Funny about the apple trees. I got PI very badly as a kid, and our whole neighborhood that I grew up in apparently was an apple orchard before it was turned into houses. Had several old trees in the yard. So that makes a whole lotta sense!
A mixture of dawn soap, epsom salt and white vinegar in a large spray container, (found at Lowes, Home Depot, Agway). Will kill poison ivy and most weeds. I don’t know if it will penetrate the ground for any left over runner roots if the leaves are all pulled up. Hope your husband recovers quickly.