Abstract
Residual effects of single applications of 1000 and 2000 ppm succinic acid 2,2-dimethylhydrazide (SADH) in mid-July or mid-August, 1969, were determined. Mid-August treatment of 2000 ppm SADH inhibited June drop, depressed fruit size and increased fruit set; but it did not affect flowering, seed content and viability during June drop, preharvest drop, flesh firmness, or yield in 1970. Flowering and yield were often reduced in 1971 where SADH was applied in 1969. The results suggest that under some circumstances the residual effects of SADH may tend to induce biennial bearing of ‘McIntosh’ apple trees.