CHEMICAL BLOSSOM THINNING OF 'KAKAMAS' AND 'KEISIE' PEACH (PRUNUS PERSICA [L.] BATSCH.) CULTIVARS

Blossoms and small fruit are usually removed manually from canning peach cultivars to attain commercially acceptable fruit size. Armothin^®, a registered blossom thinning agent, was applied at different blossom stages to ‘Kakamas’ and ‘Keisie’ canning peach cultivars. ‘Kakamas’ was treated with Armothin^® (AT) at 2% v/v, applied either at full volume (FV), half (HV) or quarter (QV) volumes using a motorized knapsack mist-blower. The surfactant ‘DuWett^®’ (DW) was added at 0.5, 1.0 or 2% v/v to the HV and QV applications. ‘Keisie’ was treated with AT at 2 or 4% v/v applied at FV without DW, or at HV or QV with 0.10 or 0.25% v/v DW. Control trees were either not thinned or hand thinned to commercial standards. The percentage blossoms in each blossom stage of ‘Kakamas’ differed only during the second and third applications when most buds were either dormant (~67%) or at petal fall (45%). ‘Kakamas’ fruit per tree and fruit size were affected more by the application date. All treatments applied during the first two applications had larger fruit (~123 g) than the third application (101 g). To reduce spray volume of AT, HV or QV AT plus either 0.5 or 1% v/v DW may be used when most buds are dormant. The number of blossoms in each blossom stage of ‘Keisie’ differenced little during the three applications, with most blossoms (~20%) at petal fall. Only treatments affected fruit per tree and fruit size. 4% AT FV had less fruit per tree than the unthinned control and the same fruit size (127 g) as the hand thinned control (131 g). Either 2 or 4% AT may be used only at FV. DW did not compensate for the reduced volume. The effect of blossom stage of ‘Keisie’ on fruit thinning could not be determined.