Summer pruning of apple: impacts on disease management

Abstract

Pruning, including summer pruning, of apples can have a positive impact on disease management in two basic ways: through removal of dead tissue and inoculum, and through alteration of the canopy microclimate. Summer pruning can also increase diseases if it is done when disease risk is high. However summer pruning is used almost exclusively as a horticultural tool to improve fruit quantity and quality. As orchard planting and training systems have moved from semi-dwarf trees to high-density, fully-dwarf trees, very few summer pruning studies have looked at impacts related to disease, yet summer pruning in high-density systems may have important disease management effects. Growers should avoid summer pruning practices which will increase disease risks, and use those that offer both horticultural and disease management benefits. More research in this area is needed, as cultural components of apple disease management will become increasingly important in sustainable production systems. This review looks at important apple diseases, including apple scab, fire blight, sooty blotch and flyspeck, black rot, white rot, Nectria canker and powdery mildew, and uses dormant pruning studies plus knowledge of the epidemiology of the diseases to suggest ways that summer pruning would be expected to impact disease management.