Triphenyltin acetate residues on potato leaves in blight spraying trials

Spraying the potato variety Ulster Supreme with triphenyltin acetate delayed the spread of Phytophthora infestans in 1960 and increased the gross yield of tubers from 13.5 in the unsprayed controls to 16.3 tons/acre. The sprayed plants also had fewer infected tubers and consequently the net weight of healthy tubers was increased by 3.8 tons/acre. A method for measuring triphenyltin acetate residues on celery was adapted to measure residues on potato leaves and tubers. The top and bottom leaves of plants had 31 and 36 p.p.m. of triphenyltin acetate immediately after the crop was sprayed; 2 weeks later the residues were 10 and 12 p.p.m. Tubers had < 0.3 p.p.m. which was indistinguishable from the apparent content of tubers from unsprayed plants.