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How Combinations of Cultural Practices Aid Weed Control

Monday, March 1, 1999
filed under: Minimum Till/No-Till

USDA research in south central North Dakota and northeastern Colorado

underscores the synergism for sunflower weed control that occurs when

two or more helpful cultural practices are combined. While the main

reason(s) for employing practices such as narrow rows, higher plant

populations, delayed planting and cover cropping may not necessarily

relate directly to weed control, such practices can provide an important

assist in that regard, report Don Tanaka and Randy Anderson.

Tanaka is a soil scientist with the USDA-ARS Northern Great Plains

Research Laboratory at Mandan, N.D., while Anderson is director of the

Central Great Plains Research Station at Akron, Colo. Since 1995,

they've coordinated research into methods and technologies for the

development of high-residue production systems for dryland sunflower in

the Northern and High Plains. Along with that objective, the USDA

scientists have looked at how various cultural practices may likewise

aid with weed control. "Use of cultural practices to improve weed

control reduces producer input costs, potential for herbicide-resistant

weeds, and pesticide contamination of surface and ground waters," they

point out.

What have Tanaka and Anderson concluded? Based on their 1998 research

with weed control in no-till sunflower, and prior work conducted at both

Mandan and Akron during 1995-97, they note, not surprisingly, that

there's no "one size fits all" formula for cultural weed control across

the entire Great Plains. "Because of variations in climate and

precipitation patterns, cultural practices for effective weed control in

sunflower need to be developed by regions," they emphasize. As to

specific cultural practices, they conclude the following:

o Crop Canopy - Narrow rows (i.e., 15 to 18 inches apart) and higher

plant populations (i.e., 25 percent or more above normal populations)

help suppress weeds and also tend to increase subsequent seed yield -

regardless of location. That's due to the enhanced competitiveness of

the sunflower canopy when there are more plants in a given field and

those plants are closer together. Tanaka notes that narrow rows in the

Northern Plains commonly have resulted in yield increases of from 10 to

30 percent versus standard 30-inch rows; and, combined with higher

populations, also improve weed control.

o Delayed Planting - A delayed planting date can have a large impact on

weed control in the High Plains, but it's likely to have a limited or no

effect in the Northern Plains. The difference lies in the length of the

growing season - and planting window - in the respective regions.

"Because of the longer growing season, [this is] one of the most

effective practices to minimize weed growth" in the High Plains, say the

USDA researchers.

o Nitrogen Placement - Tanaka and Anderson say banding nitrogen near the

planted row contributes to reduced weed growth in the Northern Plains

growing region. That's because a broadcast application naturally will

"feed" between-row weeds as well as the sunflower. In the High Plains,

however, banding has a minimal effect on weed growth reduction because

the soils themselves are releasing quite high levels of nitrogen during

the warm June planting/early growth phase.

o Rye Cover Crop - Irrigated growers in the High Plains have been able

to make a rye cover crop work in their sunflower; but dryland producers

generally won't fare as well, suggest Tanaka and Anderson. That's

because "water is more limiting and rye can become a weed if winter

wheat is grown in the rotation" - which is usually the case in the High

Plains. For Northern Plains producers, a rye cover crop can effectively

reduce weed growth; but it also can contribute to moisture stress in the

sunflower crop, they add.

o Hybrid Choice - "Differences in growth habits of sunflower hybrids

[are] not sufficient to aid weed control" in the High Plains, the USDA

scientists state. In the Northern Plains, any effect one's choice of

hybrids may have on weed control is overshadowed by the need to choose

hybrids based on other essential considerations, such as yield and oil

content potential and disease tolerance.

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