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Illinois Natural History Survey Bulletin 



Vol. 23, Art. 4 



trees show gradual decline, as in the elm appearance by the time they fall. Leaves 



pictured in fig. 14. that wilt slowly may turn yellow or brown 



Heartwood in the basal portions of some before they fall. Many of the brown 



branches, especially large branches, is dis- leaves may remain on the affected branches 



colored brown, as in wetwood-affected for several weeks. Leaves on some trees 





Fig. 15. — The wilt which occurs sometimes in elms affected with wetwood is evident on 

 branches at right. 



heartwood of the trunk shown in fig. 2. 

 This discoloration in branch heartwood is 

 a continuation of the wetwood-affected 

 heartwood in the trunk. 



Foliage Pathology 



Wilt occurs on elms affected with wet- 

 wood when sufficient quantities of the 

 toxic sap that has accumulated in the 

 trunk wood is carried into the branches. 

 First, affected leaves curl upward along 

 their margins, then the petioles become 

 flaccid and finally the leaves droop. Curl 

 and droop are followed by wilt, fig. 15. 

 Some leaves that wilt rapidly may drop 

 from the trees while still green. Other 

 leaves that wilt rapidly may take on a 

 dull, greenish brown or somewhat bronzed 



may droop and turn yellow but not wilt,; 

 while those on others may turn dull' 

 greenish brown between the veins, fig. 16. 

 Many leaves that turn j^ellow or dull 

 greenish brown may abscise prematurely 

 during July and August. 



Wilting as the result of wetwood in 

 the trunk has been observed on trees asi 

 much as 10 inches d. b. h., but most fre-' 

 quently on trees 3 to 6 inches d. b. h. 

 Elms more than 10 inches d. b. h. affected 

 with wetwood usually do not wilt but 

 frequently develop yellowing and brown- 

 ing of the foliage, followed by leaf drop: 

 and branch dieback. General decline may 

 occur in these larger trees affected with 

 wetwood. 



Many large elms affected with wetwood 

 are characterized by the dying, year after 



