THE EFFECT OF ETHEPHON, NAA, BA AND THEIR COMBINATIONS ON THINNING INTENSITY OF 'SUMMERRED' APPLES

The chemical thinning of 'Summerred'/M.9 was investigated on three years old apple trees. The application of ethephon 200 ppm was done at the start of flowering time, 6-benzyladenine (BA) 100 ppm and 1- naphthaleneacetic acid (NAA) 10 ppm was applied at 10 mm fruitlet diameter and the combination spraying of these thinners was done as a multiple (ethephon + BA, ethephon + NAA) or tank mix (BA + NAA) application. The alone application of ethephon or NAA reduced the final fruit number but did not enhance the mean fruit weight, similar as the consecutive (multiple) application of ethephon and NAA. On the contrary, when BA was applied (alone or in combination with ethephon) a nice fruit growth happened after the thinning of fruitlets. The tank mix spraying of BA + NAA reduced the fruit number adequately and the fruit growth was enhanced. The strongest thinning (overthinning) occurred when ethephon spraying was followed by the mixture of BA and NAA three weeks later. Significantly better return bloom was observed in the case of BA and NAA alone application, ethephon + BA, BA + NAA and ethephon + BA + NAA treatments