88 



ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 



Fig. 87. — The sycamore anthracnose fungus frequently spreads from 

 leaves into twigs and branches and forms cankers on the branches around 

 the bases of the diseased twigs. 



The diseased areas on the leaves are small to large, irregular 

 brown areas adjacent to and centering around diseased spots on 

 the midribs and veins (Fig. 88). This type of leaf injury rarely 

 causes conspicuous defoliation. Dark brown fruiting bodies or 

 pustules of the fungus appear on the diseased tissues, especially 

 on the midribs and veins. The pustules can be seen with a hand 

 lens and sometimes with the naked eye. During the summer and 

 fall, the fungus spreads from the diseased areas through the 

 veins, midribs, and petioles into the twigs to which the leaves are 

 attached. It overwinters in the invaded twigs and becomes active 

 the following spring, when it causes twig blight, the first stage 

 described above. 



Severity of anthracnose is related to temperatures prevail- 

 ing during a 2-week period that starts with the first leaf emer- 

 gence in the spring. Severe shoot blight will occur if the average 

 mean daily temperature during this period is between 50 and 55 

 degrees F. Shoot blight decreases as the average mean daily tem- 

 perature increases from 55 to 60 degrees F. Very little if any 

 shoot blight will occur if the average mean daily temperature is 

 above 60 degrees F. Warm periods of a few days with day tem- 

 peratures above 80 degrees F will prevent extensive fungus 

 growth. A limited amount of fungus growth will result in little 

 or no anthracnose. 



