The effects of Apogee® on shoot growth, secondary flowering, fire blight, fruit quality, yield and return bloom in ‘Bartlett’ pear growing in California

Abstract

SummaryApogee® sprays were applied to mature ‘Bartlett’ pear (Pyrus communis L.) trees as single or multiple sprays during the growing seasons of 1999 to 2003 at concentrations of 420 g ha–1 (125 mg –1) or 840 g ha–1 (250 mg–1): both reduced vegetative shoot growth. Two sprays of 840 g ha–1 applied 3–3.5 weeks apart were most effective and reduced shoot growth by approximately 40%. An application made 2 d after fall bloom was ineffective and led to more vegetative shoot growth. Single sprays of Apogee® made within 9–28 d after full bloom (DAFB) were equally effective in reducing vegetative shoot growth. Bourse shoot growth was reduced 43% by 3 April, 2001 (8 DAFB) treatment of 840 g ha–1 when bourse and vegetative shoots ranged from 2.5 to 7.5 cm in length. Subsequent single applications of 840 g ha–1 Apogee® (on April 12 or 23, 2001) did not reduce bourse shoot growth significantly. Vegetative shoot growth was also reduced by 12% (9 d after treatment) and by 38% (approximately one month after treatment) by 840 g ha–1 Apogee® applied on 3 April, 2001, (8 DAFB). In 2002, bourse shoot growth was controlled most effectively by split applications (840 + 420 g ha–1 or 840 2 g ha–1, 9 April and 24 May) and by 840 g ha–1 Apogee®, applied at 2.5 to 7.5 cm shoot growth (9 April). These split applications, as well as girdling, decreased shoot strikes in 2002, the year after treatment. Split applications of 840 g ha–1 Apogee® made in April to early May were most effective in controlling both vegetative and bourse shoot growth in most years, although single applications of Apogee® were effective in some years. Subsequent flushes of shoots tended to be controlled by split applications with the second application timed to the emergence of new shoots. Apogee® was not consistently effective in reducing the incidence of Type I or Type V secondary flowers in these trials. Single or multiple sprays of Apogee® had no measurable or consistent effect on return bloom, fruit size or shape, firmness, percentage soluble solids, or yield per tree over the period of these experiments. Apogee® appears to have promise as a shoot growth control agent in ‘Bartlett’ pear growing in California, USA, without deleterious effects.