Cost-effective weed control in cereals: Part I. Competition, population dynamics and basic herbicide response studies; Part II. Field trials and seedbank studies

Abstract

Much new information was gained on the relative competitive abilities of a range of broad-leaved and grass weeds. Some of the factors leading to variation in response were studied and quantified for the first time. Our ability to predict the outcome of crop/weed competition is much improved as a result of this programme (although it is still relatively imprecise). The effects of crop density, relative time of emergence and soil nutrient level have been examined for a number of weed species. The phenology of growth of a number of weed species has been studied.

For the first time, seed production of some of our major broad-leaved species has been measured and related to total dry matter production. Behaviour of these seeds in the soil has been recorded, revealing some surprising differences in seed persistence between species. Simple models of long-term behaviour of these weeds have been derived; the first step quantifying the relationships between short-term and long-term economics of weed control. These specific studies have been supplemented by a study of soil seed bank populations from the long-term systems experiments described below.

The basic information gathered on herbicide efficacy and dose response relationships remains central to the adoption of herbicide programmes which are appropriate and not in excess of requirements, thus improving cost-effectiveness and reducing potential phytotoxicity.

The work on systems of weed control in practice has shown that the arbitrary thresholds used were conservative, erring on the side of 'spray' rather than 'no spray' decisions. However, because weed populations were usually above threshold levels, savings were modest and the work involved in assessing the weeds may not have been recouped by an economic benefit. In contrast, half doses of herbicide 'Insurance treatments' appear to have worked as well as full doses on almost all sites, giving maximum economic benefit for little sacrifice of yield or cost in management time.

The initial programme has been supplemented by further funding on Appropriate Rate Herbicides for Cereals and related reduced rate studies in Scotland. These are providing additional practical and basic information on specific weeds and herbicides to develop the cost effective strategies initiated in this programme. This initial programme can be seen to have contributed significantly to a new appreciation and awareness of cost-effective and environmentally friendly weed control within the farming community and the agrochemical industry.