|Rainbolt, Curtis - UNIVERSITY OF IDAHO|
|Thill, Donald - UNIVERSITY OF IDAHO|
Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 28, 2004
Publication Date: May 1, 2004
Citation: Rainbolt,C.R., D.C Thill, and F.L. Young. 2004 Control of volunteer herbicide-resistant wheat and canola. Weed Technology. 18(3):711-718. Interpretive Summary: Crops resistant to glyphosate and other herbicides pose a potential problem for the Pacific Northwest (PNW) growers who rely on glyphosate for control of volunteer crops and weeds during fallow and prior to planting the next crop. Herbicides for the control of volunteer herbicide-resistant wheat and canola in PNW conservation tillage systems were evaluated during 2000 and 2001 near Ralston, WA and Moscow, ID. Glyphosate-resistant wheat was controlled > 90% with paraquat + diuron 14 days after treatment (DAT). In contrast treatments containing quizalofop-P or clethodim controlled glyphosate-resistant wheat 58 to 87% 14 DAT, but improved to > 90% 21 DAT. Imidazolinone-resistant wheat was controlled 95 to 99% with paraquat + diuron and 85 to 96% with all glyphosate treatments, except glyphosate-isoproylamine salt (IPA) + glufosinate (60 to 75%) and glyphosate-IPA + paraquat (50 to 66%) 14 DAT. Volunteer glyphosate-resistant canola was controlled 92 and 97% 14 DAT, and 76 and 98% 21 DAT with paraquat and paraquat + diuron, respectively. Imidazolinone- and glufosinate-resistant canola were controlled 84% or more with all treatments that contained glyphosate 14 DAT. By 21 DAT control of imidazolinone-resistant and glufosinate-resistant canola was 94 to 98% with paraquat + diuron and all glyphosate treatments, except glyphosate-IPA + glufosinate (88 to 93%) and glyphosate-IPA + paraquat (67 to 85%). In these studies, the best alternatives to glyphosate for the control of volunteer herbicide-resistant wheat were paraquat + diuron, clethodim, and quizalofop-P. The best alternative for controlling volunteer herbicide-resistant canola was paraquat + diuron.
Technical Abstract: Research on herbicide-resistant crops is beginning in the Pacific Northwest (PNW) with herbicide ' resistant wheat cultivars possibly being released in 5 or 6 years. It is expected that growers will embrace herbicide-resistant crop technology with great enthusiasm because it will allow them to effectively control some of their most troublesome weeds (jointed goatgrass, wild oat, and downy brome) in the growing crop. The down-side of this technology is the need to control the volunteer herbicide-resistant crop as a weed. Growers will need to be educated on the use of herbicide-resistant crops and how to control them when they become volunteer weeds. However there is presently no information on how to incorporate herbicide-resistant crops into PNW production systems. A 2-yr study was conducted at two locations to evaluate herbicides for the control of volunteer herbicide-resistant wheat and canola in no-till systems. Of major concern to the growers is the need for an inexpensive and effective herbicide to control glyphosate-resistant wheat and canola. The most rapid and effective herbicide to manage volunteer glyphosate-resistant wheat and canola was a combination of paraquat plus diuron. This effective herbicide combination would reduce the possibility of volunteer herbicide-resistant canola from hybridizing with weedy relatives and reduce gene-flow between canola cultivars with different resistant technologies. The herbicide combination applied pre-plant also rapidly kills volunteer herbicide-resistant wheat which greatly reduces the incidence of diseases in the subsequent crops.