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Chemical weed control under stubble mulching

R.J. Batemanand and S.R. Walker

Queensland Department of Primary Industries, Kingaroy Qld. 4610.

The pre-emergent herbicides, Trifluralin, Pendimethalin and Vernolate, are widely used in the South Burnett to control annual grasses in peanuts. It is recommended that they be incorporated into a stubble free seedbed prior to sowing. This practice is inconsistent with the need to protect these soils against erosion with a stubble mulch.

Weed control was assessed following herbicide application to stubble mulched seedbeds in 1977 and 1978. in order to determine the effect of stubble cover on herbicide effectiveness. The three herbicides were applied at recommended rates, and incorporated immediately by a sweep cultivator with attached self rotating rod weeder. Weed control was rated against untreated plots (rating 5 representing 100% control). and the results for day 50 are presented in Figure 1.

Surface cover (%)

Figure 1. Relationship between herbicide effectiveness and stubble cover for three herbicides.

Quadratic regression analysis showed a significant relationship between herbicide effectiveness and stubble cover, with effectiveness generally decreasing with increasing stubble levels. If 90% control (4.5 rating) is taken as a satisfactory level of control, the critical stubble cover level for the three herbicides investigated were:


28% cover


23% cover


21% cover

Although these levels are relatively low, rainfall simulaton studies in the U.S. have shown great reductions in soil loss at similar stubble levels. (Lattanzi et al. 1974)

These results indicate that a stubble free seedbed is not a pre-requisite for effective chemical weed control in peanut cultivation.

Lattanzt, A.R., Meyer,R.J., and Baumgardner, M.F. (1974). Soil Sci.Soc.Amer.Proc. 38:946.

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