Cedar trees in my windbreak are turning brown at the base. I can't find any insects, but it's getting worse every year. What's wrong?
Eastern redcedar, Rocky Mountain juniper, and other junipers planted in Nebraska for ornamental or windbreak use are susceptible to several foliage disease fungi. The most damaging of these is Cercospora blight.
Cercospora blight can be distinguished from other juniper diseases by the pattern of foliage infection and death. Typically, the older foliage in the lower and inside portions of the tree are the first to become infected and die. The disease progresses slowly from the interior of the tree outward and from the lower branches to the younger, higher branches. Severely infected trees may only have green growth on the top half or one-third of the tree. Small shoots and branchlets from the inner tree will often fall from the tree during October and November following infection.
Initial infection occurs during late June and early July. Fungus spores are spread by rain splashes and infect susceptible foliage. Applications of Bordeaux mixture or a liquid copper fungicide such as Tenn-Cop 5E will effectively control this disease. At least two applications are needed for good control. The first application should be made during the first half of June, just prior to initial infection. The second treatment should be made during the last half of July. The second application normally gives good protection against infection for the remainder of the season. However, additional applications may be necessary during periods of frequent rains.
Phomopsis Twig Blight may be confused with Cercospora blight but can easily be distinguished from it by the progress the disease takes through the plant. Phomopsis twig blight first effects the tips of the twigs and progresses back to the main trunk of the tree, while Cercospora spreads from the inside outward and from the bottom of the plant upward. Determining the cause of damage is very important because different chemicals are required for control.
More information:
Diseases of Evergreen Trees, Nebraska Forest Service
Cercospora Blight, University of Illinois Extension