31 



and the cambium layer, which is the growing part of the tree just below 

 the bark, should be cut back to form a shelf to which the metal is nailed. 

 It is necessary to have the metal shaped to the opening and care must 

 be taken that it does not overlap the cambium or bark anywhere since 

 then the new wood would work in under and pry it up instead of closing 

 in over it. The open cavity treatment or this modification of it is use- 

 ful for very large cavities and where stress or bending might cause 

 <isj)halt or concrete to crack. 



Aff/ilfilf Filling. The asphalt method is used for openings where little 

 bending occurs or for relatively small holes. The cavity is cleaned out 

 and prepared just as for the open treatment. The mixture used is about 

 one part of asphalt (heated) to six parts of sand or sawdust. This mix- 

 ture is packed in with a trowel behind a metal front. 



dntcreip Filling. The concrete method of filling cavities is restricted 

 to small holes or ones at the base of the tree where there will not be 

 much bending. The preliminary steps are identical with those under- 

 taken before using asphalt. After the walls of the cavity are painted 

 with tar or carbolineum, nails or iron braces are fastened to them to 

 help retain the concrete. It is necessary to have the cavity wedge- 

 shaped, smaller at the mouth than at the back in order to retain the 

 cement properly. (See diagram, page 28.) The filler is one part of 

 Portland cement to three parts of coarse sand or gravel. If the dry 

 method is used then only enough water is added to make the mixture 

 capable of being molded. It must then be packed in solidly and tamped. 

 If the wet method is used a sack or cloth must be nailed .across the mouth 

 of the cavity and the soft concrete filled in behind it. Before the cement 

 has entirely hardened the sack should be taken off and the edges of the 

 cement trimmed back below the cambium. The cement must not be 

 allowed to bulge at the mouth. It should be flat or very slightly convex 

 if the wood is to heal over it properly. A waterproofing concrete paint 

 should be used to exclude moisture from the filler. 



Root rots are caused by disease organisms which spread through the 

 soil and are very difficult to combat. The common cotton root rot and 

 others closely allied may cause large trees to wilt and die within a few 

 hours. There seems to be no practical remedy for such diseases and 

 little or no forewarning that they are present and threaten to do dam- 

 age. \Yhere a tree has .been killed by root rot no other tree should be 

 planted in that location since the disease is in the soil and new trees 

 will almost certainly be attacked. 



Barl- Diseases. Canker and bark diseases are common on poplar and 

 many other trees. All diseased bark and wood should be cut out and 

 the wound treated with creosote. 



Blight . Leaf blight and leaf spot diseases are caused by mildews, and 

 may be controlled by spraying with a good fungicide like Bordeaux mix- 

 ture or lime-sulphur wash. (See page 27.) Bordeaux mixture may be 

 purchased ready made but cannot be made up at home to good advan- 

 tage owing to the rather expensive apparatus needed for preparing it. 

 Raking and burning all fallen leaves will greatly assist in the control 

 of diseases affecting the foliage. 



WKATHKH IX.7TKY 



Dry weather injury can be minimized by frequent cultivation and 

 occasional thorough irrigations, preferably through pipes or tiles sunk 

 around the roots of the trees. 



