Herbicide Interactions with Fungal Root Pathogens, with Special Reference to Glyphosate

Abstract

Weeds are the most economically important of all pests with respect to sales of pesticides and limitations to crop yields (62). Herbicide sales represent more than two thirds of the 436 x 106 kg of pesticides used annually in United States (113), and almost one half of the $21 billion worldwide pesticide market (8). Numerous cases where an herbicide treatment influences disease outcome have been studied by plant pathologists as well as weed scientists. The concepts and the literature on interactions between herbicides, microorganisms, and plant diseases have been extensively reviewed (2-4, 40, 51, 59, 78, 129, 150). Most of the literature on herbicides deals with their direct effects on weeds and the effects of weed control on crops (Figure 1A). The effects of herbicides coming in direct contact with crops are considered secondarily in the weed-management literature (Figure 1B). The protection or predisposition of crops to disease that is sometimes observed following the use of herbicides is of particular interest to plant pathologists. As we document in this review, herbicides can alter soil ecosystems by having a direct effect on various components of the soil microflora, such as