CARTER: ILLINOIS TREES: THEIR DISEASES 



69 



have been severely weakened by anthraenose over a period of 

 years should be given plant food to stimulate growth, as de- 

 scribed in the section "Feeding." 



Leaf Blister. — Leaf blister or leaf curl, caused by the fungus 

 Taphriua caerulesceus, affects the various species of oak. Red 

 oak is especially susceptible. Usually the disease appears only 



Fig. 64. — Anthraenose of white oak kills irregular areas of tissue along 

 midribs and veins. The light brown killed areas contrast sharply with the 

 green color of the adjacent living tissues. 



during cool, wet springs. Affected leaves show circular, raised, 

 wrinkled, yellowish areas on their upper surfaces; the diseased 

 areas appear as depressions on the lower surfaces of the leaves. 

 Leaf blister seldom causes serious damage. It can be controlled 

 by a spray of lime sulfur or of Bordeaux mixture (copper sulfate 

 and hydrated lime), page 26. One spray applied before the buds 

 open in the spring is recommended. 



Rust. — Leaf rust, caused by the fungus Cronartium quer- 

 cuum, occurs infrequently on oak in Illinois. It produces small 

 yellowish spots with brown, bristle-like tendrils on the under- 

 sides of leaves. Usually it causes insufficient damage on oak to 

 warrant control treatment. Several species of pine are the alter- 

 nate hosts of this rust. 



