Minnesota Plant Diseases. 237 



air to prevent dry rot. Other accessory cautions are also ad- 

 visable and will be mentioned in the discussion of the true dry 

 rot of timbers. Timbers in mines, tunnels and railroad ties suf- 

 fer especially severe depreciations from fungi of this class. 



Prevention. As to the prevention of the ravages of wound 

 parasites of this group, an avoidance of wounds is first of all 

 advisable. Of course this is impossible in forest culture but in 

 shade trees it is practicable. \Yhere trees are pruned the cut 

 surfaces should be carefully covered with creosote or some simi- 

 lar substance to prevent the entrance of spores and their germi- 

 nation. Fall and winter are preferable for this pruning since 

 the absorption of the creosote is more complete at that time 

 than in the spring or summer and the exclusion of the fungus 

 threads is therefore more complete. In the second place the 

 fruiting bodies of all disease-causing fungi should be removed 

 as soon as discovered and burned immediately to destroy all of 

 the spores. This is a prevention against the further spread of 

 the disease. Badly infected trees should in most cases also be 

 removed and thoroughly seasoned or used for firewood. 

 Where the fungus is a root parasite traveling from root to root, 

 as is known to be the case in a few forms, a trench is dug 

 around the infected trees and all roots severed so as to prevent 

 the spread to other trees. The isolated trees are carefully 

 watched and the fruiting bodies destroyed as soon as they ap- 

 pear. Many valuable shade trees are annually lost as a direct 

 or indirect result of timber diseases and such a loss can be almost 

 entirely averted by careful attention as indicated above. 



In forest culture dead trees should be immediatly cut and 

 harvested. This saves the available timber and gives it no chance 

 for deterioration which is sure to set in if the timber is left 

 standing. Such treatment also prevents the formation of fun- 

 gus fruiting bodies, which would spread disease to standing 

 trees. There is an age at which trees may be said to become 

 mature and at this age the natural forces of recuperation just 

 balance the external destructive influences. This age varies in 

 different trees. At this time the tree should be harvested, for 

 in every succeeding year the chances of destruction by fungus 

 pests increase and the tree loses in value. 



