CARTER: ILLINOIS TREES: THEIR DISEASES 39 



Cankers. — Three fungi, Phijsalospora obtusa, Cytospora sp., 

 and Phomopsis sp., cause canker diseases of ash. Frequently, 

 these fungi attack the trunks and branches of weakened trees 

 and cause severe damage. Healthy trees usually are not affected 

 by them. Dying of portions of branches, of entire branches, or 

 of entire sections of affected trees may be an indication of canker 

 disease. Affected trees may be saved if given food and water to 

 stimulate more vigorous growth in early stages of the disease. 

 Affected branches should be removed and burned. The diseased 

 portion of an affected branch is indicated by discolored or dead 

 bark or by streaks in the wood, especially in the current-season 

 wood. 



White Mottled Rot. — This disease, caused by the fungus 

 Fomes fraxinophilus, is a white mottled rot of the heartwood of 

 both green ash and white ash. It affects the trunks of mature 

 trees and dead trees. In early stages of the disease, small areas of 

 the wood of affected trees are discolored brown. White spots soon 

 appear in the discolored wood. In advanced stages of the disease 

 the affected wood is soft, crumbly, and straw colored, mottled 

 with white. 



The fungus produces large, woody, perennial, hoof-shaped 

 fruiting bodies or conks on trunks of affected trees (Fig. 26). 

 The typical conk, up to 1 foot or more in width, is dark brown or 

 black on the upper surface and straw-colored on the under sur- 

 face. The fungus enters the trees through stubs left by the break- 

 ing off of dead branches and through wounds of various kinds. 

 All dead and dying branches should be carefully removed in such 

 a way as to prevent further infection, and all wounds should be 

 protected with a wound dressing, as described in the section 

 "Wound Treatment." Additional applications of wound dressing 

 may be needed annually. 



BIRCH 



Birch trees weakened by infestations of bronzed birch borer 

 or by unfavorable environmental conditions frequently are at- 

 tacked by canker-producing fungi. 



Cankers. — Several fungi, Cytospora amhiens (Valsa am- 

 biens), Melanconium betulinum, Nectria ditissima, N. cinnaba- 

 rina, Sphaeropsis alnicola, and Valsa betuUna, may cause cankers 

 on trunks and branches of birch trees. Melanconium canker oc- 

 curs most frequently and may contribute to the death of indi- 

 vidual branches or entire trees. 



