Browsing by Author "Steenkamp, Human"

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    New chemical thinning strategies for stone fruit
    (Stellenbosch : Stellenbosch University, 2015-12) Steenkamp, Human; Theron, K. I.; Steyn, Willem J.; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: Thinning of stone fruit, just as in any other deciduous fruit crop, plays an important role in producing fruit of the right size and quality. Hand thinning is highly labor intensive and time consuming, thus an alternative method of thinning is important to the industry. Chemical and mechanical thinning either alone or in combination could be the alternative. Two chemicals, 1-aminocyclopropane-1-carboxylic acid (ACC) and 6-benzyladenine (6-BA) were evaluated on Japanese plums, cling peaches and nectarines. In addition, the Darwin 300™, a mechanical string thinner, was also included in trials on early maturing ‘Alpine’ nectarine and ‘African Rose™’ plum. In all trials the objective was to reduce the required hand thinning during commercial hand thinning without compromising on yield and fruit quality. In Japanese plums we were able to reduce the hand thinning requirement significantly with both the ACC thinning and mechanical thinning strategies. Regarding ACC, cultivars differed in their sensitivity to the chemical and the recommended rate will differ for cultivars. ACC consistently reduced the required hand thinning linearly with increasing rate. The recommended rate of ACC for ‘African Rose™’ is 600 μl.L-1 and for ‘Laetitia’ 400 μl.L-1. For ‘Fortune’ a recommended rate could not be determined at this stage, thus further trials should be conducted. The Darwin 300™ reduced hand thinning significantly without reducing the yield significantly. Combining the Darwin 300™ with ACC 600 μl.L-1 in ‘African Rose™’ gave promising results with regard to hand thinning requirement and fruit size, without reducing yield efficiency significantly. No leaf drop was observed on Japanese plums, except in the pilot trial when applications were made at high temperatures, which should therefore be avoided. ACC was effective as thinning agent in cling peaches. In ‘Keisie’, the results were positive during both seasons, and ACC reduced the hand thinning requirement without reducing yield efficiency. The recommended rate of ACC for ‘Keisie’ is 600 μl.L-1. Slight leaf drop was observed. In ‘Sandvliet’, there was a significant reduction in fruit set, without reducing the required hand thinning. The reduction in fruit set led to a significant reduction in yield. Severe leaf drop was observed, indicating that cultivars differ in sensitivity to ACC. ACC would not currently be recommended for ‘Sandvliet’. In nectarines, ACC only thinned ‘Turquoise’ but not ‘Alpine’ or ‘August Red’ at the rates and phenological stage used, again indicating cultivar differences in sensitivity. In ‘Turquoise’, the highest ACC rate (500 μl.L-1) reduced fruit set per tagged shoot, as well as the hand thinning requirement, but this rate also reduced the total yield. The Darwin 300™ evaluated on ‘Alpine’ reduced fruit set significantly and the hand thinning requirement without reducing yield efficiency, indicating that mechanical thinning is a viable option in nectarines. Slight leaf drop was observed in all nectarine trials and ACC would not currently be recommended for nectarines. 6-BA was included to combat ACC-induced leaf drop and was partially successful. The reason for the differences observed in response to ACC between cling peaches and plums on the one hand, and nectarines on the other, cannot currently be explained.