Quantifying the distribution of oak lecanium scale, Parthenolecanium corni Bouché and P. quercifex Fitch, infestations on landscape willow oak (Quercus phellos L.) trees and resultant consequences for tree condition

Lecanium scales, Parthenolecanium corni (Bouché) and P. quercifex (Fitch) are common pests of ornamental oak (Quercus spp.) trees in the eastern United States. It is unclear what lecanium scale densities oaks can tolerate prior to declining in condition. There are no established monitoring guidelines to determine when interventions are necessary to address infestations and improve tree health. We examined the abundance and distribution of lecanium scale in urban and rural Quercus phellos L., and related scale densities to tree condition in Lexington, Kentucky. We hypothesized that scale abundance was greater in the lower canopy, total scale abundance was greater in urban trees compared to rural trees, and counts from formal sampling methods were not different from field inspection methods. We removed eight 30cm twigs from each tree: one from each cardinal direction in the lower and upper canopy from a total of 60 trees. We selected 8 evenly distributed branches from the lower canopy to visually inspect for mature females. We counted females from the terminal bud to 30cm down the branch. We compared scale counts from the upper and lower canopy within each tree, and total scale density between urban and rural trees. In-lab scale counts were compared with counts from visual inspections in the field to test the effectiveness of visual search. We used percentage of canopy dieback to calculate tree conditional ratings and determine the scale density that worsens tree condition. Our results will be used to construct intervention thresholds for lecanium scale in managed landscapes.