Combining ethephon and naphthalene acetic acid (NAA) in one spray to thin 'Golden Delicious' apples

A trial examined the effects of using ethephon or naphthalene acetic acid (NAA) alone or in combination to thin 'Golden Delicious' apples. All sprays were applied only at full bloom (FB). A factorial design was used with ethephon sprays of 0, 50, 100, and 200 mg/litre and NAA at 0, 5, 10, and 20 mg/litre with an additional treatment hand thinned just after FB. Ethephon applied alone thinned effectively at 100 or 200 mg/litre. NAA applied alone did not thin at any concentration. The three concentrations of NAA with ethephon at 50 mg/litre improved thinning over the untreated control but not enough to significantly improve fruit weight and size. Ethephon alone at 100 mg/litre thinned very effectively and as well as any combination with NAA. Fruit weight and size were improved by all treatments using ethephon at 100 mg/litre. There was no advantage using ethephon at 200 mg/litre when compared to 100 mg/litre. Although there was some evidence that the combination of ethephon and NAA at the highest concentrations removed more fruit than ethephon alone at 200 mg/litre this was not reflected in better fruit weight or size. There is no advantage in adding NAA to ethephon to thin 'Golden Delicious' at FB and ethephon at 100 mg/litre would be the thinning spray of choice. © 1994 The Royal Society of New Zealand.