EFFICACY OF REDUCED HERBICIDE DOSES IN SPRING CEREALS OF DIFFERENT COMPETITIVE ABILITY (REPRINTED FROM WEED-RESEARCH, VOL 32, PG 483-491, 1992)

The effect of dose reduction on the efficacy of MCPA/mecoprop and MCPA /fluroxypyr mixtures in the control of broad-leaved weeds was studied in spring barley (Hordeum vulgare L.) and spring wheat (Triticum aesti vum L.). Five crop densities were sown to obtain crop stands of differ ent competitive ability. Halving the highest recommended dose decrease d the control efficacy by 5-15 percentage units, but still provided a good weed control. Further reduction of the dose resulted in high vari ation in efficacy. The level of weed suppression was mainly determined by the competitiveness of the crop, environmental conditions and weed spectrum with differential sensitivity of species to the herbicides. No changes in the weed infestation were detected after continuous use of low herbicide doses for 3 years. The seed bank of weeds in soil was higher after a wheat-dominated rotation than after a barley-dominated rotation.