304 Influence of Late Thinning with NAA and Carbaryl in the Apple Cultivar Braeburn

Abstract

NAA (1-naphthaleneacetic acid) is widely used for thinning apples; however, its mechanism of action is not well understood. Postbloom application of NAA is cultivar-specific and may, in addition to causing fruit abscission, show unwanted side effects. The response of 5-year-old `Braeburn'/MM 111 apple (Malus domestica Borkh.) trees trained to palmette leader to NAA used alone or in combination with carbaryl (1-naphthyl-N-methylcarbamate) was evaluated in late thinning trials. The experiment was conducted at the Comahue National Univ. (lat. 38°56′S long 67°59′W), during the 1997-98 growing season. Treatments were 1) control, 2) NAA (13 ppm), and 3) NAA (6.5 ppm) + Carbaryl (600 ppm). Whole sprays were applied 17 Oct. at 22 days after full bloom (DAFB) to five trees per treatment. Fruit diameter (FD) was recorded twice weekly (n = 20 per date and treatment). At 169 DAFB, cropload and fruit fresh weight (FW) were determined. Fruit were then graded into size categories. Analysis of variance was used and mean separations were computed with Student's t test. Good thinning resulted from NAA applications; however, this did not reflect in increased mean FW. The number of fruit ≥70 mm was increased by 6.67%. Cropload was overthinned by NAA + carbaryl. Mean FW was slightly greater than control (185.15 and 172.45 g, respectively) and this treatment resulted in 90 % of the fruit ≥70 mm compared to 75 % from control. The following potential model best fitted the fruit growth pattern on non-thinned trees: FD =2.9077 DAFB0.6307 (R2=0.98, P≤0.001). More work needs to be done to establish the most effective timing and concentration of spray for `Braeburn' to give the maximum crop of large fruit on a regular cropping basis.