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Field Trial Indicates Weeds Not Affected Much by Wheat Seeding Rate, Row Spacing A field trial at the West Central Research and Outreach Center at Morris, Minn., was conducted last year to determine the effect of seeding rate and row spacing of wheat on weed population. The objective of the study—funded in part through the Minnesota wheat checkoff, managed by the Minnesota Wheat Research and Promotion Council—was to see if broadleaf herbicide use can be reduced or eliminated. Wheat was seeded at three rates: Ninety lbs/ac (1.26 million seeds), 120 lbs/ac (1.680 million seeds), and 150 lbs/ac (2.1 million seeds). At each seeding rate, wheat was seeded in conventional 7.50” rows and in narrow 3.75” rows, with and without post-emergence broadleaf weed control. The study site was field cultivated, fertilizer broadcast 98-46-60 (N-P2O5-K2O), and field cultivated a second time for fertilizer incorporation and seedbed preparation on May 2, 2001, when Russ wheat was seeded. Broadleaf weed counts were taken at the 2-leaf, 5-leaf, and pre-harvest stages of wheat. At the pre-harvest stage of wheat, weeds were not counted unless they were greater than 4 inches in height. Bronate at 1 pt/ac + Stinger at 1/3 pt/ac were applied post-emergence at the 5-leaf stage of wheat, after taking 5-leaf stage weed counts, for broadleaf weed control to selected treatments. Results from the trial indicated that seeding rate and row spacing had no significant influence on weed populations in wheat. Weed populations at the 5-leaf stage of wheat, just prior to herbicide application in selected treatments are given in Table 1, as are weed populations at pre-harvest both with and without broadleaf herbicide application. Weed populations decreased both with and without broadleaf herbicide application from the 5-leaf stage (May 31) to just prior to harvest (July 27). Natural competition from the wheat smothered out weeds from 5-leaf to pre-harvest. Weed pressure at 5-leaf and pre-harvest appears to be greater at the 90 lb seeding rate than at the 120 and 150 lb seeding rates, but this is not a significant difference. There was no difference in weed pressure in narrow verses conventional row widths and no difference in grain yield. Weeds present were approximately 80% redroot pigweed, 15% common lambsquarter, and 5% other. “With lower plant populations, we just got more tillering, which reduced any possible benefits of greater wheat to weed competition through increased plant uniformity with narrow rows or planting at higher populations,” says George Nelson, WROC research scientist. Several years ago, Nelson looked at whether narrower rows and a higher seeding rate would result in a more uniform wheat heading, which would be more beneficial for spraying wheat at anthesis for FHB (scab) suppression. He found that a higher seeding rate resulted in a slight yield advantage, but had no significant effect on the timing or duration of the wheat heading period.
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