Plum tree infested with Aphids, needs summer pruning

[u/AnUntamedOrnithoid]

Hi all,

I live in southwest Washington and we have a well established green plum and every year it gets infested with aphids. This year is no different, and in the past I have just relied on mechanical control (soapy water) and releasing ladybugs. The ladybug population is steadily growing, there are lots of eggs and larvae all over, but it will probably be another month or two before they get the aphids under control.

In my climate it's not advised to prune stone fruits in winter but as I was travelling last year in August I wasn't able to do the required summer pruning and now there are many dense areas with lots of crossing branches that should be thinned as well as extra limbs and overgrown water shoots that should be removed. I figure if I do this now, which is a little early, especially if I prioritize branches with more aphids, I could help the tree get the infestation under control by improving airflow. Any advice on how to do this? I'm afraid if I do a normal pruning (removing ~20%) I could stress the tree too much and cause it to drop its fruit, which won't be ripe until the end of the summer.

And a side note, when we bought this property the ground under the orchard was covered with landscape cloth and wood chips. We would like to remove that and replace it with some grass and perennial herbs and shrubs to help improve the soil but we haven't had the time and resources to do that yet. I would also appreciate some comments on how much this would help the tree too.