Biennial bearing in tree fruit can be problematic, and these patterns are not unique to tree fruit and occur in natural species. Masting, or the abundant production of seeds in some years, can also be observed in natural tree species. Despite extensive research, biennial bearing still affects commercial orchard production. Biennial bearing cycles are costly, with inconsistent yields and fruit quality occurring yearly. Crop load management is one commonly used management strategy to control biennial beating. However, trees can continue a biennial cycle the year following adequate crop thinning. We evaluated six different agronomic strategies to combat biennial bearing in apple trees; two for low-cropping trees (“off” year) and four for high-cropping trees (“on” year). In 2023, ‘Honeycrisp’ trees on B.9, G.41, G.890, and M.9-T337 rootstocks in their high-cropping year were root pruned, girdled, sprayed with ethephon, or fertilized with nitrogen (ammonium nitrate) in the fall, along with untreated control. Trees in their low-cropping year (2023) were defoliated and sprayed with gibberellic acid (GA 3 ) and untreated control. Due to the limited availability of low-cropping trees in 2023, only ‘Honeycrisp’ trees on B.9 and M.9-T337 rootstocks were used. All treatments were applied two to three weeks after full bloom except for nitrogen fertilization, which was applied in late August. Crop load, vegetative growth, and fruit quality were measured for treated trees and controls. Carryover effects of treatments were calculated to quantify the reduction/amelioration of biennial bearing incidence. In low-cropped trees, GA 3 had significantly higher return bloom from controls and defoliated trees. In high-cropped trees, no treatment had a significant effect on return bloom compared to controls. Vegetative growth was not affected by any treatment. Effective agronomic strategies for managing biennial bearing can be inconsistent and need to be further investigated for their impacts.
