PHYTOTOXIC INTERACTION OF TRIDIPHANE AND METRIBUZIN IN METRIBUZIN SENSITIVE AND TOLERANT SOYBEAN (GLYCINE-MAX) AND TOMATO (LYCOPERSICON-ESCULENTUM)

The joint action of metribuzin and tridiphane was investigated in metr ibuzin-tolerant (T) and metribuzin-susceptible (S) soybean and tomato cultivars within species, respectively, under growth room studies. Map le Arrow (T) and Maple Amber (S) exhibited similar tolerance to tridip hane applied at soybean emergence. Vision (T) tomato was more sensitiv e to tridiphane than was Springset (S) tomato, the reverse of the rela tive tolerance to metribuzin. A phytotoxic interaction was demonstrate d following application of tridiphane and metribuzin at the respective rates (kg ai ha(-1)) of 0.1 and 1.1 in Maple Arrow (T) soybeans, 0.05 and 0.25 in Maple Amber (S) soybeans, and 0.25 and 0.2 in Springset ( S) tomato. Tridiphane applied 1 or 4 h before metribuzin caused the gr eatest phytotoxicity in Maple Amber (S) soybeans. Soybean field result s generally supported those of growth-room studies. Foliar spray pretr eatment with tridiphane increased total radioactivity in Springset (S) , decreased the total root radioactivity and increased total shoot rad ioactivity in both Vision (T) and Springset (S) and decreased metaboli sm of metribuzin to water soluble conjugates in Springset (S) roots ov er 24 h following C-14-metribuzin application to roots of intact tomat o seedlings. The increased uptake, translocation to the shoots, and de creased root metabolism of metribuzin in Springset when pretreated wit h tridiphane could explain the phytotoxic interaction (which was unexp ected, based only on the glucose detoxification pathway of metribuzin in tomato).