Thinning apples and pears in a nordic climate 1. The effect of NAA, ethephon and lime sulfur on fruit set, yield and return bloom of four pear cultivars
1996
Meland, M. | Gjerde, B. (Planteforsk - Norsk Inst. for Planteforskning, Ullensvang Forskingssenter, Lofthus (Norway))
A field experiment examined the effect of using naphthalene acetic acid (NAA), lime sulfur and ethephon to thin four pear cultivars. NAA at three concentrations; 10, 20 and 30 mg/l and 5 lime sulfur with or without the addition of 150 mg/l ethephon were applied at petal fall and full bloom to the same trees for a period of three years, respectively. The effects of NAA were largely additive; fruit set, yield and fruit number decreased with increasing concentration. Neither thinning nor return bloom were promoted of a low dosage of ethephon. All cultivars, except 'Amanlis', became biennial during the experiment. At heavy bloom density 10 mg/l NAA thinned 'Amanlis', 20 mg/l 'Keiserinne' and 'Moltke' and 20 -30 mg/l 'Clara Frijs' adequately. Lime sulfur produced some thinning on 'Amanlis' and 'Moltke'. The thinning had little impact on return bloom. Minor phytotoxic symptoms of the highest concentrations of NAA were observed.
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