CARTER: ILLINOIS TREES: THEIR DISEASES 81 



Fig. 79. — Elongate, depressed Cytospora cankers may girdle and kill 

 affected stems of poplar. 



comes brown and sunken. The fungus produces fruiting bodies 

 which appear as pustules in the diseased bark. Spores of the 

 fungus are produced in these fruiting bodies and under moist 

 conditions they ooze out in slender, threadlike coils. These spores 

 may be splashed by rain or carried by wind, birds, or insects to 

 other trees. 



All dead and dying branches of affected trees should be 

 removed. Trees affected with extensive trunk cankers may be 

 cut and burned, or they may be subjected to careful surgery, fol- 

 lowed by the use of a disinfectant, such as denatured alcohol. 

 Surgery may prolong the lives of some severely affected trees. 

 Wounding of healthy trees should be avoided, since the fungus 

 enters trees through wounds. Trees should be given plant food 

 to maintain vigorous growth, as described in the section "Feed- 

 ing." When it is feasible to do so, the planting of species of pop- 

 lar most susceptible to this disease, such as Simon and Lom- 

 bardy, should be avoided. 



Dothichiza Canker. — This stem disease, caused by the fungus 

 Dothichiza popidea, affects many species of poplar; it is most 

 destructive on Lombardy poplar. It produces oval to enlongate 

 sunken cankers on the twigs, branches, and trunks. In time, the 

 diseased bark turns brown and cracks, and the underlying dark 

 brown diseased wood is exposed. Callus tissues which form at the 

 borders of the cankers tend to grow over the surface of the ex- 

 posed wood. Trunks and branches girdled by cankers die. Young 

 trees usually are killed by the disease. Older trees may not be 

 killed but usually they are disfigured to the extent that they lose 

 their ornamental value. The treatments recommended for trees 

 affected by Cytospora canker usually are effective against this 

 disease. 



Crown Gall. — This stem disease as it affects poplar is de- 

 scribed in the section on willow. 



