The Effect of Certain Herbicides on Soil Microorganisms

Interactions between herbicides and plant pathogens

“…Ammonium thiocyanate and AMS suppressed actinomycetes and increased fungi only in starch-amended soil (SMITH et al 1945). Since herbicides decrease the population of plants, they may decrease the amount of easily degradable organic matter in the soil.…”

Unexpected Side Effects of Herbicides: Modulation of Plant-Pathogen Interactions

“…As an interesting side effect, the biological activity of herbicides extends beyond their effect on target organisms and herbicides may influence plant-pathogen interactions through their effect on the pathogen, the plant, or on the surrounding soil organisms including symbiotic interactions. This phenomenon was first observed in the early 1940s by Smith et al (1946) and described in more detail since 1960. Several studies examining the direct effects of various herbicides on plant pathogens and disease development have been published.…”

Microbiology of Soil

“…Most popular of the latter are vari ous derivatives of 2,4-dichlorophenoxyacetic acid (2,4-D). Smith et al (160) found no significant effect of 2,4-D on the total plate counts, actinomyces, fungi, and protozoa at concentrations up to 500 p.p.m. The nitrifying bacteria, however, were definitely in jured with 100 p.p.m.…”