Effect of Selected Herbicides on Bacterial Growth Rates

Abstract

Specific growth rate constants were used to evaluate the effects of selected herbicides on Erwinia carotovora, Pseudomonas fluorescens , and Bacillus sp. Comparison of growth rate constants permitted the identification of either stimulatory or inhibitory effects of these substances. E. carotovora was inhibited by 6,7-dihydrodipyrido(1,2-a:2′-c)pyrazinediium (diquat) and 4-hydroxy-3,5-diiodobenzonitrile (ioxynil) at 25 μg/ml; 1,1′-dimethyl-4,4′-bipyridinium (paraquat) at 50 μg/ml; and pentachlorophenol (PCP) at 10 μg/ml. P. fluorescens was inhibited by paraquat and PCP at 25 μg/ml and by 4-amino-3,5,6-trichloropicolinic acid (picloram) at 50 μg/ml. Stimulation of P. fluorescens was observed with 4-(methylsulfonyl)-2,6-dinitro- N,N -dipropylaniline (nitralin) at 25 μg/ml. The Bacillus species was inhibited by diquat (25 μg/ml), ioxynil (10 μg/ml), and paraquat and PCP (5 μg/ml). No significant effect of 2-chloro-4-(ethylamino)-6-(isopropylamino)- s -triazine (atrazine), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), α,α,α-trifluoro-2,6-dinitro- N,N -dipropyl- p -toluidine (trifluralin), or 1,1-dimethyl-3-(α,α,α-trifluoro- m -tolyl)urea (fluometuron) on growth rates of the bacteria was observed at 25 and 50 μg/ml.