Excerpt from the report Introduction: Tree diseases take a heavy annual toll of timber from forests and farm woodlands. Much of this loss is preventable. In the United States as a whole, diseases ruin each year 40 percent as much timber as is cut. Many diseases kill trees or reduce their growth rate, but the major loss to the forest results from those that cause standing timber to decay or otherwise become defective. Trees decaying faster than they are putting on new wood, or so defective they will never produce a usable product, are liabilities rather than assets in the farm woods or forest. The space such trees occupy remains unproductive until they are removed. Much disease damage, such as that caused by rots, does not become evident until timber is cut, and then it is too often accepted as inevitable. Bark diseases that appear as open wounds or cankers on the trunk are often regarded as merely mechanical injuries. Blister rust may be easily overlooked as the cause of death of young white pines. To appraise these losses, it is first necessary to recognize them. To prevent them, the factors that lead to them must be known.