Abstract:
The objective of this study was to determine the potential for integrating reduced herbicide
inputs with narrow row spacing to improve weed control in corn. Crops grown in narrow rows (row
spacings of 20 inches or less) shade weed seedlings more than those grown in traditional wide rows
(row spacings of 30 inches or more). Corn grown in narrow rows may require less herbicide than corn
grown in wide rows for equally effective weed control. Grain yields have been increased by as much
as 5 to 10% by switching from 30-inch to 20-inch and 15-inch row spacings. Reduced herbicide rates
in conjunction with narrow row corn production may have significant economic and environmental
benefits.
A field experiment was planted 12 May 1994 at the Farm Science Review site near London, Ohio. Treatments were arranged as a split-split plot in a randomized complete block design with three replications. Row widths were whole plots, plant populations were subplots, and herbicide treatments were sub-subplots. Two row widths (15 vs. 30-inch row spacings) and two seeding rates (24,000 vs. 30,000 plants/A) were used. Seven herbicide treatments were evaluated (Table 1). Labeled and reduced rates of a broadcast preemergence herbicide treatment (atrazine and metolachlor) and a postemergence herbicide treatment (nicosulfuron and dicamba) were compared to a control which received no herbicide inputs. Reduced herbicide rates were equivalent to 1/2 and 1/4 labeled rates.
Weed pressure was heavy throughout the experimental area. Giant foxtail and velvetleaf were the predominant weed species. Row width and plant population effects on weed control were either not significant (p=0.05) or not consistent on the different sampling dates. Any potential weed control provided by narrow rows and high plant population may have been limited by early season moisture stress which slowed vegetative growth and resulted in uneven canopy development. Lack of rainfall in late May and June also reduced the efficacy of the preemergence herbicide treatments (table 1). Above-ground weed dry matter (biomass) accumulation and visual ratings of weed control (for foxtail and velvetleaf) indicated that the postemergence herbicide treatments provided consistently better weed control compared to the preemergence herbicide. Above-ground weed biomass in the reduced rate preemergence herbicide treatment was not significantly different from the control; whereas in the reduced rate postemergence treatments it was less than 1/3 that of the control. Weed control provided by the reduced rates of the postemergence herbicides was not significantly different from that provided by the labeled rate. However, the weed control provided by the preemergence herbicides was significantly reduced at the 1/4 labeled rate.
Differences in grain yield were closely associated with the varying levels of weed control (Table 2). Yields, averaged over application rates, were greater for the postemergence herbicide treatments compared to the preemergence herbicide (123 vs. 86 bu/A). Reduced rates of postemergence herbicides did not significantly affect yield. Yields for the two reduced rate preemergence treatments were not significantly different from the control. The lower yields of the control and reduced rate preemergence herbicide treatments were associated with a greater percentage of barren plants and reduced plant stands. Row width did not influence yield, but the higher plant population, averaged across row width and the herbicide treatments increased yield (111 vs. 88 bu/A).
Extension Program Implementation
Results of this study will be reported at 1994 grower meetings, field days, and crop tours.
Data collected will also be summarized in the Ohio ICM Newsletter and Extension bulletins. Economic
evaluations will be performed on data to determine costs associated with different reduced herbicide
and control options. Additional research is needed before narrow row corn production can be
recommended by OSU Extension.
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