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2003
Table of Contents |
Introduction
Recently there has been increased interest in direct seeding crops in the dry land areas in the Pacific Northwest (PNW). Controlling annual and perennial weeds is difficult in direct seed systems, because it does not permit the use of tillage to control weeds during summer and winter fallow periods. Weed management in direct seed systems relies on the use of burndown herbicides during the fallow periods. Recently, growers have sometimes reported unsatisfactory grass control with glyphosate containing-products when used in chemical fallow. Ineffective weed control results in yield losses due to weed competition with the crop and moisture loss during fallow. Contamination of the harvested crop by weed seeds will reduce the grain quality and economic return of the harvested product. Ineffective weed control can cause disease carryover (greenbridge effect), which results in reduced yield and quality of the harvested product. Growers need improved information on glyphosate formulations, rates, application timing, and adjuvants to develop effective weed management programs for direct seed and chemical fallow systems.
Studies were conducted throughout the PNW in 2001 and 2002 to evaluate annual grass weed control with glyphosate-containing herbicides during fallow periods in direct seed, dry land winter wheat cropping systems.
Results and Interpretation
Trials were established in fields of standing wheat stubble near Davenport, Ralston, and Ritzville, Washington; Moro and Pendleton, Oregon; and Lewiston and Moscow, Idaho to evaluate weed control with glyphosate-containing herbicides during fallow periods in 2001 and 2002. The glyphosate products tested were Roundup Ultra, Roundup Original, Touchdown IQ, and Engame. Each product was applied at 0.281 lb ae/A (low), 0.375 lb ae/A (medium), and 0.562 lb ae/A (high) with and without 8.5 pounds ammonium sulfate (AMS) per 100 gallons of spray solution. Herbicide treatments were applied when the grasses were about six inches tall. Control was evaluated visually 7, 14, 21, and 28 days after treatment (DAT). Above ground biomass was collected from a 2.7ft2 area in each plot 28 DAT. Only visual weed control 14 DAT and biomass 28 DAT data are presented.
Data not shown for experiments near Moro, OR and Moscow, ID in 2001, there were no differences among treatments. Control ranged from 83 to 86% at Moro and was 100% at Moscow. In 2002, experiments near Lewiston and Moscow, ID there were no differences among treatments 14 and 28 DAT (data not shown). At Lewiston grass weed control was 100% 14 and 28 DAT. At Moscow grass weed control 14 DAT was 85% and biomass was reduced 89 to 100% 28 DAT. In experiments near Moro, OR and Ralston, WA there were no differences among treatments 28 DAT (data not shown). Control was 100% at Moro and ranged from 83 to 100% at Ralston.
In an experiment near Davenport in 2002, the herbicide by rate by ammonium sulfate interaction was significant for visual control 14 DAT and weed biomass 28 DAT (Table 1). All rates of Engame and Roundup Ultra and the high rate of Roundup Original and Touchdown IQ with and without AMS controlled annual grass weeds 100% 14 DAT. Low and medium rates of Roundup Original and Touchdown IQ with AMS controlled annual grass weeds 94 to 98%. Control was least (78 to 80%) when Roundup Original and Touchdown IQ were applied at the low rate without AMS. Biomass 28 DAT was reduced 100% by all treatments, except the low rate of Roundup Original without AMS (33%) and low and medium rates of Touchdown IQ without AMS (47 and 67%, respectively) (data not shown).
Near Pendleton in 2001, Engame with and without AMS and Roundup Ultra, Roundup Original and Touchdown IQ with AMS controlled wheat and downy brome 97 to 99% 14 DAT (Table 2). Biomass 28 DAT was reduced 98 to 100% by all treatments, except for Touchdown IQ without AMS (97%). Near Davenport in 2001, Engame and Roundup Ultra applied with and without AMS controlled annual grass weeds 96 to 98% 14 DAT. Roundup Original and Touchdown IQ applied with AMS controlled annual grass weeds 90 to 92%, and 86% when applied without AMS. In an experiment near Moro in 2002, Engame with and without AMS controlled downy brome 87 to 89%. Downy brome control with Roundup Ultra and Roundup Original with and without AMS and Touchdown IQ with AMS ranged from 79 to 83% and control was least (73%) with Touchdown IQ without AMS.
The AMS by herbicide rate interaction was significant at Pendleton 14 and 28 DAT and at Lewiston 28 DAT in 2001 (Table 3). Visual control 14 DAT was 97 to 99% at all herbicide rates with AMS and the high rate without AMS. Control was least (89 to 94%) with the low and medium herbicide rates without AMS. At Pendleton and Lewiston in 2001 28 DAT biomass was reduced 97 to 100% by all treatments, except for the low herbicide rate without AMS (93%) at Lewiston in 2001. In an experiment near Pendleton in 2002, the high herbicide rate with and without AMS reduced biomass 98 to 99%. Biomass was reduced 95 to 96% with the medium herbicide rate with and without AMS and the low herbicide rate with AMS. Biomass was reduced 92% at the low herbicide rate without AMS.
Near Davenport in 2001, all rates of Engame and Roundup Ultra and the high rate of Roundup Original and Touchdown IQ controlled annual grass weeds 94% or greater 14 DAT (Table 4). Biomass 28 DAT was reduced 96 to 100% by all rates of Engame and Roundup Ultra, and the high rate of Roundup Original and Touchdown IQ. The low and medium rates of Roundup Original controlled grass weeds 78 and 88% 14 DAT and reduced biomass 28 DAT 67 and 64%, respectively. The low and medium rates of Touchdown IQ controlled weeds 83 and 90% 14 DAT and reduced biomass 28 DAT 59 and 84%, respectively.
Herbicide main effect was significant 14 DAT in experiments near Ritzville and Lewiston in 2001 and Moro and Ralston in 2002 (Table 5). Near Ritzville, Engame and Roundup Ultra controlled annual grass weeds 93%, while Roundup Original and Touchdown IQ controlled weeds 85 and 90%, respectively. Near Lewiston, control of annual grass weeds was greatest with Engame (98%), while Roundup Ultra, Roundup Original, and Touchdown IQ control ranged from 92 to 94%. At Moro, Engame and Roundup Original controlled annual grass weeds 94 and 89%, while treatments with Touchdown IQ and Roundup Ultra controlled weeds 81 to 83%. At Ralston, control of annual grass weeds was 99% with Engame and 97% with Roundup Ultra and Touchdown IQ.
The herbicide rate effect was significant 14 DAT in experiments near Moro, Ritzville, and Lewiston in 2001 and Moro, Pendleton, and Ralston in 2002 (Table 6). At each location, control increased with increasing herbicide rate. In 2001, annual grass weed control ranged from 89 to 90, 88 to 93, and 91 to 97% at Moro, Ritzville, and Lewiston, respectively. In 2002, control ranged from 80 to 89, 73 to 75, and 97 to 99% at Moro, Pendleton, and Ralston, respectively.
The ammonium sulfate effect was significant in 2001 in experiments near Lewiston and Ritzville 14 DAT and Davenport 28 DAT (Table 7). Near Lewiston, treatments with AMS controlled annual grass weeds 96% and at Ritzville 88%, while treatments without AMS control was 92 and 84%, respectively. Near Davenport, treatments with AMS controlled grass weeds 92%, and without AMS control was 86%. In an experiment near Moro in 2002, all treatments with AMS controlled grass weeds 88%, while treatments without AMS controlled weeds 84% 14 DAT.
Final Conclusions
In 2001, Engame and Roundup Ultra at all rates and all locations consistently provided the greatest control of annual grass weeds. In 2002, Engame provided equal or greater control of annual grass weeds compared to Roundup Ultra and Roundup Original and was usually better than Touchdown IQ at all locations. In 2001 and 2002, the high and medium herbicide rates and the addition of AMS usually improved weed control compared to low herbicide rates and treatments without AMS.
 Contact
us: Hans Kok, (208)885-5971
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