Archive for Sunday, June 1, 2003

Fungal disease can overtake many trees

June 1, 2003


Although the timely rains have been great for gardening, they also have created an environment for many tree diseases to develop, including Anthracnose. Many trees in Lawrence have sparse canopies or leaves that are drying up and falling off. So, if it looks like fall in your yard this spring, here may be the cause and the cure.

Anthracnose is a fungal disease with several phases. The most obvious disease, shoot blight, can be found on many sycamore trees. The fungus girdles the succulent new stem and causes all of the emerging leaves on the shoot to wilt and die. I have seen trees where up to 90 percent of the developing shoots have been killed. Although the damage looks devastating, sycamores have a remarkable ability to recover. During the next several weeks, new shoots will appear. These shoots should not be blighted as warmer weather is not favorable for Anthracnose development. By mid- to late June, trees should be fully leafed out, and in most cases, you will not know the tree had a problem.

Sycamores are not the only victims of this disease. Anthracnose-type diseases also are being found on a number of trees. Ash Anthracnose is causing blotches at the leaf margins of many Ash trees. Maple Anthracnose can be seen as small dark brown to black spots on silver and sugar maples. These spots usually are associated with leaf veins and may coalesce to form larger streaks or blotches on the leaves.

Elm black spot, sometimes referred to as Anthracnose, occurs on most elms, but it is most severe on Siberian and Chinese elms. Small yellow spots initially develop on the upper leaf surface. On susceptible elms, the spots may enlarge and blight entire leaves and succulent shoot growth.

Anthracnose is a seasonal disease. Fungicides can be applied to newly developing shoots in the spring, but this is difficult to do on large trees, so it is rarely done. The fungicides Alamo and Arbotect can be injected into trees in the fall to help protect against spring infection. However, this treatment should only be considered for specimen trees or those that have suffered perennially from the disease. Spraying or injecting trees at this time will do no good. All of these diseases subside with the onset of hot weather, so fungicide applications are not needed.

Simply clean up the fallen leaves and watch the new, healthy, leaves begin to emerge.

-- Bruce Chladny is horticulture agent at K-State Research and Extension-Douglas County. For more information, call him at 843-7058 from 8 a.m. to 5 p.m. weekdays.

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