THE PHYTOTOXIC EFFECTS OF D.D.T., B.H.C., PARATHION AND TOXAPHENE ON TOBACCO

Abstract

No phytotoxic effect was seen following a pre‐sowing spray of tobacco seed‐beds with 27 lb./acre technical D.D.T. or after an application of the same material at 75.6 lb./acre to 3‐week‐old tobacco seedlings.A pre‐sowing application of parathion (diethyl paranitrophenyl thiophosphate) (2 % dust) at 1–8 lb. parathion per acre had no harmful effect. Used on 3‐week‐old tobacco seedlings at the excessive rate of 22.7 lb./acre it caused serious stunting and many deaths.Toxaphene (chlorinated camphene: empirical formula C10H10Cl8), applied as a 25 % wettable powder in a pre‐sowing spray at 6‐4 lb. toxaphene per acre, did not injure tobacco seedlings.No residual phytotoxic effects appeared in beds re‐sown 4 months after being treated with parathion or toxaphene at the pre‐sowing doses given above.Benzene hexachloride, applied before sowing at doses above 1.6 lb. technical B.H.C. per acre, suppressed root development in newly germinated tobacco seedlings. B.H.C. dusts used on n‐day‐old seedlings at 2–25 lb. technical B.H.C. per acre caused temporary distortion and stunting. Up to 11 lb./acre these symptoms were transitory: at 37.5 lb./acre many plants were killed and the remainder severely stunted. Resistance to these phytotoxic effects increased with age of plant, but 3‐week‐old tobacco seedlings showed considerable mortality after the application of 75.6 lb./acre of technical B.H.C.Beds re‐sown 4 months after the application of 6‐4 and 12.8 lb. respectively of technical B.H.C. per acre showed no phytotoxic effect, but, as tobacco seed is sown on the soil surface, the effect of the B.H.C. may have been merely masked, and it is not safe to assume that there was no residual effect. The actual persistence of B.H.C. in the soil was not determined.The possible mechanism of action of the B.H.C. effect is discussed.