m NEBRASKA STATE HORTICULTURAL SOCIETY 



and shows a fair degree of success. In many cases the disease seems 

 to be entirely under control while in other cases it goes on developing 

 beneath the cover. This may be due to one of three causes: First, the 

 cut was not deep enough to remove all infected wood; second, the sterili- 

 zation was not thorough; or third, the wound was reinfected through the 

 cover not being impervious. 



Corrosive sublimate, solutions of copper sulphate, and formaldehyde 

 are perhaps the best disinfectants. 



Tbe greatest difficulty is found in securing proper material for the 

 cover. It must be of such a nalure that it can readily be applied at the 

 season of the year when pruning is done and must form an impervious 

 layer over the treated surface. It must adhere closely, and not crack 

 or become soft and run off. 



White lead has been extensively used, but proves unsatisfactory for 

 large surfaces for the reason that it can not be applied in a large enough 

 quantity to prevent checking of the wood. Of the numerous materials 

 which have been used, perhaps coal tar, gas tar, pitch and asphaltum 

 are most satisfactory. Coal tar contains some volatile substance, which 

 may be absorbed by the trees and may be a possible source of danger 

 to healthy growth. Gas tar has a tendency to be completely absorbed, 

 and for this reason it may be necessary to renew the application In 

 order to secure sufficient covering. Asphaltum, melted and applied 

 hot, is perhaps the best covering for large surfaces though the disad- 

 vantage of heating before using is great. For this purpose some kind 

 of portable stove is necessary. At ihe Nebraska station we use a tin- 

 ner's gasoline stove. The asphaltum may be melted over a hot fire and 

 kept warm in the orchard by using the small portable stove. 



Liquid asphaltum is easily applied, but has the drawback of con- 

 taining some volatile substance, used as a solvent, which may be ab- 

 sorbed by the wood. 



In general practice it is best to remove any diseased limbs entirely 

 unless the canker is young. Sometimes, however, the removal of the 

 limb throws the tree 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 

 all cases enough wood must be left to support (he weight of the limb and 

 enough sound bark to conduct plant food. The canker may extend down 

 a limb and into the trunk. Where this is the case it is best to take out 

 the tree below the ground, unless the tree is healthy and vigorous other- 

 wise. If the tree is strong or of a rare and valuable variety, it may be 

 treated by removing the infected wood of both limb and trunk and treat- 

 ing the wound. At this station, where a large wound is made in the 

 trunk of a tree, we fill it, after disinfecting, with cement reinforced with 

 wire netting, and cover the whole with asphaltum or tar. All wounds 

 should be made an smooth as possible. I find a pruning saw, a small 



