EFFECTS OF THE NEMATICIDES DD AND MOCAP ON SOIL NITROGEN, SOIL MICROFLORA, POPULATIONS OF PRATYLENCHUS PENETRANS, AND FLUE-CURED TOBACCO

Abstract

Field studies were conducted for 2 yr on Fox loamy sand to compare the effect of broadcast DD (mixture of 1,3-dichloropropene, 1,2-dichloropropane, and related C3 hydrocarbons) and Mocap (O-ethyl S, S-dipropyl phosphorodithioate) on numbers of Pratylenchus penetrans (Cobb) Filip. and Stek. 1941, the nitrification processes in the soil, and the subsequent effects on flue-cured tobacco (Nicotiana tahacum L.) grown in a normal rye–tobacco rotation and, in 1 yr only, on an area fallowed the previous summer. Levels of NH4+-N in the soil in June tended to be higher, and NO3−-N lower with the DD treatment, applied in early May, than in the untreated check. Mocap had no apparent effect on soil NH4− and only inconsistent effects on soil NO3−. Although numbers of NH4+-N oxidizers and NO2−N oxidizers varied among treatments, the differences were inconsistent from week to week and did not appear to be related to soil NH4+ and NO3−. In 1971, DD and Mocap gave good nematode control, but yield and dollar value were not different than with the check. Although both nematicides gave satisfactory control of nematodes in 1972, only DD resulted in an increase in yield and value. The low yield in the Mocap and check plots in 1972 was probably due to loss of available N during a heavy June rainfall; soil N was less susceptible to leaching with the DD treatment, as a higher amount was in the NH4+ form.