Colored Mulch Starves Nematodes
Red plastic mulch causes plants to put more of their energy into upper growth,
thus improving yields and, in the case of tomatoes, depriving nematodes of some
of their below-ground food.
Red plastic mulch is making life miserable for root knot nematodes in South
Carolina tomato fields.
In springtime field tests at Florence, tomato plants grown with red plastic
mulch were able to ward off the nematodes and produce more tomatoes than plants
grown with black plastic mulch, say U.S. Department of Agriculture plant
physiologist Michael J. Kasperbauer and Clemson University nematologist Bruce
For a decade, Kasperbauer and Patrick G. Hunt of USDA's
Agricultural Research Service have been
experimenting with colored mulches as a way to boost plant yields, while
conserving water and controlling weeds. They found that red mulch boosts yields
by increasing a tomato plant's ability to keep more of its growth above ground,
especially in the fruit. But the latest study is the first documenting that red
mulch also suppresses damage by nematodes that live in the roots.
"This is especially timely because of the impending ban on methyl
bromide, which is used to treat the soil to kill nematodes," says Hunt. He
and Kasperbauer are based at the agency's
Coastal Plains Soil, Water, and
Plant Research Laboratory in Florence.
The scientists are not certain how the red mulch helps tomato plants fight
off nematodes. But Kasperbauer says it could be due to a tug-of-war between the
mulch and the nematodes.
"The red mulch reflects wavelengths of light that cause the plant to
keep more growth above ground, which results in greater yield," he says.
"Meanwhile, the plant is putting less energy into its root system the very
food the nematodes feed on. So reflection from the red mulch, in effect, tugs
food away from the nematodes that are trying to draw nutrients from the
roots," says Kasperbauer.
To test the effects of colored mulches in small-scale field plots, the
research team sterilized the soil to eliminate all nematodes. Then they planted
the tomatoes, mulched them with black or red plastic, and inoculated the roots
with different numbers of nematodes ranging from 0 to 200,000 nematode eggs per
The results were dramatic, especially in spring. Plants inoculated with
200,000 nematode eggs and grown with black plastic mulch produced only 8 pounds
of tomatoes, compared to 17 pounds for the plants grown over red mulch.
Farmers and home gardeners who want to take advantage of the red mulch can
buy it commercially. ARS has filed a patent on the mulch and is working
cooperatively with Sonoco Products, Inc., of Hartsville, South Carolina, to
develop improved plastic mulches.
Ken-Bar, Inc., of Reading, Massachusetts, sells the mulch directly and
through several supply stores and catalogs. By Sean Adams,
ARS Information Staff.
Plains Soil, Water, and Plant Research Laboratory, 2611 West Lucas St.,
Florence, SC 29501-1242; phone (843) 669-5203