The Status of Biological Control of Weeds with Fungal Pathogens

Weeds continue to cause major problems in agriculture throughout the world, reducing yield and quality of crops by competing for the water, nutrients, and sunlight essential for vigorous crop growth. The importance of weeds is reflected by the rapid growth of the use of chemical herbicides in agriculture throughout the world. The effectiveness of herbicides has dramatically in­ creased yields in many cases and, in turn, stimulated development of new chemical herbicides. However, despite massive efforts, weeds continue to cause significant losses. These losses result from the selection and emergence of species that are not controlled by currently available herbicides, the inability of a herbicide to selectively control certain weedy species without injury to crop species, or the development of resistant strains. Plant pathogens have been suggested as one of several possible means of controlling the weeds that remain problematic in otherwise successful weed control programs in intensive agriculture or even as an alternative to chemical herbicides. Plant pathogens, along with insects, are also being considered as a potential cost­ effective means of reducing weed populations in crops, forests, or rangelands where low profit margins preclude large herbicide expenditures. Biological control of weeds with plant pathogens has been the subject of numerous reviews and several books, and the reader is referred to these for additional information (13, 15, 73, 78). This review concentrates on selected