Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 8, 2004
Publication Date: N/A
Interpretive Summary: Most apple trees, regardless of the rootstock, produce excessive vegetative growth. Overly vigorous growth reduces fruiting, lowers fruit quality, increases the need for dormant pruning, and reduces spray efficiency. Apogee is a new plant bioregulator that has shown promise for reducing excessive vegetative growth in apple without adversely affecting fruit quality. Because growth is reduced we wanted to know if the photosynthetic capacity of the tree was affected. Apogee sprays were applied to 'Delicious' apple trees at recommended times and rates and the effects on shoot and fruit growth and the whole-tree canopy were determined. Apogee reduced shoot growth, increased the number of fruit set, and reduced leaf area, but did not reduce whole-tree photosynthesis. This information is valuable to researchers and extension personnel and provides assurance to apple growers that Apogee does not have a negative impact on the photosynthetic performance of trees.
Technical Abstract: Vegetative growth management is essential in a modern high density apple planting to reduce pruning costs and prevent excessive vegetative growth that reduces light and spray penetration into the canopy, lowering fruit quality and return bloom. Plant growth regulators have been used since the 1960's to inhibit shoot elongation and help maintain apple tree canopies within the allotted planting space. This study examines the effect of multiple spray applications of Apogee on shoot growth and whole-canopy photosynthesis (WCPn) rate in young, bearing apple trees. Apogee increased fruit numbers and reduced shoot growth and inconsistently reduced leaf area; however, the reduction in photosynthetic area did not result in reduced WCPn or a detrimental effect on the fruit number:fruit size relationship. The use of Apogee for canopy management may produce a side-effect of increasing fruit set, which may be managed through a crop thinning program.