My Bradford Pear, Lavender, Willow trees are dying, no drought conditions present, why are they dying?

I see no sign of disease, plenty of rain in addition to regular irrigation, only insects I see are carpenter ants. What could be killing my trees? I have lost two Bradford's and another is stressed. I also have a stressed Lavender tree and a stressed Willow tree, all trees are a little over 10 years old.