Two-gene Clearfield Wheat Varieties Show Improved Resistance to Beyond Herbicide
Sep 28, 2009
Clearfield wheat technology has been available for several years. It has generally helped producers gain improved control of feral rye, downy brome, jointed goatgrass, and other hard-to-control grasses, especially in continuous wheat or wheat-fallow systems. Control of feral rye and downy brome has at times been inconsistent, however, especially with spring applications. And occasionally, the Beyond herbicide has injured the Clearfield wheat varieties where spray applications have overlapped or where methylated seed oil (MSO) has been used as an adjuvant.
The first generation of Clearfield wheat varieties, such as Protection and Above, all contained a single gene for tolerance to Beyond herbicide. Recently, efforts have been made to develop a new generation of Clearfield wheat varieties with two genes for herbicide tolerance. The goal has been to gain improved tolerance to Beyond herbicide, and possibly be able to apply a higher rate of the herbicide with MSO as an adjuvant to achieve more consistent control of problem grasses, even with spring applications. Producers would like to be able to make spring applications if possible because that gives them more time to assess the yield potential of the wheat.
Tests at K-State have shown that the new 2-gene Clearfield wheat variety from AgriPro, AP503 CL2, does in fact have improved tolerance to Beyond herbicide. In two years of tests near Manhattan, none of the herbicide treatments injured the 2-gene Clearfield wheat, even at a 12-oz (2X) rate of Beyond plus MSO.
The introduction of 2-gene Clearfield wheat varieties has some potential advantages for problem grass control in the future. In our tests, the consistency of downy brome and feral rye control has been improved when Beyond is applied at higher rates and with MSO, even when applied in spring. Unfortunately, the current Beyond label is limited to a maximum use rate of 6 oz/acre. A supplemental label does, however, allow the use of MSO as an adjuvant with Beyond on 2-gene Clearfield varieties.
Labeling may be adjusted in the future as 2-gene Clearfield wheat varieties become more available. Cheat, Japanese brome, and jointed goatgrass control is normally acceptable at the 4 to 6 oz rate and with nonionic surfactant instead of MSO.
The 2-gene Clearfield
wheat provides an excellent level of crop safety with Beyond treatments, and thus may allow for expanded application rate and adjuvant options for enhanced weed control in the future.
Source: Kansas State University Extension Agronomy