WSU Extension


Oak : Oak leaf phylloxera
(revision date: 2/14/2019)

The oak leaf phylloxera is a pest of growing importance in the Pacific Northwest. It’s believed to have come from Europe in the early 1960’s. It is is a yellowish orange homopteran related to aphids and is about 1mm long (less than 1/16 of an inch) and like its aphid relatives it has several generations each year. It is a sucking pest that causes chlorotic mottling. At first the damage is seen as yellowish spots in spring and early summer. Gradually the damage becomes overwhelming and browning and defoliation occurs in late summer. Some trees may produce a second set of leaves after complete defoliation in August, but this severely weakens the trees and some will die. The oak leaf phylloxera attacks mainly Garry oak and English oak. However, other species such as pin oak have also been attacked. Canadian researchers expect that 10% of the trees that are susceptible will eventually die from continuous defoliation. Resident natural enemies will feed on this pest, but are currently not suppressing it to acceptable levels.
Management Options

Non-Chemical Management
  • Natural enemies are important in managing oak phylloxera. Avoid use of broad-spectrum insecticides which kill beneficial insects.
Select non-chemical management options as your first choice!

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Hi-Yield Dormant Spray
    Active ingredient: oil/pet distillate  |  EPA reg no: 7401-428
  • Safer Brand Insect Killing Soap Conc II [Organic]
    Active ingredient: potassium laurate  |  EPA reg no: 42697-60
  • This list may not include all products registered for this use.
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Caption: Oak leaf phylloxera damage
Photo by: A. Antonelli