CARTER: ILLINOIS TREES: THEIR DISEASES 



65 



years may need feeding to stimulate vigorous growth and spray- 

 ing with organic mercury or copper fungicide to prevent infec- 

 tion (Table 1). Two applications of spray at 10- to 14-day inter- 

 vals should give effective control. The first spray should be ap- 

 plied when the leaves are about half grown. 



Tar Spot. — Soft maple is most frequently affected by this 

 leaf disease, caused by the fungus Rhijtisma acerinum. Hard 

 maple and red maple are affected only occasionally. The disease 

 appears first as yellowish-green diseased areas on the upper sur- 



Fig. 61. — Tar spot of soft maple is conspicuous because of the black, 

 glossy, raised, tarlike spots produced on the upper surfaces of affected leaves. 



faces of leaves. These areas, which are oval to irregular in shape, 

 enlarge and become tarlike, thickened, and raised (Fig. 61). The 

 fungus lives over winter in the tarlike spots on fallen leaves and 

 produces spores which, when released during May and June, in- 

 fect the new crop of young leaves. Tar spot can be controlled if 

 infected leaves are raked and burned in the fall, and the new 

 crop of leaves the following spring are sprayed with an organic 

 mercury or copper fungicide (Table 1). One spray should be ap- 

 plied in early May, and, in unusually wet seasons, a second spray 

 should be applied 3 weeks after the first. 



Scorch. — Foliage scorch is a common leaf disease on Norway 

 maple and hard maple during June, July, and August. This dis- 

 ease (Fig. 14) is described in the section "Leaf Diseases." Al- 



