Response of selected soilborne fungi and bacteria to herbicides utilized in potato crop management systems in Maine

The response of nine soilborne fungi associated with potato production:Rhizoctonia solani, Fusarium solani ‘Coerculeum,’F. roseum ‘Sambucinum,’F. avenaceum, Helminthosporium solani, Verticillium alboatrum, Alternaria solani, Trihcoderma viride, andLaetisaria arvalis; and five soilborne bacteriaAzotobacter chroococcum, Bacillus subtilis, Erwinia carotovora subsp. carotovora,Pseudomonas aeruqinosa andPseudomonas fluorescens to the herbicides linuron, metribuzin, dinoseb, paraquat, EPTC, and dalapon were determined by growth on amended media. None of the herbicides increased radial growth of the fungi, and only dinoseb significantly (P = 0.05) reduced radial growth of all fungi at concentrations less than 64 ppm. EPTC, dalapon, linuron, paraquat, and dinoseb severely inhibited bacterial survival (91, 82, 44%, respectively) when evaluated on trypticase soy and cimmons citrate agar media amended with herbicides at concentrations of 1, 10, and 100 ppm. Dinoseb, when applied to field soil in pots, significantly reduced total microorganism populations in the top 5 cm of soil. Results suggest that soil applications of herbicides can selectively inhibit soil microflora with possible effects on disease incidence and severity, and may also be a factor in determining effectiveness of biolgical control agents.