Vol. 70 No: 2

Title:
Benzyladenine and Carbaryl Effects on Fruit Thinning and the Enhancement of Return Flowering of Three Apple Cultivars

Authors:
S.J. MCARTNEY, D.S. TUSTIN, S. SEYMOUR, W. CASHMORE and N.E. LOONEY

pp: 287-296

Abstract:
Mature ‘Royal Gala’/MM.106, ‘Jonagold’/MM.106, and four year old ‘Braeburn’/M.793 apple trees were treated with 6-benzyladenine (6-BA) or carbaryl at rates and times after bloom intended to reduce fruit set at spur sites (an early spray) or at lateral flowering sites (a later spray). ‘Royal Gala’: neither carbaryl nor 6-BA reduced overall fruit set early in the growing season although carbaryl did reduce the number of spur sites that set three or more fruit, increased the number with only one fruit, and increased mean fruit weight at harvest. ‘Braeburn’: the late 6-BA application excessively reduced fruit set of both spur and lateral clusters whereas the early spray was effective only on spur clusters. Compared to an unthinned control, carbaryl, at both treatment times, reduced overall fruit set but exhibited greater activity on spur clusters. ‘Jonagold’: overall fruit set was reduced by carbaryl at two of three application times whereas 6-BA was largely without effect. Carbaryl reduced fruit set on lateral clusters more effectively than on spurs. Return flowering of ‘Braeburn’ was enhanced by the ‘late’ spray of either 6-BA or carbaryl. This effect was similarly expressed on spurs and laterals but neither chemical promoted return flowering of spurs that fruited in the year of treatment. Overall return flowering of ‘Jonagold’ appeared to be enhanced by the 6-BA sprays; spurs that did not crop in the year of treatment were most responsive to 6-BA. Conversely, carbaryl appeared to have its greatest return flowering effect on strong, well exposed ‘Jonagold’ spurs that bore fruit in the year of treatment, despite the fact that the presence of even one fruit on a spur was sufficient to greatly reduce the chances of return flowering of that spur. Furthermore, fruit set per ‘return’ flower cluster tended to be higher on ‘Jonagold’ trees treated with carbaryl the previous season. Neither chemical enhanced return flowering of ‘Royal Gala’. Carbaryl increased specific leaf weight of ‘Jonagold’ spur and lateral fruiting sites and increased leaf number and bourse length on fruiting spurs, suggesting a possible mode of action for this chemical thinner.

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