Hi Peter,
Nice detail in your post and questions.
Unusual and extreme weather can throw a twist into any orchard on any given year. I think it keeps more orchardists (and farmers, in general) on their toes than any other factor.
Weather anomalies may have set the stage, for you, and I also agree with the mowing being the most likely instigation to moving a variety of insects from the understory around your trees, up into them.
General rule, hold off on the mowing until after petal fall. Next, strongly consider leaving sizable strips or areas of biologically diverse habitat for predator and prey species alike, adjacent to your trees -- think: not more than a stones throw away. Many of the beneficial insects we desire to see most in our orchards, to help with controlling the 'most wanted' outlaws, require nectar sources (as adults) over an extended period that our fruit trees alone can rarely supply.
I understand the desire to isolate a particular plant species for eradication when it appears to be a primary food source for a particular undesirable insect. It is human and we have all been there, with that contemplation, at one time or another. I want to put a plug in for not wiping out the clovers and dandelions as they are highly utilized food sources for native bees & pollinators in my orchard and quite possibly yours too. In some periods of the summer, I can walk around my acreage and often find a solitary bee sitting within each dandelion (and many of the dandelion relatives) bloom --
that just makes me smile. . . . and clover, is not only food for pollinators above ground, but it is also an important food source below ground as well.
Biological diversity (macro & micro) within the orchard will help mitigate extremes . . . seek and encourage balance and you will find the sustainable orchard you are looking for . . . and hopefully more time for you to enjoy the fruits of your labor.
Good luck!
Gopher Hill ApplesZone 8 in California