STEEP - Vegetation management with herbicides during fallow periods

2001 Table of Contents

2001 STEEP III Progress Report

RESEARCH PROJECT TITLE: Vegetation management with herbicides during fallow periods in direct seed, dry land winter wheat (Triticum aestivum) cropping systems in the Pacific Northwest.

Determine the effect of four glyphosate herbicide formulations, applied at several rates with and without ammonium sulfate on control of volunteer winter wheat and weeds during the fallow period in dry land, direct seed cropping systems in the Pacific Northwest.
Determine the effect of glyphosate and paraquat + diuron, applied sequentially during fall and/or spring at different rate combinations, on control of volunteer winter wheat and weeds during the fallow period in direct-seed, dry land winter wheat cropping systems.
Determine the cost effectiveness of fall and/or spring applications of burn down herbicides.
Disseminate information to growers and crop consultants via field tours, extension presentations and practical publications.

KEY WORDS: Ammonium sulfate (AMS), burn down herbicides, glyphosate

STATEMENT OF PROBLEM: 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 more difficult with this method of farming, 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 burn down herbicides during the fallow period. Recently, growers have 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 (green bridge effect), which also results in reduced 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.

ZONE OF INTEREST: High, intermediate, and low rainfall regions in dry land wheat productions areas in Idaho, Oregon, and Washington.

ABSTRACT OF RESEARCH FINDINGS: In spring 2001, trials were established near Davenport and Ritzville, Washington; Moro and Pendleton, Oregon; and Lewiston and Moscow, Idaho to evaluate control of grass weeds with glyphosate-containing herbicides during fallow periods. The glyphosate products tested were Roundup Ultra, Roundup Original, Touchdown IQ, and Engame. Each product was applied at 0.281, 0.375, and 0.562 lb ae/A with and without ammonium sulfate (AMS). Engame and Roundup Ultra at all rates and all locations consistently provided the best control of annual grass weeds. The addition of AMS usually improved weed control compared to treatments without AMS.

RESULTS AND INTERPRETATION: Trials were established in fields of standing wheat stubble near Davenport and Ritzville, Washington; Moro and Pendleton, Oregon; and Lewiston and Moscow, Idaho to evaluate weed control with glyphosate during fallow periods. 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. The experiment at each location was designed as spilt block with a factorial arrangement of treatments, except Lewiston, which was a split-split block with a factorial arrangement of treatments.

Near Moro, OR and Moscow, ID there were no differences among treatments. Control ranged from 83 to 86% at Moro and was 100% at Moscow.

Near Davenport, all rates of Engame and Roundup Ultra and the high rate of Roundup Original and Touchdown IQ controlled annual grass weeds 94% or greater14 DAT (Table 1). 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, respectively, and reduced biomass 28 DAT 65 to 68 percent. The low and medium rates of Touchdown IQ controlled weeds 83 to 90% 14 DAT and reduced biomass 28 DAT 59 and 84%, respectively. Engame and Roundup Ultra applied with and without AMS controlled annual grass weeds 96 to 98% 14 DAT (Table 2). Roundup Original and Touchdown IQ applied with AMS controlled annual grass weeds 90 to 92%, and 86% when applied without AMS.

Near Ritzville, low, medium, and high herbicide rates controlled grass weeds 88, 91 and 93%, respectively, 14 DAT (Table 3). The ammonium sulfate by herbicide rate interaction was significant for dry weight 28 DAT (Table 4). The low herbicide rates without AMS reduced biomass 94%, while all other treatments reduced biomass 99% or more.

Near Pendleton, Engame with and without AMS and Roundup Ultra, Roundup Original and Touchdown IQ with AMS controlled annual grass weeds 97 to 99% 14 DAT (Table 5). All treatments, except Touchdown IQ without AMS reduced weed biomass 99% or more 28 DAT. The ammonium sulfate by herbicide rate interaction was significant for visual control 14 DAT and weed biomass 28 DAT (Table 6). Visual control 14 DAT was 99% at the medium and high herbicide rates when mixed with AMS. Control was least (89 to 94%) when the low and medium herbicide rates were applied without AMS. Biomass 28 DAT was reduced most at the medium herbicide rate with AMS (100%) and least at the low rate without AMS (97%).

Near Lewiston, herbicides applied at medium and high rates controlled annual grass weeds 94 and 98%, respectively, 14 DAT (Table 7). Visual control 14 DAT was 99% with Engame and biomass was reduced 100% at 28 DAT (data not shown). Roundup Ultra, Roundup Original, and Touchdown IQ controlled annual grass weeds 93 to 94% and reduced biomass 97 to 100% 28 DAT (data not shown). All treatments with AMS control grass weeds 96%, while treatments without AMS 93% controlled weeds (data not shown).

INTERACTION (COOPERATION) WITH OTHER SCIENTIST CONDUCTING RELATED ACTIVITY: None.

PUBLICATIONS AND PRESENTATIONS: None.

Table 1. Visual control and dry weight of annual grass weeds with four glyphosate-containing herbicides at low, medium, and high application rates near Davenport, WA in 2001. Data are averaged over ammonium sulfate rates.

Table 1

Table 3

Table 4. Dry weight of annual grass weeds with glyphosate, with and without ammonium sulfate (AMS), at low, medium, and high application rates near Ritzville, WA in 2001. Data are averaged over glyphosate-containing herbicides.

Table 4

Table 5. Visual control and dry weight of annual grass weeds with four glyphosate containing herbicides with and without ammonium sulfate (AMS) near Pendleton, OR in 2001. Data are averaged over herbicide rates.

Table 5

Table 6. Visual control and dry weight of annual grass weeds with glyphosate with and without ammonium sulfate (AMS) at three herbicide rates near Pendleton, OR. in 2001. Data are averaged over glyphosate containing herbicides.

Table 6

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Hans Kok, WSU/UI Extension Conservation Tillage Specialist, UI Ag Science 231, PO Box 442339, Moscow, ID 83844 USA Redesigned by Leila Styer, CAHE Computer Resource Unit; Maintained by Debbie Marsh, Dept. of Crop & Soil Sciences, WSU