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John Fulton

John Fulton
Former County Extension Director

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In The Backyard

Horticulture columns and tips done on a timely basis
verticillium wilt

Verticillium Wilt of Shade Trees

Posted by John Fulton -

Many major tree diseases cause vascular system blockage. Verticillium wilt, oak wilt, and most of the canker diseases fall into the group. Usually a fungus "plugs the pipes" so there is reduced movement of water up and food down. This leads to dead areas above the blockage. Of course, if the blockage is on the main trunk you end up with a dead tree. It is often possible to see streaking of the wood, or a dark ring around the center portion of the branch or trunk with verticillium wilt, but a lab analysis is needed for definite confirmation. There are no cures for any of these diseases at this time, but pruning out infected limbs is practiced. Severely infected trees should be removed to help prevent transfer from root grafting. The list of trees affected by verticillium is very large, but good quality maples are very susceptible. There have been many affected trees again this year, including maples and ashes, as well as shrubs such as smoke bush and viburnam. The only treatment is to water and fertilize to try and get new growth, and new water and food carrying tissues.

The years of stressful weather just keep piling on. Even last year was stressful with an overabundance of water early, followed by the extremely dry period later. Just like us, trees like moderate weather. When we have extreme heat and cold, and no moisture or a flood, the trees are stressed. This stress makes them more susceptible to things that are always in the environment. Try to even out some of the extremes by watering when it is dry, fertilizing when you do the lawn (or just fertilize the tree), and mulching to even out the soil temperature in the root area. Remember that many diseases can be passed with pruning equipment, so disinfect your equipment between cuts.

The following is a recommendation from the University of Illinois Plant Clinic: "Once a plant has succumbed to Verticillium wilt, we recommend replanting that area with non-susceptible species. Apple, pear, crabapple, gingko, sycamore, walnut, willow, rhododendron and azalea, and oaks in the white oak group are some woody plants that are considered non-susceptible to Verticillium wilt. In addition, all conifers are considered resistant to Verticillium wilt.

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