66 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 



though it occurs on many maples each year, it does not cause 

 affected trees to die. 



Canker and Dieback. — Canker and dieback of twigs and 

 branches on maples have been associated with several fungi in 

 Illinois : Steganosporium qnriforme on hard maple and Norway 

 maple, Nectria ciyinabarina on sycamore maple, and Sphaer op- 

 sis 7iegundinis, Leptothijrium maximum, and Phacidium negun- 

 dinis on box elder. These fungi attack weakened trees and kill 

 twigs and small branches. Occasionally they develop on large 

 dying branches. Affected trees should be given plant food to 

 stimulate growth, and all affected branches should be removed. 



Verticillium Wilt. — This wilt, caused by Verticilliimi albo- 

 atruTYi, is known to affect 16 species of maple in the United States. 

 Other trees affected by this disease include almond, ash, black 

 locust, catalpa, elm, goldenrain tree, linden, magnolia, pagoda 

 tree, redbud, Spanish chestnut, tulip tree, tupelo, and yellow- 

 wood. 



Foliage of trees affected by this disease may wilt at any time 

 during the growing season. However, on most affected trees, the 

 foliage wilts in late June or in July or August. Wilt may occur 

 on only a few branches, on whole sections, or on all branches 

 of a tree (Fig. 40) ; in the last case, the tree usually dies very 

 soon. Some trees that show a limited amount of wilt may recover 

 and not show wilt in succeeding years. In maple, Verticillium. 

 produces fine green streaks in the young sapwood of wilting 

 branches, especially in sapwood of the current season (Fig. 62). 

 In other kinds of trees, Verticillium produces brown to yellowish- 

 brown streaks in the young sapwood of wilting branches. Since 

 the fungus can live in the soil and invade the trees through the 

 roots, the streaks in the sapwood spread from the roots up 

 through the trunks and into the branches. The basal portions of 

 branches showing wilt should be examined for the streaks, since 

 these streaks may not extend to the tips of affected branches. 



Affected trees should be given plant food to stimulate vig- 

 orous growth, as described in the section "Feeding." All dead 

 branches or dead wood on branches showing wilt should be re- 

 moved. However, it is advisable not to remove live branches or 

 twigs on which the leaves are wilting or have recently wilted. 

 Many branches that show wilt may not die but may produce a 

 new crop of leaves 3 or 4 weeks after wilt has occurred or by the 

 following spring. Pruning will not eliminate fungus that is 

 present in the trunks and roots of affected trees. 



