Verticillium wilt

Symptoms
Yellowing and shrivelling of lower leave
Some or all of the plant suddenly wilts, especially in hot weather. Plants may recover in cooler or wetter conditions
Brown or black streaks in the tissue under the bark. These are visible as a circle of brown marks, if the stem is cut across transversely. In woody plants the marks are in the outer (most recent) growth ring, although older infections that were not fatal may have left similar marks in older, inner growth rings
Branch dieback is a common symptom in trees and shrubs. Sometimes only part of the plant may wilt and dead branches may indicate infections which occurred in previous years