Dutch case studies showing the success and limitations of biological weed control

This paper analyses critical success factors for development of mycoherbici des by reference to two Dutch case studies. Chondronstereum purpureum, a pathogen of several hardwood species, attacks the introduced black cherry (Prunus serotina) which is a weed in Dutch fore sts. It is highly efficacious under diverse environmental conditions if myc elium fragments are applied to fresh wounds in the wood. The risk for non-t arget species was shown to be acceptable for most situations, and C. purpur eum is sold as a wood decay promotor in the Netherlands under the name Bioc hon. The market size is too limited to justify the costs of registration as a mycoherbicide. For Chenopodium album, the potential mycoherbicide market is much larger, t hose Chenopodium populations resistant to triazine herbicides alone being e conomic. Ascochyta caulina is a leaf and stem pathogen of Chenopodium and A triplex species. In maize and sugar beet, application of the fungus caused up to 70% mortality and considerable growth reduction of surviving Chenopod ium plants. Whilst encouraging, the results are too much dependent on weed growth stage and suitable weather conditions for practical use. Solutions a re being sought in fungus strain selection, formulation, and combinations o f the fungus with its own phytotoxins or a low dose of a herbicide in and E U-sponsored collaborative project.