Certain chemical thinning treatments advance maturity of Paulared apple

Mature Paulared (Malus ×domestica Borkh L.)/MM106 apple trees with a heavy bloom were sprayed with carbaryl [Sevin® XLR 1.25 mL L–1 (600 mg L–1 a.i.)], benzyladenine (BA)/gibberellic acids (GA4 + 7) [Accel® 1.22 mL L–1 (23.1 mg L–1/2.31 mg L–1 a.i.)], carbaryl [Sevin® XLR 1.25 mL L–1 (600 mg L–1 a.i.)] + BA/GA4 + 7 [Accel® 1.22 mL L–1 (15.6 mg L–1/1.56 mg L–1 a.i.)] and napthaleneacetic acid (NAA) [FruitoneN® 0.32 g·L–1 (1.13 mg L–1 a.i.)] when fruitlet diameter was 7 mm. Ethephon [Ethrel® 2.29 mL L–1 (549.6 mg L–1 a.i.)] was applied at the 13.5 mm fruitlet diameter stage. Carbaryl alone, NAA and ethephon all resulted in improved fruit size at harvest, whereas BA/GA4 + 7 was ineffective as a thinner and did not alter fruit size at harvest. Of these treatments, only ethephon significantly reduced crop load. Both NAA and ethephon, and especially ethephon, advanced fruit maturity at harvest as indicated by a lower Streif index. Only ethephon increased commercial levels of fruit colour and following-year blossom density. Thus, while ethephon appears promising as a fruitlet thinner and a promoter of maturity for this cultivar, these effects will have to be balanced against possible adverse effects on storage and shelf life. Key words: Crop load, carbaryl, ethephon, apple maturity, Streif index