Exploiting diversity to manage weeds in agro-ecosystems

Abstract

Weed management systems that rely less on chemical control are needed globally. Next to curative chemical weed control, there are other ways of tackling weed problems, such as (a) reduction of the weed seed bank in the soil, (b) reduced recruitment of weed seeds from the soil seed bank, and (c) strengthening the relative competitive ability of the crop. A number of case studies are presented in which diversity is used as a basis for improved weed management. In the first case study, diversity refers to genetic variation within a crop species, which is utilized in breeding programmes aiming at the development of more competitive cultivars. In the other case studies, diversity refers to the reinforcement of weakly competitive crop species through the addition of a second species that contains a strong weedsuppressing function. Here a distinction is made between intercropping, where the species are grown simultaneously, and sequential or rotational cropping, where a cover crop is introduced in the cropping interval in between two main crops. Weed-competitive cultivars, intercropping and rotational cover cropping all have potential to contribute significantly to the weed management of agro-ecosystems. Rather than making curative control completely redundant, they allow the regular curative control measures to be applied at a lower dose or in a less frequent manner. The weed-suppressive effect was largely determined by the combined effects of genotype (or species) and management. Obtaining a sufficient level of weed suppression while maintaining the yielding ability is a major issue in the development of weed-competitive cultivars and the design of intercropping systems. In both cases, competition models showed to be useful tools to analyse and optimize systems. Opportunities and potential obstacles for implementation of the proposed strategies are discussed