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Managing Volunteer after Herbicide-Resistant Crops
Curtis Rainbolt, UI Weed Science Doctoral Student; Donn Thill, UI Weed Scientist; Dan Ball, OSU Weed Scientist, Pendleton, OR; Joe Yenish, WSU Extension Weed Scientist; and Frank Young, USDA-ARS Weed Scientist, Pullman, WA

ABSTRACT

Alternatives to Roundup were evaluated near Ralston, WA at the USDA Ralston Direct Seeding Project Site and near Moscow, ID at the University of Idaho Parker Research Farm in 2000. Volunteer Roundup Ready spring wheat was best controlled and its biomass reduced most by Gramoxone Extra + Direx, and treatments containing Select and Assure II. Clearfield wheat was controlled best with Touchdown, Assure II, Select, Gramoxone Extra + Direx, and all treatments containing Roundup Ultra RT. Roundup Ready canola was controlled best with Fallowmaster, Landmaster, and treatments containing Gramoxone Extra. Control of Clearfield and Liberty Link canola was greatest with Gramoxone Extra + Direx, Touchdown, and all treatments containing Roundup Ultra RT. Grass herbicides were applied at two growth stages and evaluated for control of volunteer Roundup Ready spring wheat at Genessee, ID, Pendleton, OR, and Pullman, WA. At Genessee, control of Roundup Ready spring wheat was 90% or more with all treatments containing Assure II, Select, or Poast applied at either timing, while at Pendelton and Pullman, control was better with these treatments applied at the 3 to 4 leaf growth stage, compared to those made at the 5 to 6 leaf stage.

INTRODUCTION

Farmers are readily adopting herbicide-resistant crops (HRC) into their crop production systems. Growers in Canada and the mid-western USA are planting millions of acres of farmland to herbicide-resistant canola, and corn and soybean, respectively. Herbicide-resistant wheat will be available soon to USA and Canadian farmers. They likely will adopt this new technology quickly and with the same enthusiasm as canola, corn, and soybean growers. Other new HRC will continue to be introduced during the next several years, which may result 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 Pacific Northwest (PNW) direct-seed, dry land winter wheat cropping systems. Important, unanswered questions include how best to control volunteer herbicide resistant crops in these situations. Traditionally, growers have relied on Roundup to control volunteer crops and weeds in no-till cropping systems. This poses a problem for control of volunteer herbicide resistant crops (HRC) such as Roundup Ready spring wheat and canola. Studies were conducted at several locations in the PNW to evaluate alternatives to traditional methods for control of volunteer Roundup Ready spring wheat and canola, Clearfield wheat and canola, and Liberty Link canola.

MATERIALS AND METHODS

Ralston, WA and Moscow, ID. Plots of Roundup Ready spring wheat and canola, Clearfield wheat and canola, and Liberty Link canola were planted into standing wheat stubble to simulate volunteer crops near Ralston, WA at the USDA Ralston Direct Seeding Project Site on April 31 and near Moscow, ID at the University of Idaho Parker Research Farm on May 8, 2000. Herbicide treatments were applied on May 15 at Ralston and on June 11 at Moscow. Control was evaluated visually at both locations 14 and 21 days after treatment (DAT). Herbicide treatments were Roundup Ultra RT, Landmaster BW, Fallowmaster, Gramoxone Extra, Rely, Touchdown, 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 in the Roundup Readyâ wheat and Clearfield wheat at Ralston and in all crops at Moscow 28 DAT. Canola biomass was not collected at Ralston due to inconsistent emergence and poor stand. Both studies were terminated immediately after biomass collection to prevent seed production.

Genessee, ID, Pendleton, OR, and Pullman, WA. Plots of 'Bobwhite' Roundup Ready spring wheat were seeded to simulate volunteer spring wheat in spring 2000 near Genessee, ID at the University of Idaho Kambitsch Research Farm on May 5, near Pendleton, OR at the Oregon State University Columbia Basin Agricultural Research Center on March 31, and near Pullman, WA on April 5. Treatments were Roundup Ultra at 0.56 lb/A, Assure II at 0.03, 0.046, and 0.061 lb/A, Roundup Ultra at 0.56 lb/A + Assure II at 0.03 lb/A, Roundup Ultra at 0.56 lb/A + Assure II at 0.046 lb/A, Roundup Ultra at 0.56 lb/A + Assure II at 0.061 lb/A, MON 78195 at 0.525, 0.788, and 1.05 lb/A, Selectâ at 0.109 lb/A, and Poastâ at 0.375 lb/A applied when the wheat was in the 3 to 4 and in the 5 to 6 leaf stages, and one untreated control (Table 2). Control was evaluated visually on June 21 and July 5 at Genessee, on May 30 and June 13 at Pendleton, and on June 19 at Pullman. All studies were terminated prior to spring wheat seed production.

RESULTS AND DISCUSSION

Ralston, WA. At Ralston, Roundup Ready wheat (RRW) biomass was reduced, compared to the untreated control, by all treatments except Roundup Ultra RT, Touchdown, Landmaster,and Fallowmaster (Table 3). The best treatments were Gramoxone Extra + Direx, Gramoxone Extra, Assure II, Select, Roundup Ultra RT + Select, and Roundup Ultra RT + Assure II, which reduced RRW biomass 92 to 96%. All herbicides reduced biomass of Clearfield wheat (CFW) compared to the untreated control; biomass of CFW was reduced 89% or more by all treatments except Rely (49% reduction). Volunteer crop control 14 days after treatment (DAT) (data not shown) was similar to 21 DAT (Table 4), with the exception of slightly higher control of RRW and CFW with treatments containing Gramoxone Extra 14 DAT. By 21 DAT, RRW control was best (89 to 96%) with Gramoxone Extra + Direx, and treatments containing Select or Assure II. CFW control was 88% or greater with all treatments except Rely (36%) and Gramoxone Extra (83%). Control of glyphosate-resistant canola (RRC) was best with Roundup Ultra RT + Gramoxone Extra (98%) and Gramoxone Extra + Direx (100%). Control of Clearfield canola (CFC) and Liberty Link canola (LLC) was 88% or better with Gramoxone Extra, Gramoxone Extra + Direx, Touchdown, and all treatments containing Roundup Ultra RT.

Moscow, ID. At Moscow, all treatments containing Rely, Gramoxone Extra, Assure II, and Select reduced RRW biomass compared to the untreated control (Table 5). Assure II and Select treatments reduced biomass most (86 to 92%). CFW biomass was reduced by all treatments compared to the untreated control. Biomass was reduced 87% or greater with all treatments containing Roundup Ultra RT, Touchdown, Assure II, or Select. RRC biomass was reduced by Gramoxone Extra + Direx (100%),Landmaster (96%), Fallowmaster (92%), Roundup Ultra RT + Gramoxone Extra (77%), Gramoxone Extra (76%), Rely (67%), and Roundup Ultra RT + Rely (61%),. CFC biomass was reduced 89% or more by all treatments except Assure II and Select. LLC biomass was reduced 82% or more by all treatments except Rely, Assure II, and Select. Volunteer crop control 14 DAT (data not shown) was similar to 21 DAT (Table 6), with the exception of slightly higher control of RRW and CFW with treatments containing Gramoxone Extra 14 DAT. By 21 DAT, RRW control was 91% or better with Assure II, Roundup Ultra RT + Assure II, Select, and Roundup Ultra RT + Select. CFW control was 89 to 100% with Select, Assure II, Touchdown, and all treatments containing Roundup Ultra RT except Roundup Ultra RT + Gramoxone Extra. RRC was controlled 96 to 100% with Gramoxone Extra + Direx, Landmaster, and Fallowmaster. Control of CFC and LLC was 93% or better with Gramoxone Extra + Direx, Touchdown, and all treatments containing Roundup Ultra RT except Roundup Ultra RT + Rely.

Genessee, ID, Pendleton, OR, and Pullman, WA. At Genessee on June 21, volunteer Roundup Ready wheat (RRW) control ranged from 83 to 97% for all treatments applied at the 3 to 4 leaf stage (Table 7), except Roundup Ultra RT alone (0% control). Control ranged from 30 to 44% for all treatments applied at the 5 to 6 leaf stage, with the exception of Roundup Ultra RT alone (0%). By July 5, all treatments, except Roundup Ultra RT alone, controlled RRW 90 to 99%. Control was best (97% or better) with Select or Poast applied at either timing.

At Pendleton on May 30, volunteer RRW control was 97% or better for all treatments applied at the 3 to 4 leaf stage, except Roundup Ultra RT applied alone (0% control). Control ranged from 63 to 85% for all treatments applied at the 5 to 6 leaf stage, with the exception of Roundup Ultra RT applied alone (0%). By June 13, RRW control ranged from 98 to 100% for all treatments applied at the 3 to 4 leaf stage and from 75 to 92% for all treatments applied at the 5 to 6 leaf stage, with the exception of Roundup Ultra RT applied at either timing (0%).

At Pullman on June 19, volunteer RRW control ranged from 90 to 95% for all treatments applied at the 3 to 4 leaf stage and from 70 to 88% for all treatments applied at the 5 to 6 leaf stage, with the exception of Roundup Ultra RT applied at at either timing (0%).