I'm sorry to hear that your beautiful trees are ailing. There are so many variables to tree problems. What makes you think it's the roots? Here are a few tips: the soil around the tree needs to have both good aeration and good water penetration/drainage. This insures that the tree receives proper hydration and nutrients without causing root rot and disease from an anaerobic environment. Trees also benefit from deep, less frequent watering to supplement rainfall. Tree root diseases often cause vascular problems which prevent the uptake of nutrients, so diseased trees usually end up needing to be removed over time. Weakened trees also become targets of insects which furthur compromise the chances of recovery. If you can find an arborist in your area, I'd recommend you have him take a look. Good luck to you!