July 6, 2006 at 7:11 a.m.
Last week a couple came in with three branches of three different large oak trees. They were concerned that it was oak wilt and somewhat relieved when we diagnosed it at oak anthracnose.
Symptoms first appear on newly emerging leaves on the lower branches. These infections produce irregularly shaped spots and blotches that can deform the leaf. Severe infections can result in leaf drop, usually followed by new leaf growth. The fungus is capable of spreading into the twig where it overwinters. Twigs infected during the growing season may often die before their buds are able to open the following spring, causing branch dieback.
This disease is often mistaken for oak wilt which is a much more serious disease. Unlike oak wilt, oak anthracnose is most severe on white oak, whereas oak wilt is most severe on oaks in the red oak family (pointy leafed oaks), and include Northern Red Oak, Pin Oak, and Black Oaks.
Leaves of trees infected with oak wilt develop browning of the leaf margin, and are wilted. Symptoms of Oak Wilt begin in the upper portion of the tree, unlike oak anthracnose which commonly begins in the lower canopy.
Although ugly, oak anthracnose does not cause permanent damage to otherwise healthy trees. Cultural measures to manage this disease include proper watering, mulching, fertilizing and removal of infected material. Raking leaves in the fall and pruning dead and dying branches reduces the number of new infections the following year. Trees should be pruned only during dry weather.
Do not prune oaks in April, May or June. This minimizes the likelihood of attracting the beetles that carry the fungus that cause oak wilt.
Trees that have been defoliated several years in a row, or are newly transplanted, may require chemical interventions next year.
Fungicide application should begin at bud break to protect new growth. Repeat applications according to the fungicide label during cool wet weather. For smaller trees, read the label carefully and apply only as directed. Large trees will require professional assistance to access the special equipment to ensure adequate coverage. Currently, labeled fungicides include Throphanate-Methyl (Cleary' s 3336, Mancozeb, and copper containing fungicides).
It' s almost county fair time! The Master Gardeners will be back in the commercial building this year at the Chicago County Fair in Rush City. Stop by with your gardening questions or to check out the displays. You can also bring samples to be diagnosed or identified.
PLANT CLINICS: Volunteer Master Gardeners will be available Mondays from 4-7 at the Extension Office in North Branch at 38780 Eight Ave. to answer your gardening questions. You can also call 651-674-4417 during these hours to speak with a Master Gardener. Samples can be dropped off during the day on Monday if you cannot stop in during clinic hours. Please note MONDAY is the only day you can drop off samples, as there is no longer staff at the North Branch Office who can answer gardening questions.
VOICE MAIL: You can leave a question for a volunteer Master Gardener at 651-674-4417. Depending on the volume of calls, they try to respond within a couple of days. During office hours ask for the Master Gardener voicemail, after hours, select ext. 18. You can also get your question answered on the web at: www.extension.umn. edu/askmg.