CARTER: ILLINOIS TREES: THEIR DISEASES 



73 



and for some time after death. Immature leaves curl, droop, 

 turn dark brown to black, and remain attached to the branches. 

 Leaves on wilting bur oak and white oak usually turn light brown 

 or straw color, curl, and remain attached to the branches. 



In trees of the red oak group, brown to black discoloration 

 usually develops in the current-season sapwood of wilting 



Fig. 69. — In trees of the red oak group that are affected with oak wilt, 

 brown to black streaks develop in the young sapwood of wilting branches. 

 The normal white color of healthy sapwood is shown by the branch piece 

 at top of picture. 



branches. This discoloration may appear as streaks or as dif- 

 fused browning of individual wood rings (Fig. 69). Similar sap- 

 wood discoloration has been observed occasionally in wilting bur 

 oak trees. 



Affected trees in the red oak group may wilt and die in 4 to 

 6 weeks, or during a single growing season. Occasionally, large 

 branches of trees infected late in the summer live over winter 

 and produce a few scattered leaves before dying the following 

 spring. Trees of the white oak group usually die slowly over a 

 period of years. 



