New Ways to Put Peanut Weeds “Down Under”

By Jan Suszkiw

TIFTON, Ga., Dec. 16--Fierce competition among warring weeds forces many peanut growers to climb onto a herbicide treadmill.

But U.S. Department of Agriculture weed scientist Carroll Johnson has a new approach: Coax weed seedlings into the open early, when the pests are most vulnerable, and then rob them of sunlight.

Johnson's tests on small plots suggest peanut growers could save an estimated $12 per acre on weed-killing chemicals by using different farming practices.

"Currently, growers apply up to six different herbicides to keep pace with competing weed species," said Johnson, with USDA's Agricultural Research Service in Tifton, Ga. The weeds vie for sunlight, water and nutrients, all at the expense of the peanut crop--and the growers.

Peanut farmers in Southern coastal plain states such as Georgia, Alabama and Florida may spend $75 per acre applying herbicides to combat yellow nutsedge, Texas panicum, Florida beggarweed and other weeds, Johnson said.

And the herbicides aren’t a sure-fire defense. When one weed species is killed, another, more durable one may sprout in its place, Johnson noted. He's based at ARS' Nematodes, Weeds and Crops Research Unit in Tifton.

“What we're trying to do," he said, "is find the right combination of cultural practices to radically reduce herbicide use and cut other production costs. The critical weed-control period is the first 60 days of the crop's growth. If weeds are managed early on, fewer corrective measures are needed later."

About nine years ago, Johnson began combining different practices in an integrated approach. One promising tactic is the "stale seedbed." This means preparing a seedbed roughly 3 weeks before planting. Weed seeds soon germinate, but tilling the top 3 inches of soil shortly before planting time kills young weed seedlings before they can emerge.

When the crop is planted--in late April to mid-May--it's seeded in rows narrower than usual. Since the plants then grow closer together, this fosters a quicker leaf canopy that blocks sunlight from late-season weeds.

Peanut seed tops the farmer’s crop production costs. And Carroll credits today’s vacuum planter technology with enabling farmers to use the narrow rows without increasing peanut seeding rates. Early planter designs didn’t allow this.

Johnson conducted the small-scale studies last spring in cooperation with University of Georgia scientists Greg MacDonald, John Baldwin and John Beasley. The 18- by 20-foot experimental plots were infested with common coastal-plain weeds of peanuts: Florida beggarweed, yellow nutsedge, pitted morningglory and Florida pusley.

The next step, Johnson said, is to see if the results and projected savings hold up in tests on larger fields.

He plans to adapt the strategy to corn, cotton and cucurbits such as watermelon and cantaloupe, making life miserable for their weedy competitors as well.

Scientific contact: W. Carroll Johnson III, Nematodes, Weeds and Crops Research Unit, ARS, USDA, Tifton, Ga., phone (912) 386-3172, fax (912) 386-3437, cjohnson@tifton.cpes.peachnet.edu