The efficiency of bracken control using foliage-applied translocated herbicides depends upon the accumulation of a potentially lethal concentration of the active ingredient at the sites of action, the rhizome buds. There is evidence that the level of herbicide accumulation at these target sites is determined by a number of factors including the efficiency of cuticle penetration, absorption, translocation, metabolism and activity at the enzyme target sites. The level of metabolic activity of the rhizome/frond buds may be critical, dormant buds possibly receiving a sublethal dose. These buds may later become active and act as foci for reinfestation.

The nature of these problems is discussed with particular reference to studies carried out on the mode of action of [14C]asulam.

Work done by the authors in relation to bracken control is reviewed. These studies are largely concerned with the use of additives to enhance both the uptake and translocation of aminotriazole and asulam using a number of approaches: (a) estimating uptake by applying known herbicide concentrations in the presence of additives followed by washing off and residue determination after set times; (b) bioassay studies for selecting additives which can reduce herbicide scorching and therefore possibly enhance translocation; (c) field trials with selected formulations.

The chemical, physical and biological properties of asulam make this herbicide well suited for the selective control of bracken in various situations. These properties are reviewed and conditions considered to optimise the control of bracken and minimise the effect on the environment on both a short- and long-term basis.

The role of surfactants and mineral oils is considered.

South-west and west Scotland contains a large proportion of the bracken-infested hill pasture in that country and considerable effort has been expended over the past five decades on a scientific approach to bracken control. The trials of various, more or less successful, herbicides culminated in the current work based on the use of asulam or glyphosate which will control, but only in rare cases eradicate, bracken. Current work is aimed at improving the control effect by investigating and refining timing, rate and method of application, additives and mixtures. Particular emphasis is placed on techniques of improving the underlying sward, where present, and of investigating the factors influencing its growth. Experimental work has not shown any degree of allelopathy towards sown-in grass and clover seed growth, but depth of bracken litter is shown to be important. Doubt is expressed regarding the requirement for a total programme of bracken control and follow-up fertiliser treatment in all cases before grant aid is approved

Bracken is not a major weed problem on hill land in the north of Scotland, being restricted by environmental factors to the lower slopes of sheltered glens. There is no evidence of widespread stock poisoning by bracken in the area.

Ploughing and reclamation, forestry planting and spraying with the selective herbicide asulam have considerably reduced infestations of bracken on land worthy of improvement. At the present time there is little scope for further economic control of bracken.

Field experiments have defined full frond emergence from mid July to mid August as the most effective time for application of asulam. Reinfestation in about five years has been shown to follow incomplete control on small plots but an area sprayed by helicopter in 1972, where a very high degree of initial control was achieved, remained almost free of bracken in 1980.

Easier handling of stock and increased availability of summer grazing are reported following bracken control. An increase in herbage production has been measured experimentally in the second year after removal of the bracken by spraying.

‘Life can only be understood backwards but it must be lived forwards’.Thirty years of professional but spasmodic interest in the problem of bracken on the Scottish hills brings home the aptness of Kierkegaard's aphorism. Despite rapid technological change —from a man with a scythe to the pilot with a helicopter—the fact remains that control of this serious weed problem is currently running at only a fraction of the rate in the early fifties. Clearly, financial factors have played a major part in this situation but it is facile to lay the blame wholly at the door of economics. The objective of the paper is to summarise the dominant technical and economic aspects which have impinged upon the problem over three decades and to attempt to draw broad conclusions as to why we are in this situation and to outline more fruitful possibilities for the future.