2.06 NEBRASKA STATE HORTICULTURAL SOCIETY 



a limb, especially if it is a large one. At first the diseased area 

 may be comparatively small, but it gradually extends farther and 

 farther up and down the branch, as well as around it. I have observed 

 these cankers extending down one side of a large limb and the trunk 

 to the ground and affecting the roots. A peculiarity of this disease 

 is that only a small area of the bark at the point of Infection may be 

 affected but the mycelium goes deep into the heartwood and travels 

 both up and down the limb, coming to the surface again some dis- 

 tance away, especially if the limb is injured at some other point. 

 The progress of the disease in the wood is marked by a dark brown dis- 

 coloration of the fibers. It is this rapid growth in the heartwood which 

 makes it so difficult to control. 



In treating trees for canker we must divide them into three 

 classes. First, those which may be cured profitably by treating. In 

 this case we have trees with all degrees of infection, from a small 

 cankered spot on one limb up to several large cankers on one or 

 more limbs. 



In general practice it is best to remove any diseased limbs 

 entirely, unless the infections are recent. Sometimes, however, the 

 removal of the limb throws the trees greatly out of balance, or, as is 

 often the case, the cankered limb is on the south side, where its 

 removal would expose the trunk and large limbs to direct sunlight. 

 In such cases it is well to try to treat and save the limb unless the 

 disease has progressed too far. 



In treating the limb the cankered and discolored bark and wood 

 must all be removed. It is safest to cut back behind the cankered 

 spot at least one inch into clean growing bark. The wound must be 

 made pointed both above and below because if left square a wedge- 

 shaped piece of dead bark will result which will encourage a new infec- 

 tion. After removing the canker and making a good smooth cut the 

 wound should be disinfected and covered. 



Another important step in treating the canker is to cut the 

 trees back heavily and force out an abundance of new growth. Trees 

 with heavy tops compared to the root systems, or those which have 

 been weakened by any cause, such as drought suffer most severely 

 from Illinois canker. Cutting back the top so that the roots can 

 supply water and plant food in abundance to the remainder, goes a 

 long way towards correcting the trouble. 



The second class of trees are those which are so badlly cankered 

 that it would be unprofitable to try to cure them, but which will still 

 bear a profitable crop of apples. This is the most dangerous class 

 of all for the lay man sees no reason why he should sacrifice a tree 

 so long as it will bear fruit, and leaves it in his orchard to scatter 

 millions of spores to his sound trees. We do not recommend that 

 these trees be cut down but that they be prevented from scattering 

 the disease. This can easily be done by cutting away and burning 

 the dead limbs and by keeping the cankered surfaces of what are 



