CARTER: THE WETWOOD DISEASE OF ELM 



13 



appearance by the time they fall. Leaves that wilt slowly may 

 turn yellow or brown before they fall. Many of the brown leaves 

 become dry and brittle and remain attached to the affected 

 branches for several weeks (Fig. 13). 



Foliage wilt resulting from toxic wetwood sap spreading 

 into branches has been observed on elm trees as large as 10 inches 

 dbh (diameter at breast height), but most frequently on trees 3 

 to 6 inches dbh. Elms more than 10 inches dbh affected with wet- 



Fig. 14. — Brown streaks produced by wetwood in the younff sapwood of 

 branches, especially in the current-season spring wood, is easily confused 

 with similar brown streaks produced by other wilt diseases of elm. 



wood usually do not wilt but frequently develop yellowing and 

 browning of foliage, followed by leaf drop and branch dieback. 

 General decline may occur in these larger trees affected with 

 wetwood. 



General Decline. — Conspicuous foliage wilt is frequently fol- 

 lowed by dying back of affected branches. This dieback may be 

 limited to only tip portions of branches, or it may include entire 

 branches (Fig. 15). In some trees, very few branches die during 

 a single growing season and the trees recover in succeeding years. 

 In other trees, a few scattered branches die annually and the 

 trees show gradual decline over a period of years. In large, old 

 trees, this gradual decline may be attributed to old age, when ac- 

 tually it is one phase of the wetwood disease. 



