Carbaryl as a Fruit Thinning Agent

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Abstract
Summary The results are presented of fruit thinning studies carried out over several years with the apple varieties Laxton’s Superb and Worcester Pearmain. The thinning activity of carbaryl was negligible at 0·0028% a.i. but increased rapidly over the range 0·0083% to 0·075%. Comparatively little additional thinning resulted from a further increase in concentration. In Worcester Pearmain thinning was stimulated by applications of carbaryl over a 4–5 week period from petal fall, the cessation of thinning activity coinciding with the end of the main period of natural fruitlet shedding. The intensity of thinning was greatest at petal fall and declined with delay in application. This decline was not continuous but showed two intervals of 7 to 13 days duration during which the intensity of thinning remained relatively constant. Up to 12 days elapsed between application and the commencement of induced fruitlet shedding. Carbaryl was found to thin within, rather than between, fruitlet clusters, and to stimulate the abscission of lateral fruitlets more than terminal ones. The growth of young fruitlets was retarded for a short period following the application of carbaryl, but as a result of thinning the size of mature fruit was increased. In the year after treatment increased blossoming and cropping was most marked with biennial trees of Laxton’s Superb. With regularly cropping trees of Worcester Pearmain, although thinning induced a moderate increase in subsequent blossoming, no residual effects on cropping were detected.

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