Q. I live in northern New Mexico (summer highs ~90 and winter lows as cold as -10). I have had this tree for three years. I mulch it heavily in he fall and so far it produces beautiful flowers in the early spring. Now this.....
A. I received both emails. At -10 you are right at the edge of USDA 6 and Western Redbud is recommended for zones 6 to 9. Verticillium wilt is possible. However, this tree is fairly young and it is not common on young trees. It is more common on older trees and less vigorous older growth or very vigorous growth due to over fertilization. Cytospora may be a problem if the tree was damaged during winter cold weather.
Regardless the treatment is the same and that is prune out damaged wood. A good idea anyway. Make sure your pruners are cleaned and sterilized with alcohol, Pine Sol or 5% bleach solution. Oil them afterwards if you use bleach.
With Verticillium wilt the pruned limb should be cut off 12 inches below any signs of wilting. If this is not possible then remove what you can and hope for the best. I am not sure on Redbud but VW can usually be identified on most trees by what is called vascular streaking in the wood where the wilting is occurring. Dead wood you wont see any streaking..it is dead. On some trees like olive the streaking is not visible.
This is a disease found in soils. You should not plant any trees susceptible to VW in that hole. That includes most trees. Ornamental grasses are okay to plant there. Also pines, firs, juniper and spruce.