CHEMICAL THINNING OF GOLDEN DELICIOUS APPLE WITH NAAM AND/OR CARBARYL IN COMBINATION WITH A SPREADER AND THE ANTI-RUSSETING AGENT GA₄₊₇

Although in itself ineffective, Regulaid enhanced the thinning effect of low concentrations of NAAm and carbaryl to the level obtained with normal concentrations. This will make it possible to economize on chemical thinners. Regulaid did not increase the thinning effect of normal concentrations of NAAm and carbaryl, but when NAAm and carbaryl were sprayed subsequently on the same trees Regulaid enhanced thinning excessively.

Further, 63 ppm NAAm thinned only slightly more than 21 ppm, and 750 ppm carbaryl thinned to the same degree as 250 ppm. NAAm thinned less than carbaryl.

In three other trials, NAAm (63 ppm) and/or carbaryl (750 ppm), applied as mentioned above, were used in combination with an anti-fruit russeting spray programme with the gibberellin mixture A₄ + A₇ (GA₄₊₇; four sprays of 10 ppm every 10 days starting at petal fall). The GA₄₊₇ treatment alone was also included in the trial.

GA₄₊₇ not only had a suppressive effect on fruit russeting but also acted as a mild fruit thinner. Combination of GA₄₊₇ sprays with NAAm and/or carbaryl increased the thinning effect of the latter but not always. When all three chemicals were used overthinning occurred. The thinning effect of NAAm plus GA₄₊₇ was of the same order as that of carbaryl alone. Because this combination favoured skin finish, it can replace carbaryl in thinning programmes.

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