Effects of pesticides on soil enzymatic activities, Pratylenchus penetrans populations, black root rot, and growth of flue-cured tobacco

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Abstract
Field experiments were conducted on Fox loamy sand with nine treatments and three varieties of flue‐cured tobacco (Nicotiana tabacum) to study the effect of nematicides, Telone II, Telone C17, Vorlex, Vorlex CP, fenamiphos, and a fungicide, propamocarb on soil enzyme activities, populations of Pratylenchus penetrans (Cobb) Filip. and Stek, black root rot, and growth of tobacco. Fumigants and fungicide were applied on May 10 and fenamiphos was applied on May 17. Levels of NH4 +‐N in the soil were higher after treatment with most pesticides on May 24 and July 25 in the urease experiment. Dehydrogenase activity was inhibited by treatments of Telone C17 until June 27, and with Vorlex CP and propamocarb until June 13. Nematode counts before application of pesticides were 2000 to 4000/kg of soil. Populations of P. penetrans were lower in the fumigant‐nematicide treated plots throughout the experiment. Nematode population counts in tobacco roots of three varieties were sometimes lower with Telone II, Vorlex, Vorlex CP and Vorlex + propamocarb treatments than in the control tobacco roots. Occurrence of black root rot lesion in D‐76 variety was greater with Telone II and Vorlex on June 27. Less black root rot (Thielaviopsis basicola) incidences were observed on July 25 in fumigant nematicide treated plots of C‐18 variety; fewer black root rots lesion were observed in the black root rot susceptible variety WM tobacco after Telone C17 and Vorlex CP treatments. Significant growth of tobacco varieties in height and weight was observed with Telone C17 and Vorlex CP. Heavier root weights of the three varieties were increased with treatment of Vorlex CP. The increase in yield of tobacco resulted mainly from control of nematodes and black root rot.

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