ILLINOIS TREES: SELECTION. PLANTING, AND CARE 113 



effectively controlled by applying an organic mercury fungicide 

 at the time the buds are swelling. 



Thousands of London plane trees in the Atlantic Coast re- 

 gion from Philadelphia to Washington, D. C. have been killed by 

 a fungus disease called canker stain. This disease occurs princi- 

 pally in the eastern and southern parts of the United States. 

 Although it was reported affecting dozens of trees in St. Louis 

 in 1947, it has not been found in Illinois. The fungus produces 

 cankers on branches and trunks, and seriously affected trees 

 are killed. To control this disease, special care is required in 

 treating or removing diseased trees and in protecting healthy 

 trees. Information on the procedures to follow should be ob- 

 tained from a plant pathologist. This disease also has been re- 

 ported on sycamore, which appears to be much less susceptible 

 than London plane tree. 



Many London plane trees in Illinois show extensive trunk 

 splitting (Fig, 10) when temperatures are quite low during the 

 winter months. These splits or cracks are referred to as frost 

 cracks. They may measure up to several inches across and sev- 

 eral feet long, and they may penetrate the trunks only a few 

 inches or to the center of the heartwood. Usually these cracks 

 close in the spring and callus forms over them during the growing 

 season. Callused-over, shallow^ cracks may not open in succeeding 

 winters. However, deep cracks usually reopen winter after win- 

 ter. 



Tree of Heaven 



Tree of heaven, (Ailanthus altissima) (Fig. 102) , introduced 

 from China, grows rapidly and may reach a height of 50-60 feet. 

 It is recommended for planting in industrial and other areas 

 where other trees do not thrive. However, it is not desirable for 

 lawn, park, and parkway plantings because it spreads rapidly 

 by root suckers and by seed. 



The alternate, large, plumelike, compound leaves (Fig. 102 

 inset) measure 1-3 feet long and are composed of 11-41 short- 

 stalked, broadly lance-shaped, 3- to 5-inch-long leaflets that are 

 bright green above and paler below. Each leaflet has two to 

 four coarse teeth at its base. The yellowish-green, 14-inch-long 

 flowers, produced in June, form upright clusters a foot or more 

 in length. The male flowers give off a disagreeable odor. They 

 may be borne on the same trees that bear female flowers, or on 

 separate trees. Large clusters of brilliantly colored, winged 



