Vascular Wilts
Vascular Wilts
The term ‘wilt’ is used to describe a condition in which leaves lose turgidity from a lack of water and become limp or flaccid. There are many causes of wilting and as a result this type of symptom can lead to confusion and misdiagnosis. Therefore, care must be taken in identifying a problem based solely on wilt symptoms. For example, physical injuries to roots, trunk and stems, or localized bark injury caused cankers, blighting and insect feeding may create wounds that impede water movement and result in wilting. In these situations, wilting is secondary to and often removed from the primary, localized damage. In other cases, environmental stresses such as drought or heat may cause wilting that can be reversed following alleviation of the stress (e.g. the tree is watered). True vascular wilt diseases are relatively uncommon and are caused by pathogens that systemically invade and plug the vascular system (xylem)by physical and/or physiological processes. Wood in annual rings nearest the bark is sometimes discolored and can be a useful diagnostic feature associated with vascular wilts. However, deep, radial staining patterns in wood may be a result of wound reactions of the tree to an unrelated injury or by growth of non-wilt inducing bacteria and fungi. An example would be "blue" stain fungi that live in the ray parenchyma cells and are usually associated with various bark beetles.
In most, but not all cases, damage caused by vascular pathogens is irreversible. Thus, most of the true vascular diseases are lethal. This section covers only those diseases caused by vascular wilt pathogens; wilts associated with abiotic causes or localized damage are discussed elsewhere in this publication.
Diagnostic Hints: Wilting of leaves is the main symptom of wilt diseases but terminal dieback and decline is also common.
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