Plant damage in urban agroecosystems varies with local and landscape factors

Biotic and abiotic factors at local to landscape scales influence insect pest and disease dynamics in agricultural systems. However, relative to studies focused on the importance of these drivers of crop plant damage in rural agricultural systems, few studies investigate plant damage from herbivore insects and plant diseases in urban agroecosystems, and consequently, most urban farmers lack knowledge on crop protection tactics. Here we use three common crop species within urban agroecosystems (community gardens) distributed across an urban landscape as a model system to ask how local, landscape, and microclimate factors relate to herbivore and disease plant damage. We hypothesized that plant damage would be lower in gardens with greater local vegetation complexity, landscape-scale complexity, and less variable temperatures, but that the importance of factors is species- and damage-specific. By measuring Brassica, cucurbit, and tomato insect pest and disease damage across the growing season, we confirmed that the importance of factors varies with crop species and by damage type. Both local complexity factors (e.g., number of trees and shrubs) and landscape complexity (percent natural cover in the landscape) relate to lower incidence of herbivore and disease damage on some crops, supporting our prediction that habitat heterogeneity at both local and landscape scales lowers plant damage. Greater temperature variability related to higher disease damage on tomatoes linking microclimate factors to disease prevalence. Yet, local complexity factors also related to higher incidence of plant damage for other crop species, indicating variable species-level impacts of local management factors on plant damage. By measuring the abundance of fungus-feeding lady beetles (Psyllobora) on cucurbits, we confirmed a strong association between natural enemies and powdery mildew. We provide a case study on how changes in local to landscape-scale factors relate to plant damage in urban agroecosystems and suggest how urban farmers and gardeners can apply this ecological knowledge to improve sustainable urban food production.