Abstract
AbstractBiotic 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.
Highlights
In agricultural systems, farmers are continuously challenged by a wide range of crop‐damaging pests
While we present results from total plant damage as this may be important to production‐focused practitioners, we focus on the specific types of plant damage in our results and discussion
We investigated local and landscape factors associated with plant damage on three common crop species in urban agroecosystems using urban community gardens as a model system
Summary
Farmers are continuously challenged by a wide range of crop‐damaging pests. Bacterial, and fungal agricultural pests cause billions of dollars of crop damage annually (Losey and Vaughan 2006). Both biotic and abiotic factors affect the bottom‐. The resource concentration hypothesis predicts that higher concentrations of host plants and less vegetation diversity facilitate host plant location leading to herbivore and disease outbreaks Both of these hypotheses support the idea that local habitat heterogeneity reduces herbivore and disease outbreak both through herbivore and disease resource manipulation, and through increased herbivore and pathogen mortality by natural enemies to enhance pest control (Kremen and Miles 2012, Rusch et al 2013, Marja et al 2018). Agroecological practices grounded in ecological theory have potential to minimize crop plant damage and enhance crop production through on‐farm management of habitat structure (Garibaldi et al 2018), but further studies are needed
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