EFFECTS OF PACLOBUTRAZOL AND CARBARYL ON THE YIELD OF HI-EARLY RED DELICIOUS APPLES

A trial at Spreyton in north-western Tasmania compared the effects of paclobutrazol and carbaryl sprays on fruit thinning of apples. Untreated control and hand thinned trees were compared with trees treated with paclobutrazol or carbaryl alone or combinations of both. Paclobutrazol was applied 28 and 49 days after full bloom (AFB). The 28 day AFB paclobutrazol sprays were at rates of either 62.5 or 125 ppm of active ingredient followed by 62.5 ppm 49 days AFB. Carbaryl was applied at 1000 ppm at 10, 17 or 24 days AFB. Although several treatments removed more fruit than the controls, only two treatments thinned to less than the desired crop load, represented by the hand thinned treatment. These overthinned treatments were combinations of paclobutrazol applications and carbaryl sprayed 24 days AFB. It is recommended that if paclobutrazol programmes are to be initiated 28 days AFB, that carbaryl should not be sprayed later than 17 days AFB. Also, if carbaryl is sprayed late it is preferable to use paclobutrazol at 62.5 ppm rather than 125 ppm at 28 days AFB.