We've pressure washed the area around the trees but the honey dew will come back until it's gets colder and the aphids die off. It is too late in the season to apply a systemic pesticide which is the only product we would use in this application. A foliar application would deposit pesticide on the play structure and we don't want the kids coming into contact with any pesticides. We keep a list of trees that develop aphid problems so that they are treated properly in the Feb-Mar time frame. We'll add these trees to the list.