral crops in Northhampton and Accomack
counties, Virginia, that make up Virginias eastern shore. Runoff
increases, however, because plastic covers 50 to 75 percent of the fields.
Pesticides that aren't absorbed into the soil can be removed easily from the
plastic surface by rain.
In a three-year collaborative study, ARS chemist Cathleen Hapeman and her
co-workers grew tomato plants in both plastic-covered and hairy vetch mulch
plots at the agency's Beltsville, Md.,
Agricultural Research Center. They measured the runoff and its sediment and
pesticide concentrations. Compared to the plastic-covered plots, the
vetch-mulch plots lost about two to 10 times less water, 10 times less soil and
on average, ten times less pesticide.
Scientists tested some runoff from the plots on clams and other
bottom-feeding organisms that serve as indicators of water quality. Preliminary
results of the tests, conducted at the University of Maryland's
Chesapeake Biological Laboratory in
Solomons, Md., showed that runoff from polyethylene plots can harm the aquatic
organisms. The organisms were less affected by runoff from plots mulched with
Scientific contact: Cathleen Hapeman, ARS
Laboratory, Beltsville, Md., phone (301) 504-6511, fax (301) 504-5048,