Specialized columns of wood cells called vessels carry water and nutrients absorbed by roots to other parts of the tree. Fungi inhabiting vessels may produce toxins that cause leaves to turn color and wilt, or they may cause vessels to become plugged. In either case, affeaed branches die if enough vessels are diseased.

Control of most vascular wilt diseases is difficult, but in some cases diseased trees recover if growing conditions are improved by supplemental watering and fertilization.

1) Verticillium wilt
Verticillium dabliae red, slv, sug, nwy, jpn, syc

V. dabliae is a fungus that survives in soil as tiny, seedlike structures called "microsclerotia." These structures can lie dormant for many years until a susceptible root grows close enough to them to stimulate germination. Infection takes place through roots, and from there the fungus enters the vascular system and moves up the stem through vessels. Combined effects of host reaction to V. dabliae and toxic action of V. dabliae itself result in plugging of water conducting vessels and eventual wilt of leaves beyond affected portions. Vigorous trees can limit damage from the pathogen by adding new growth rings with pathogen-free vessels, and such trees have been known to recover. Those that die may take many years to succumb to the disease.

Verticillium wilt can be difficult to diagnose in the field, and laboratory cultures are often required to confirm initial suspicions. At the outset, symptoms are usually confined to one or two branches and may be any of the following: (1) buds fail to open, (2) leaf and twig growth is stunted, (3) leaves have marginal browning (scorch) or are wilted, (4) green or greenish-brown streaks are visible in the outer wood of infected branches (figure on the right). It is often necessary to look for the streaks some distance below the site where leaves are scorched or wilted. If one removes pieces of bark at periodic intervals back to where the affected branch joins the main stem and still sees no stain, V. dabliae is most likely not responsible for the other symptoms. If streaks are found, branch samples 10-20 cm long with stain can be collected and submitted to an appropriate laboratory for further tests. Most land-grant and state universities and some private arborists have laboratories equipped to perform these tests.

Trees infected with V. dabliae have been known to recover if they are watered and fertilized and if diseased branches are removed. This course of action should be followed whenever trees are determined to have Verticillium wilt and pruning will not destroy the value of the tree as a landscape specimen.

2) Sapstreak disease
Ceratocystis coerulescens sug

Sapstreak disease has been found in forests and sugar bushes but not in landscape trees. Little is known about the disease, but it poses a potentially serious threat to sugar maples in the Northeast and Midwest. Insects are presumed to carry spores of the pathogen and to deposit them in fresh wounds on healthy trees. Roots and bases of sugar maples tapped for syrup production are frequently wounded during sap collecting and hauling, and these trees may be especially vulnerable to the disease.

Sapstreak disease, like Verticillium wilt, is difficult to diagnose in the field. Development of small leaves followed by gradual deterioration of tree crowns over several yeas is characteristic of sapstreak. If this is observed, one should cut into several major roots of declining trees to see if a watersoaked, gray to brown stain with reddish fleck or streaks is present in the root wood. (The "sapstreak" stain radiates out from the center of diseased roots in a star-shaped pattern figure on right). If stain is observed, pieces of stained wood should be collected and submitted for laboratory culture.