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More Corn Seed Can Mean Less Weed Seed

By Don Comis
November 6, 1997

Planting 50 percent more corn seed than usual cuts weed seed production by 69 to 94 percent, researchers say. Since fewer weeds grow, less chemical weed killer is needed for years to come, according to a 3-year study by the Agricultural Research Service in Beltsville, Md. The results also showed a significant increase in corn yields in some years.

The denser corn growth forms a tighter canopy that blocks off the sun from weeds such as velvetleaf. Trapped in the shade of taller corn plants, most weeds are prevented from maturing enough to produce seed.

ARS plant physiologist John R. Teasdale was most intrigued by the dropoff in numbers of seeds of velvetleaf, a major weed pest for corn growers. Computer projections show that having 80 percent less velvetleaf seeds could translate into a 12 percent higher annual farm profits. Plus, it would eliminate the need for herbicide in one of every four years, on average.

The ARS study compared yields of corn seeded at the typical rate--25,000 plants per acre--and at rates 50 and 100 percent higher.

Increasing the seeding rate can backfire, however, during a drought like the one that struck Maryland this past summer. Higher seeding rates mean more plants competing for the same amount of available moisture. In dry years, this can result in unacceptably low yields compared to fields planted at the typical rate. So, the researchers say, farmers may want to reserve the technique for irrigated fields or soils with good capacity for storing lots of moisture that corn roots can sip. They also advise against seeding at more than 50 percent above the typical rate.

Scientific contact: John R. Teasdale, USDA-ARS Weed Science Laboratory, Beltsville, MD, phone (301) 504-5504, fax 504-6491, e-mail