Rate of immigration from orchard ground cover into trees was the major determinant of T. urticae-days in the tree canopy: in low-immigration orchards, the generalist phytoseiid Typhlodromus pyri could easily suppress T. urticae but in high-immigration orchards the predator was overwhelmed. Weather was also important: immigration rates and T. urticae-days in trees were significantly greater in 2001, the warmer drier year, than in 2000 despite three-fold greater use of miticides in 2001. Use of the miticidal herbicide, glufosinate, in tree rows reduced rates of immigration in high immigration orchards but not sufficiently to prevent economic densities of T. urticae. We conclude that mite outbreaks in high immigration orchards were due to the failure of the specialist phytoseiid Amblyseius fallacis to regulate T. urticae in the ground cover and to follow their prey up into the tree canopy in the summer.