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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.