Wilts
Wilting is due to a deficiency of water in the foliage. Death of the foliage and sometimes the shoots, large branches, or the whole tree or shrub usually follows. Drought may not be the only cause of wilt. Several disease conditions, for example, root rots can also cause wilting.
With the diseases called "vascular wilts", wilting occurs because a fungus plugs up the internal water conducting tissues to the plant
To determine the cause of wilting in your plant, examine the soil moisture. Is the soil very wet?
Excess soil water often causes root rot followed by wilting. Examine small roots for rot, which will appear as a black discoloration and a softness of the outer root tissue. If you gently pull on a rotted root, the external skin should separate entirely from it's internal tissue. If the soil is adequately moist and roots appear normal, the plant may have a vascular wilt disease.
Vascular wilts.
Symptoms:
Vascular wilts cause wilting, withering and death of foliage of trees and shrubs, as well as death of shoots and branches or entire plants. Cut diagonally into the wood of an affected branch and look for sapwood discoloured in the growth ring. The discolouration is usually dark green to brown and may be in streaks. The discoloured sapwood is the diagnostic symptom of the vascular wilt disease.
Cause:
Several fungi cause wilts. They act by plugging up the water and food conduction vessels (xylem and phloem) in the plant and restricting the flow of water to the leaves. Branches with wilt symptoms generally die. Some plants die quickly of wilts; others can survive for years, finally losing major branches. The discoloured sapwood is the result of wound gums and chemicals formed by the plant in an attempt to stop the fungal infection. A vigorous plant can sometimes lock up the fungal infection in the annual growth ring of wood, then form an uninfected ring of sapwood during the following year's growth. Maple and Russian olive trees in vigorous health often escape Verticillium wilt infections in this manner, while a stressed tree will lose major branches or die outright.