Effects of soil type, weather and resistance on efficacy of herbicides against black-grass

Abstract

The aim of this project was to determine whether soil type, weather effects or genetic differences in resistance to herbicides could explain variability in response to herbicides.

Trays were filled with a standard volume of sandy loam soil from Anstey hall and seeded with either the local population or the standard susceptible Rothamsted black-grass (Alopecurus myosuroides) population. Trays of each population were sunk into field plots at each site and were over-sprayed with either chlorotoluron, isoproturon or fenoxaprop-ethyl.This experiment was repeated in 1992/93 and 1993/94 at each of six locations. The local black-grass population was tested for resistance using the standard glasshouse test but differences in activity in the field were not explained by the results of this test.

Adsortptive capacity of the soil was not a major factor influencing the activity of soil-acting herbicides at the levels recorded at these sites. It was concluded that weather factors had a major effect on the performance of herbicides for the control of black-grass with rainfall before and after spraying probably playing a major role.

The techniqe used proved difficult particularly in the wet autumn period in 1993. The trays were difficult to sink into the wet field soils in the autumn, particularly on the heavier soils.