EFFECTS OF CERTAIN NEMATICIDES ON SOIL NITROGEN, SOIL NITRIFIERS, AND POPULATIONS OF PRATYLENCHUS PENETRANS IN FLUE-CURED TOBACCO

Abstract

Field experiments were conducted in 1973 and 1974 on Fox loamy sand to study the effects of Telone (1,3-dichloropropene and related C3 hydrocarbons), Telone C (1,3-dichloropropene and related C3 hydrocarbons 85%, and chloropicrin 15%), Vorlex (1,3-dichloropropene and related C3 hydrocarbons 80%, and methyl isothiocyanate 20%), and the non-fumigant nematicide oxamyl (methyl N′,N′-dimethyl-N-[(methyl-carbamoyl)oxy]-1-thiooxamimidate) on soil nitrifying bacteria, soil nitrogen, and Pratylenchus penetrans (Cobb) Filip, and Stek. 1941 in flue-cured tobacco. Chloropicrin and triazophos (1-phenyl-3-(0-0-diethylthionophosphoryl)-1, 2, 4-triazole), a non-fumigant, were also included in 1974. Soil treated with fumigant nematicides was higher in NH4+-N than untreated soil or soil treated with non-fumigant nematicides. Lower levels of NO3−-N were found in the soil 37 days after fumigation with Telone or Telone C and 28 days with Vorlex. Fumigant nematicides increased total mineralization, (NH4+ + NO3−)-N, of organic nitrogen in the soil; the effect lasted longer with Telone C and chloropicrin. Nitrosomonas spp. were higher in Telone- or Telone C-treated plots at 4 wk after fumigation and higher in all nematicide plots at 8 wk. Nitrobacter spp. were higher with Vorlex and oxamyl than in the check plots at 4, 6, and 8 wk after fumigation. Nematicides reduced the population of P. penetrans in the soil throughout the season in 1973 but control was less consistent in 1974. Oxamyl and triazophos gave good control of nematodes in roots of flue-cured tobacco. All nematicides tested gave an increase in yield of tobacco in 1973 but no significant increases were obtained in 1974.