It is accepted in the scientific literature that agricultural intensification, including the use of large monocultures, results in increased damage by pests. The theoretical basis for this prediction is, however, unclear. This prediction has been supported by many empirical studies. However, most of these studies were conducted in relatively small plots or on perennial vegetation. We suggest that the extrapolation of these results to the large spatial scale of commercial agriculture and from perennial to annual vegetation could be misleading. We used a simulation model to explore the relationship between the field size of monocultural crops and season-long mean expected pest densities. We investigated how the underlying relationship between field size and pest densities might be influenced by the presence/absence of an effective natural enemy; by the relative dispersal abilities of the pest and natural enemy; by the ability of the pest and natural enemy to overwinter within the crop habitat; and by the pest’s rate of reproduction in the crop. Our model predicts that the relationship between field size and pest densities may, under commonly satisfied conditions, assume any of several forms (positive, negative, hump-shaped, or essentially constant), depending on the biology of the organisms. Each of the underlying relationships between field size of monocultural crops and expected pest densities may motivate adoption of a different set of pest management tactics. Whereas positive relationships motivate tactics that facilitate early natural enemy colonization of the interior of large monocultures (e.g., provision of supplemental food resources within the crop), negative relationships may instead motivate a suite of farm-design approaches that reduce pest colonization of crop interiors by achieving larger functional field sizes (e.g., aggregating multiple fields of the same crop).