Woolly apple aphid (WAA) has become more common over the past few years and is a quarantine threat for export to certain countries. WAA can be found feeding on the roots as well as occurring in the tree canopy where it can appear as a white cottony mass on pruning scars or shoots.
The delayed dormant (DD) spray is the first opportunity of the season to control woolly apple aphid. While it has been listed among the many targets of the oil + organophosphate spray at delayed dormant for many years, recent research has confirmed the efficacy of oil + Lorsban at this timing. A delayed dormant application has provided suppression through the summer, and often for the entire season. Suppression is not always complete, but may keep populations below a treatment threshold. In some cases, a large population will build in the fall despite the DD application. Oil alone is not effective for WAA, and so far, substituting other materials for Lorsban has not been effective, either.
(Elizabeth Beers, WSU-TFREC)