Pest and Disease Risk and Management in High-Density Perennial Crops: Current Knowledge and Areas of Future Research

High-density production has been increasing for numerous perennial crops in different parts of the world. Recent work suggests that high-density systems improve yields, fruit quality, and harvest efficiency. Yet, despite the increasing amount of acreage in high-density production, there has been surprisingly little comparative research on pest and disease patterns in such systems compared to conventional systems. Given the significantly different structure of high-density plantings compared to conventional orchards, pest abundance, disease prevalence, and appropriate management strategies are likely to differ. Here we describe the characteristics of high-density plantings and how their management and infrastructure are likely to have direct and indirect effects on pest abundance and disease prevalence. We also describe how high-density structure, management, infrastructure, fruit abundance, and microclimate present challenges and opportunities for pest and disease management strategies. For example, the compact structure of high-density plantings may mean smaller quantities of inputs are required while, at the same time, the high foliage density may reduce penetration of pesticide sprays and other inputs. Finally, we propose critical areas for future research including 1) patterns of pest and disease prevalence among rootstocks and varieties, 2) how infrastructure and timing of high-density management affect pest and disease prevalence, 3) how microclimate and fruit abundance vary across canopy levels, with associated impacts on pest and disease prevalence, and 4) types of pest and disease management that are likely to be effective in high-density systems.