Orange spots may indicate rust disease which is a fungal infection encouraged by poor air circulation. The shade from the tree should be fine as hostas like shade. Perhaps if you sent a photo I could make a better diagnosis. Giving room around the hosta will help with air circulation. Improve the drainage by adding organic matter to the soil and loosening the soil around the roots. You can give the hosta a fresh start by cutting the infected plants back to the ground and see if the new growth if free of the spots. Keep growing, Marianne Binetti