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2003
Table of Contents |
Introduction
Weeds are a major problem in the development of successful direct-seed, conservation cropping systems. Problem weeds such as jointed goatgrass, feral rye, and downy brome are difficult or impossible to selectively control in wheat with current herbicide technologies. The development of herbicide-resistant wheat provides an opportunity to selectively control these and other weeds in direct-seed cropping systems. Herbicide-resistant wheat will soon be readily available to Pacific Northwest (PNW) wheat growers, and they likely will adopt this new technology quickly and with the same enthusiasm as canola, corn, and soybean growers. Additionally, other new herbicide resistant crops (HRC) will continue to be introduced during the next several years, potentially resulting in crop rotations containing mostly or all herbicide-resistant cultivars. However, there is little or no information on how to safely and effectively incorporate them into PNW direct-seed dry land cropping systems. Many of the herbicides used on HRC are currently used or are closely related to herbicides used extensively in direct seeding systems. Traditionally, growers have relied on glyphosate to control volunteer crops and weeds in no-till cropping systems. This poses a problem for control of volunteer HRC such as Roundup Ready (glyphosate-resistant) wheat and canola. Thus, it will be necessary to identify feasible alternatives to glyphosate for the control of volunteer herbicide-resistant crops.
Studies were conducted throughout the PNW between 1999 and 2002 to evaluate alternatives to glyphosate for control of volunteer glyphosate-resistant crops.
Results and Interpretation
Moscow, ID and Ralston, WA
Control of Volunteer Herbicide-Resistant Crops. Plots of Roundup Ready spring wheat and canola, Clearfield wheat and canola, and Liberty Link canola were planted at 20% of normal seeding rates (canola was seeded at 100% in 2001 due to poor emergence and stand counts the previous year) into standing wheat stubble to simulate volunteer crops near Ralston, WA at the USDA Ralston Direct Seeding Project Site and near Moscow, ID at the University of Idaho Parker Research Farm in spring 2000 and 2001. Herbicide treatments were applied when the wheat was in the 5 to 6 leaf stage and when the canola was 2 to 4 inches in diameter. Control was evaluated visually 14 and 21 days after treatment (DAT). Herbicide treatments were Roundup Ultra RT, Landmaster BW, Fallowmaster, Gramoxone Extra, Rely, Touchdown IQ, Roundup Ultra RT + Rely, Roundup Ultra RT + Gramoxone Extra, Gramoxone Extra + Direx, Assure II, Assure II + Roundup Ultra RT, Select, Select + Roundup Ultra RT, and an untreated control (Table 1). Above ground biomass was collected from a 2.7 ft2 area in each plot 28 DAT. Canola biomass was not collected at Ralston in 2000 due to inconsistent emergence and poor stand. Studies were terminated immediately after biomass collection to prevent seed production.
At 14 DAT, Roundup Ready wheat was controlled 93% by Gramoxone Extra + Direx (Table 2). By 21 DAT control was 90 to 95% with Gramoxone Extra + Direx and all treatments containing Assure II or Select. On average these treatments reduced biomass 95% compared to the untreated control. As expected, treatments containing only glyphosate did not control volunteer Roundup Ready wheat. Gramoxone Extra or Rely, alone or mixed with Roundup Ultra RT, also did not control volunteer Roundup Ready wheat.
Control of Clearfield wheat ranged from 89 to 97% with Roundup Ultra RT, Gramoxone Extra + Direx, Touchdown IQ, Landmaster BW, Fallowmaster, Assure II + Roundup Ultra RT, and Select + Roundup Ultra RT 14 DAT (Table 3). By 21 DAT Assure II, Select, and the previously listed treatments controlled volunteer Clearfield wheat 93 to 97 %. Biomass was reduced on average 96% by Roundup Ultra RT, Assure II, Assure II + Roundup Ultra RT, Select, Select + Roundup Ultra RT, Gramoxone Extra + Direx, Touchdown IQ, Landmaster BW, and Fallowmaster. Gramoxone or Rely alone or combined with Roundup Ultra RT did not control volunteer Clearfield wheat.
At 14 DAT, Roundup Ready canola was controlled 92% by Gramoxone Extra and 97% by Gramoxone Extra + Direx (Table 4). By 21 DAT, control had dropped slightly with Gramoxone Extra due to re-growth, but control with Gramoxone Extra + Direx was consistent at 98%. Biomass was reduced most by Gramoxone Extra + Direx, but due to a large degree of variation it was not significantly different than Roundup Ultra RT + Gramoxone, Gramoxone, and Landmaster BW. All other treatments did not control volunteer Roundup Ready Canola.
Control of Clearfield canola was 91% or greater with all treatments except Rely, Roundup Ultra RT + Rely, Assure II, and Select 14 DAT (Table 5). At 21 DAT, control was best with Roundup Ultra RT (96%), Landmaster BW (98%), Fallowmaster (98%), Touchdown IQ (94%), Gramoxone Extra + Direx (97%), Assure II + Roundup Ultra RT (96%), and Select + Roundup Ultra RT (95%). These treatments reduced biomass 96% on average. All other treatments did not control volunteer Clearfield Canola.
At 14 DAT, all treatments except Rely, Assure II, and Select controlled Liberty Link canola 92% or more (Table 6). By 21 DAT control was best with Roundup Ultra RT (95%), Landmaster BW (98%), Fallowmaster (98%), Touchdown IQ (95%), Roundup Ultra RT + Rely (93%), Gramoxone Extra + Direx (95%), Assure II + Roundup Ultra RT (97%), and Select + Roundup Ultra RT (96%). Roundup Ultra RT, Landmaster BW, Fallowmaster, Gramoxone Extra, Touchdown IQ, Roundup Ultra RT + Rely, Roundup Ultra RT + Gramoxone Extra, Gramoxone Extra + Direx, Assure II + Roundup Ultra RT, and Select + Roundup Ultra RT reduced biomass by 80% or more.
Clearfield wheat control with treatments containing glyphosate averaged 91% 14 DAT, compared to an average of 71% for Assure II and Select alone. By 21 DAT, control with Assure II and Select was 93 and 95% indicating that they can provide acceptable control levels, but are slower acting than glyphosate. Gramoxone Extra + Direx controlled all types of volunteer canola on average 98% 14 and 28 DAT. Control with Gramoxone Extra alone averaged 93% 14 DAT, but due to regrowth averaged 73% 28 DAT.
Genesee, ID
Control of Volunteer Roundup Ready Spring Wheat. Field trials were established at the University of Idaho Kambitsch Research Farm in spring 2000 and 2001 to evaluate several grass herbicides for control of volunteer Roundup Ready wheat. Roundup Ready ‘Bobwhite’ spring wheat was seeded with a double disk drill at a 20% of normal seeding rate to simulate volunteers. Plots were 8 by 30 ft arranged in a randomized complete block (RCB) design with four replications. All herbicide treatments were applied with a CO2 pressurized backpack sprayer calibrated to deliver 10 gpa at 32 psi and 3 mph. Control was evaluated visually 14 and 28 DAT. Studies were terminated prior to heading to prevent wheat seed production.
Control with all treatments applied at the 5 to 6 leaf stage, except Roundup Ultra RT alone (0% control), averaged 36% in 2000 compared to 72% in 2001 at 14 DAT (Table 7). This difference in control likely was due to climatic and growing conditions at the time of application. In 2001 applications were made during a period of light daily showers when the wheat was actively growing, possibly increasing the rate of herbicide absorption. Conditions were drier in 2000. By 28 DAT, control with all treatments, except Roundup Ultra alone, was 90% or greater both years.
The high level (90% or higher) of control achieved 14 DAT in 2001, are not typical compared to similar studies conducted (data not shown). In most situations Assure II, Poast, and Select require at minimum 21 to 28 DAT to achieve acceptable control levels.
Pendleton, OR
Control of Volunteer Winter Wheat in Fallow. A study was conducted at the Columbia Basin Agricultural Research Center to investigate control of volunteer common winter wheat in fallow. Plots were 6 by 30 ft in an RCB arrangement with four replications. Early-post emergence (EPOST) treatments were applied March 22, 2000 at the 5 to 6 leaf stage of volunteer wheat. Mid-post emergence (MPOST) treatments were applied April 19, 2000 at the 18 inch stage of volunteer wheat. All applications were made with a hand held CO2 sprayer delivering 10 gpa at 32 psi. Visual evaluations of volunteer wheat control were made April 10 and May 4, 2000.
EPOST treatments containing Roundup Ultra at 24 oz/A controlled volunteer winter wheat 100% 18 DAT, compared to 69 to 73% for Assure II alone, Select, or Poast (Table 8). By 42 DAT, control remained 100% with Roundup Ultra at 24 oz/A, but had increased to 92% on average for Assure II, Select, or Poast. Control with MPOST applications of Roundup Ultra alone or with Assure II controlled volunteer winter wheat 84 to 90% 14 DAT, while control ranged from 40 to 45% for Assure II alone, Select, or Poast.
All EPOST applications
provided acceptable control of volunteer winter wheat, but control was faster
with Roundup Ultra compared to the graminicides. MPOST applications containing
Roundup Ultra provided acceptable control 14 DAT, but because no later evaluations
were made it is unknown if Assure II alone, Select, or Poast would have reach
acceptable levels.
Control of Volunteer Roundup Ready Spring Wheat in 2000. A study was conducted
at the Columbia Basin Agricultural Research Center to investigate control of
volunteer herbicide-resistant spring wheat. The study was located in no-till,
Roundup Ready wheat stubble. Plots were 10 by 27 ft arranged in an RCB with
three replications. EPOST treatments were applied April 29, 2000 at the 3 to
4 leaf stage of volunteer wheat. MPOST treatments were applied May 12, 2000
at the 5 to 6 leaf stage of volunteer wheat. All applications were made with
a hand held CO2 sprayer delivering 10 gpa at 30 psi. Volunteer wheat control
was evaluated visually on May 30 and June 13, 2000.
On May 30, 2000 (30 DAT-EPOST and 18 DAT- MPOST) control with all treatments except for Roundup Ultra alone ranged from 97 to 99% for EPOST applications and 70 to 85% for MPOST applications (Table 9). By June 13 (30 DAT-MPOST), control with MPOST applications was 82 to 92%.
Earlier applications (3 to 4 leaf stage) of Assure II, Select, Poast, and MON 78195 controlled volunteer Roundup Ready wheat better than applications made at the 5-6 leaf stage.
Control of Overwintered Roundup Ready Spring Wheat in 2001. A study was conducted at the Columbia Basin Agricultural Research Center to investigate control of overwintered Roundup Ready spring wheat. Plots were 8 by 30 ft arranged in an RCB arrangement with four replications. EPOST treatments were applied March 23, 2001 on 5 to 6 leaf volunteer wheat. MPOST treatments were applied April 17, 2001 on 6 to 7 leaf volunteer wheat. All applications were made with a hand held CO2 sprayer delivering 10 gpa at 40 psi. Visual evaluations were made April 23, May 2 and June 18, 2001.
EPOST treatments controlled Roundup Ready spring wheat volunteers 71 to 80% on April 23 (31 DAT), and control improved to 93 to 98% by May 2 (Table 10). On June 18, control with Assure II at 3 oz/A + Roundup Ultra at 24 oz/A had decreased to 71%, while control remained 89% or higher with other EPOST treatments. Control with MPOST treatments except for Assure II at 3 oz/A + Roundup Ultra at 24 oz/A (51%) ranged from 65 to 71% on May 2 (14 DAT). On June 18, control with EPOST treatments tended to be best with higher rates of Assure II.
Applications made at the 5 to 6 leaf stage provided the best control, but required 40 DAT to reach acceptable levels.
Final conclusions
Assure II, other ACCase inhibiting herbicides, and Gramoxone Extra + Direx appear to be the most feasible alternatives to glyphosate for control of volunteer herbicide resistant wheat. However, no single herbicide or combination investigated has been as effective, consistent, or safe for use on subsequently planted crops as glyphosate. Control with alternatives is best with early application timings, but efficacy levels usually do not equal those obtained with glyphosate. Additionally, control with Assure II and other related herbicides usually requires about two weeks longer than glyphosate. Slower control could result in greenbridge problems from planting before volunteer crops and grass weeds are completely killed. Timing of greenbridge control in conjunction with planting is critical for control of Rhizoctonia root rot, other diseases, and insect pests in the PNW (Cook and Veseth 1991). Graminicides are also more sensitive than glyphosate to drought stress, which is a common environmental condition prior to planting. Another concern with ACCase inhibiting herbicides is that they are prone to the development of herbicide resistant biotypes (Lyon et al. 2002). Gramoxone Extra + Direx can provide rapid and effective control of volunteer wheat, but the soil residual properties of Direx have the potential to cause crop injury. Glyphosate costs about $4 to 6/ acre and is much more economical than Assure II, which costs approximately $8 to 12/acre and requires tank mixing with an additional herbicide for broadleaf weed control and Surefire, the commercially pre-mixed formulation of Gramoxone Extra + Direx, costs approximately $8 to 10/acre. Unless an adequate alternative to glyphosate is identified, tillage will be necessary following glyphosate-resistant crops to avoid yield losses from greenbridge problems, and tillage operations would reduce many of the benefits associated with direct seeding. It will be necessary for growers to decide if the ability to use glyphosate in a wheat crop is more beneficial than using glyphosate for control of volunteer wheat and weeds prior to planting and in fallow.
References
Cook, R. J. and R. J. Veseth. 1991. Wheat health management before planting. In Wheat Health Management. St. Paul, MN: American Phytopathological Society. pp. 87-104.
Lyon, D. J., A. J. Bussan, J. O. Evans, C. A. Mallory-Smith, and Thomas F. Peeper. 2002. Pest management implications of glyphosate-resistant wheat (Triticum aestivum) in the Western United States. Weed Tech. 16:680-690.
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us: Hans Kok, (208)885-5971
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