CHEMICAL THINNING OF THE APPLE CULTIVAR 'SUMMERRED' WITH NAA AND CARBARYL

NAA at three rates: 7.5, 15, and 30 ppm with or without addition of 750 ppm carbaryl were applied at petal fall to two orchards in two years. The first year NAA caused a drastic reduction in fruit set with increasing concentration. Carbaryl gave little thinning, but in combination with NAA increased the effect of the low NAA rate and decreased that of the high rate. The following year thinning response to NAA was smaller and no interaction between the two compounds was found. The different thinning activity may be explained by different fruit set patterns in the two years. The first year many fruits were set in clusters, while the second year the largest proportion of clusters had only one fruit.