An account is given of the causes and severity of secondary leaf fall of rubber, (Colletotrichum gloeosporioides [Glomerella cingulata] and Oidium heveae) its control, the choice of defoliant, trials with potted seedlings and aerial spraying. A correctly timed aerial application of cacodylic acid [RPP 51, 3698 a, b et passim] uniformly defoliates the trees before the onset of natural wintering. The new foliage therefore matures earlier and avoids secondary leaf fall.