12 



ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 50 



sionally along the margins of leaves (Fig. 12). This symptom 

 appears most frequently during late July and August. Many of 

 the scorched leaves drop prematurely. However, scorch does not 

 result in any noticeable effect on the growth of trees. 



Foliage Wilt. — Wilt of foliage (Fig. 13) occurs on elms af- 

 fected with wetwood when a sufficient quantity of toxic sap that 









Fig. 13. — Wilt caused by wetwood can be distinguished from other elm 

 wilt diseases only by laboratory analysis. 



has accumulated in the trunk wood is carried into the branches. 

 The sap spreads through the current-season spring wood in the 

 branches and produces brown streaks or solid bands of discolora- 

 tion (Fig. 14). Leaves on affected branches curl upward along 

 their margins; then the petioles become flaccid and the leaves 

 droop. Curl and droop are followed by wilt. Some leaves that wilt 

 rapidly drop from the trees while still green. Other leaves that 

 wilt rapidly take on a dull, greenish-brown or somewhat bronzed 



