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PNW CONSERVATION TILLAGE HANDBOOK SERIES
Chapter 5 - Weed Control, No. 2, December-January 1985


Herbicide Effectiveness Under Conservation Tillage

Roger Veseth

Weed control is one of many management concerns when changing from a conventional tillage system to notill or minimum tillage. Are herbicides as effective in the higher residue conditions of no-till and minimum tillage? To address this concern, STEEP researchers Dorm Thin, University of Idaho weed scientist, and Don Morishita, weed scientific aide, established a research trial in the spring of 1983. Postemergence broadleaf herbicides were applied to winter wheat planted under three different tillages systems. The trial was near Potlatch, ID, in an annual cropping rotation following spring peas.

The three tillage systems were: conventional tillage, seeded with a John Deere, double-disk drill; minimum tillage with the "Chisel Planter" designed by University of Idaho agricultural engineers; and no-till with a Yielder notill drill. Fertilizer rate, planting date and seeding rate were identical in all tillage treatments.

In late March and early April, 11 postemergence broad leaf herbicide treatments were applied at the optimum crop stage and weed stage. Results showed no significant differences in crop injury, control of individual broadleaf weed species or grain yield between the three tillage systems for each herbicide treatment.

The research trial was repeated south of Lewiston, ID, in the spring of 1984. At this location, however, winter wheat was planted into small grain stubble instead of spring pea. No significant tillage-herbicide interactions were observed, the same conclusion as in the 1983 trial.

These results indicate that with the same target broad leaf weeds, no changes in postemergence broadleaf herbicide use or selection maybe necessary when changing from conventional tillage to no-till or minimum tillage. The researchers stress, however, that spray penetration of the residue and crop canopy is critical for weed herbicide contact and effective control. With standing cereal stubble or high residue levels, some adjustments in nozzle selection and angle, pressure, ground speed and other factors may be needed to achieve optimum herbicide coverage.

     
 

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