General advice.
It should be remembered that after a tree is once attacked and seriously injured by one or more of these wood-boring insects, nothing can be done to repair the damage, and that therefore preven tion is of primary importance. Thus it will be seen that the control of an outbreak of any of the principal insect enemies of the woodlot involves the adoption of methods of management by which the utilization of the infested trees at the proper time will destroy the insects and bring about the desired results with little or no additional expense, and this is to be supplemented by other features in the management which will prevent future trouble.
Some of the rules of general application are as follows : Fell and utilize or destroy, in the fall or winter, all dying or recently dead trees before the broods of destructive enemies have had time to develop and emerge ; utilize or destroy all tops, large branches, and logs from living trees cut the pre vious winter, spring and summer, and burn the brush over the stumps.
Avoid injury of any kind to the bark and wood of living timber, especially of oak and chestnut.
Cut and utilize the old trees which show evi dences of deterioration, and those which have been injured by lightning, storm or other causes ; and if the trees are infested by destructive insects, do the work in the fall and winter.
Forest and Timber Diseases. Figs. 492-497.
The diseases which affect forest trees manifest themselves in various ways, depending on the part of the tree which is attacked. Diseased trees may be recognized by the yellowing or other discolor ation of their leaves, a much reduced growth of the trunk and branches, the dying of the tops, the ap pearance of swellings on leaves or branches, and by the growth on trunks or branches of punks or toadstools. A diseased tree forms less wood than a healthy one, and in many cases decays at the heart, (Fig. 492), with a resultant total destruction of the wood, and ultimate death.
Trees are liable to become diseased from the first year on. They are most liable during the latter part of their life. A number of fungi attack seed ling trees and cause their death, by strangling them or by killing the young leaves. As the trees grow older, the destruction of certain branches and leaves may not have any very serious results ; but after they have reached a period of maturity, they become more subject to disease, because larger branches will be broken off ; and more wounds are made in old trees than in young ones. Practically
all kinds of trees are subject to disease, and some more than others, The redwood, cypress and the various cedars are comparatively free from disease ; so, also, are trees like the red gum, sycamore and sassafras. The oaks, beech, birch and other hard woods are rarely attacked when young, but become very liable to disease after they have reached the age of fifty years or more ; the same is true of pines, firs and spruces.
Causes of disease, and points of attack.
Diseases of forest trees may be due either (1) to unfavorable conditions of soil and climate, or (2) to parasitic enemies, as insects, fungi and higher plants. Wet, soggy soil will produce stag-headed trees; excessive quantities of sulfur gas in the air will result in a discoloration of the foliage of the entire tree, and frequently in its ultimate death. In dry years there will be very much less disease than in years of heavy rainfall. Trees that are grown very close together will be much more subject to disease than those that are farther apart. Wood lots in which all of the trees are of one kind will be much more liable to disease than woodlots in which different kinds of trees are grown. In seed beds, diseases will be favored by poorly drained soil and by excessive mulching. Thrifty trees will always be very much less subject to disease than weak ones.
The diseases due to fungi can be divided into (1) diseases of the living parts, and (2) dis eases of the dead parts. The diseases of the living parts affect the leaves, the younger branches and the smaller roots, and a thin layer of the body of the tree, including the most recently formed wood and the inner bark. The diseases of the dead parts affect the older wood of the trunk, roots and branches, known as the "heart-wood." The fungi that cause disease of the living parts bring about local or general disturbances, which at first weaken the tree and may ultimately kill it ; those that attack the heart-wood bring about the decay of the heart-wood, resulting in the loss of wood, and when the decay goes far enough, in the weakening of the tree so that it is easily broken off.