INFLUENCE OF CANOPY MICROCLIMATE ON INCIDENCE AND SEVERITY OF DOGWOOD ANTHRACNOSE

Incidence and severity of dogwood anthracnose within the interior and exterior canopies of exposed dogwood (Cornus florida L.) trees and canopies of understory trees were recorded over a 53-day period during the summer of 1990. Concurrent measurements of vapor pressure deficit, air temperature, evaporative potential, and photosynthetically active radiation within the canopies were also recorded. Disease incidence was significantly lower in the exterior canopy of exposed trees than in other canopy locations. Disease severity was significantly different among all three canopy locations, with the lowest severity in exterior canopies of exposed trees and the greatest severity in canopies of understory trees. Of the climatic variables measured, evaporative potential provided the most consistent contrast among microclimates at the various canopy locations. Mean evaporative potentials averaged over 6- to 10-day intervals ranged from 0.00 g H2O h-1 in understory and exposed, interior canopies to 0.40 g H2O h-1 in exposed, exterior canopies. Disease incidence and severity were greater in canopies associated with low levels of evaporative potential.