Weeds with yellow flowers and apple trees
Your weed is yellow woodsorrel. Here is information, including control methods: https://extension.umd.edu/hgic/oxalis-yellow-woodsorrel
Your apple trees may have gotten a severe infestation of apple scab or cedar apple rust. Rust has been defoliating apple trees this year. These are fungal diseases. Fungal disease pressure has been very high this year because of all the rain. Search these diseases on our website for control help.
On the other hand, we cannot say for sure that this is the problem. It could be a number of other things. Please let us know if there are any other symptoms and possibly send photos next year when symptoms first appear.