Effect of Water Quality on Post-emergence Grass Herbicide Efficacy

Date: October 1993
Term: 2 years
Status: Completed
Researchers: Rick Holm, University of Saskatchewan; Patrick McMullan, Agriculture and Agri-Food Canada
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a

Project Summary

Wild oats and green foxtail are two of the most troublesome annual weeds encountered by canola producers in western Canada. Several postemergence herbicides are available that will control these two weeds. Research was conducted in 1992 and 1993 at Brandon, Manitoba and Saskatoon, Saskatchewan to determine the effect of either alkali water or hard water on the efficacy of four postemergence grass herbicides, clethodim (Select), sethoxydim (Poast), fenoxaprop-p (Excel Super) and quizalofop (Assure). Overall, calcium sulphate did not reduce the efficacy of any of the herbicides. However, sodium bicarbonate did reduce the efficacy of sethoxydim and clethodim.

Wild oats and green foxtail are two of the most troublesome annual weeds encountered by canola producers in western Canada. Several postemergence herbicides are available that will control these two weeds. Herbicides must be applied in a carrier, such as water, to ensure distribution onto plant surfaces. The water quality can have an impact on herbicide efficacy. Water that is high in sodium and bicarbonates is termed ‘alkali’ water, while water that contains calcium and magnesium salts is considered ‘hard’ water.

Research was conducted in 1992 and 1993 at Brandon, Manitoba and Saskatoon, Saskatchewan to determine the effect of either alkali water or hard water on the efficacy of four postemergence grass herbicides, clethodim (Select), sethoxydim (Poast), fenoxaprop-p (Excel Super) and quizalofop (Assure). Tame oats were seeded at right angles to the canola crop to simulate wild oats.

Herbicides were applied at either the full recommended rate or one-half the label rate. Three rates of either sodium bicarbonate or calcium/magnesium sulphate were applied to the plots at 0, 250 or 500 ppm. An untreated check was included for each herbicide. Plots were visually evaluated approximately three weeks after herbicide application and grain yield measured after harvest.

In general, weed control was better at Saskatoon than at Brandon when no salts were present in the spray solution. Canola yields at Brandon were somewhat variable due to severe lodging and subsequent harvest difficulties. At Saskatoon, yield data generally reflected tame oats control, showing highest yields where tame oats control was highest. (Table 3 and Table 6)

Overall the project showed that fenoxaprop-p and quizalofop were not antagonized by either sodium bicarbonate or calcium sulphate in the water used for herbicide application. However, sodium bicarbonate reduced the efficacy of sethoxydim and clethodim. There appeared to be a relationship between herbicide rate and the sodium bicarbonate concentration in the water. Under conditions of stress, such as heat, drought or later growth stages of weeds at the time of herbicide application, sodium bicarbonate antagonism will be greater. Calcium sulphate did not reduce the efficacy of these two herbicides; in fact, at Saskatoon, clethodim efficacy appeared to improve with increasing calcium sulphate concentration.

Scientific Publications

F.A. Holm, J.L. Henry, D.W. Gruber and P. McMullan, 1995. Water Quality Effects on Phenoxy and ACCase Inhibiting Herbicides. Western Canada Agronomy Workshop, Red Deer, AB. July 5-7, 1995. (p 240-248). (Poster).

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