128 FA.EM FORESTRY 



of trees should not be allowed to run through the woodlot 

 and grazing animals should be excluded. Trees and limbs 

 attacked by the chestnut bark disease or other diseases should 

 be cut and the bark removed and burned. This will often 

 prevent the spread of the disease to other portions of the 

 tree or to other trees. Healthy, vigorously growing trees are 

 less apt to be attacked by rot because new wood closes over 

 wounds quickly. Anything that tends to induce health and 

 vigor in the trees will help to prevent decay. 



Insects. — Insects are another cause of damage and often 

 of great loss to the woodlot. Every tree has its insect enemies 

 that live and prey on it every year. Ordinarily they do but 

 little damage. It is only when an insect becomes very numer- 

 ous and it begins to do considerable damage that our attention 

 is called to it. The destruction of birds is said to have been 

 one of the chief causes of the increase in insect pests in recent 

 years. So numerous have the insect pests of trees become in 

 some regions that trees can be grown only by constantly fight- 

 ing their insect enemies, by spraying the leaves with poison, 

 destroying the eggs of insects, burning their nests, and in 

 other ways. 



Insects kill trees by defoliating them or eating the leaves, 

 by sucking the juices through the leaves or bark, or by gird- 

 ling the inner living bark. Some insects live only in the dead 

 wood or heartwood of a tree or only on dead trees, while 

 others attack only living trees. Some live only on one tree 

 or a few trees, while others live on many kinds. 



It is only by becoming acquainted with the life history 

 of insects that they can be combated intelligently and success- 

 fully. Insects that spend the winter in webs in the trees like 

 the brown tail moth or fall web worm can be destroyed by 

 cutting off the webs and burning them or by burning the webs 

 with a long-handled torch. Each web of the brown tail 

 moth will contain from 500 to 900 caterpillars. The gipsy 

 moth lays its eggs in yellowish clusters in crevices in the bark. 



