Diagnosing Plant Diseases – Part III of IV– Vascular
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By Agnes Farside
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In Part I and II of Diagnosing Plant Diseases I covered a few diseases that can be identified from observing plant leaves, trunks, branches, and stems. Although it was not an exhaustive list, it covered the more common diseases found in the area I live, the Midwest. Part III covers diseases, hosts, symptoms, and controls found through the observation of vascular system of plants. (This is not an exhaustive list.)
Oak Wilt
Oak Wilt is a fungus that infects oak trees and the symptoms vary depending on the type of oak. For oak trees that fall in the Red Oak group (red, pin, scarlet, black, and shingle), discoloration and wilt of the top leaves and lateral branches are the first signs of Oak Wilt. The disease gradually works its way downward until the entire tree is affected. Older leaves may stiffen, while young leaves curl slightly and turn dull green or tan at the edges. Some oaks such as the black and red, my wilt after only four weeks when symptoms first appear and are never able to recover.
This disease turns leaves tan to light brown starting at the tip down to the base of the leaf on trees belonging to the White Oak group, which includes bur, swamp, white, and chinquapin. Vascular discoloration may not be as noticeable in this oak group as the infection is often scattered about the tree. However, if the tree is severely infected, it could die within one year.
Oak Wilt can be carried by insects that feed on the trees sap and through root grafts. In addition, contaminated tools can spread the disease. To control Oak Wilt, prune affected areas from the tree when sap is not flowing or remove infected trees completely, including the roots. As this fungus can produce spores on dead wood, do not use pruned branches for firewood.
Dutch Elm
Dutch Elm Disease is a fungus that infects elm trees, especially the American elm. Branches may die and leaves curl and wilt turning to shades of yellow and then brown. They can fall from a whole branch or portions of a branch. If an American elm becomes infected in spring, it can be dead by the time fall arrives. The only way to identify Dutch Elm Disease is through laboratory testing from samples taken from brown discolored areas just under the bark. The fungus spreads through root grafts, the elm bark beetles, and contaminated tools. To control Dutch Elm Disease, practice good sanitation by quickly removing dead elms, remove diseased root grafts, and control elm bark beetles.
Pine Wilt
Any variety of pine trees, that grows east of the Rocky Mountains, except for white pine, can be infected by this disease, which is caused from pinewood nematodes. Decline in health or even death of the tree are the first signs of Pine Wilt. Needles turn from gray-green to yellow to brown all over the tree and death is usually in later summer to late fall. Some larger species of pine have limbs that die one at a time instead of an overall decline, causing death to be prolonged over a year or more. To control this disease, remove and destroy infected trees and sanitize all pruning tools. There is not chemical control for this disease.
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Author Bio Box: Agnes Farside
 http://www.associatedcontent.com/user/110407/agnes_farside.html
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