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Cedar-Apple and Related Rusts

April 14, 1999
The tree rusts of concern to landscapers and homeowners in Illinois are cedar-apple, cedar hawthorn, and cedar-quince rusts. From their names, you can correctly assume that two hosts are necessary for the disease to occur. The chemical options for control center around protecting the apple, hawthorn, or crabapple hosts with a fungicide. If you have worked with these diseases in the past, you know that hawthorns are particularly troubled by cedar-quince rust, which causes stem galls on the hawthorn. Chemical options are listed in the Illinois Homeowners' Guide to Pest Management and the Illinois Commercial Landscape & Turfgrass Pest Management Handbook. Timing is the critical factor.

The cedar host (red cedar) develops galls over the winter. These galls are hard, brown, and about the size of buckeyes with cedar-apple rust, about the size of grapes with cedar-hawthorn rust, and merely roughened stem areas with cedar-quince rust. Chemical companies tell us to spray when the new growth appears and flower buds begin to open. An April 8th report from The Morton Arboretum in the Chicago area states that the galls of cedar-apple and cedar-hawthorn rust are now showing the beginning of telial horns. Now is the time to spray the alternate hosts to protect against spore release from those galls. Hawthorns are generally slower to leaf and flower, so watch hawthorns closely for signs of bud break. Also refer to Report on Plant Disease No. 802, Cedar-Apple and Related Rusts. (Nancy Pataky)

Author: Nancy Pataky


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