chapter  22
34 Pages

Biological Approaches to Weed Management

ByDennis L. Isaacson, Raghavan Charudattan

Even though biological control of weeds is practiced in many countries, there are relatively few professional workers in the field, and there is not a well-developed body of literature. Much of the work published on biological weed control is found in journals from related fields, such as plant ecology, weed science, range management, entomology, or plant pathology. Although these sources can be located easily and searched, there are several literature sources that may be difficult to find and are not included in some abstracts of biology and agriculture. Some of the most important of these sources are listed in Table 1.

Pathogens may be applied in an inundative or augmentative strategy as bioherbicides. The technique of controlling weeds with planned applications of large doses of a pathogen is regarded as the microbial herbicide strategy (also called inundative control strategy or the bioherbicide strategy). A significant level of research activity is currently underway in several countries to discover, develop, and use plant pathogens as biological control agents of weeds in both classic and inundative weed control programs (Table 2). Researchers in about 20 countries are attempting to develop pathogens to control weeds in major crops such as rice, wheat, sorghum, soybean, sugar beet, citrus, vegetables, oil crops, and plantation crops, as well as in agroforestry, sod and turf, and ranch lands. Weeds of high economic importance such as Amaranthus spp., Chenopodium album, Convolvulus spp., Cyperus spp., Euphorbia heterophylla, Senna obtusifolia, Xanthium spp., various grasses and vines, parasitic weeds {Cuscuta spp. and Striga hermonthica), and several invasive annuals, aquatic weeds, and tree species have been targeted for inundative control by pathogens. In situations where the economics of weed control do not justify the use of costly control methods, such as in rangelands, natural areas, native forests, and certain natural waters, the option has been to use pathogens as classic biocontrol agents.