444 



deficiencies, and injury from gases, 



smoke, and fumes. 



FUNGI cause most of the major losses 

 from disease in forest trees and are the 

 chief destroyers or deteriorating agents 

 of forest products. They produce leaf 

 spots and defoliation, wilts, blights, 

 cankers, galls, heart rots, and root dis- 

 eases. Trees that are weakened by fungi 

 often are more susceptible to wind- 

 throw and to attack by insects. In 

 forest products, other fungi cause 

 stains, molds, and decays that are re- 

 sponsible for much deterioration and 

 loss in lumber, posts, poles, buildings, 

 containers, and in wood used for other 

 purposes. 



Not all of the fungi in the forests are 

 harmful : Many fungi contribute to the 

 health and growth of trees by convert- 

 ing the fallen leaves, twigs, and other 

 forest debris into humus, an important 

 constituent of forest soils and a source 

 of nutrient elements for tree growth. 

 Others combine intimately with the 

 tiny feeding roots on some trees to form 

 special absorbing bodies, called mycor- 

 rhizae, which are believed to enable the 

 trees to take up nutrients from the soil 

 more effectively than they would 

 otherwise be able to do. Through the 

 production of humus, fungi also tend 

 to create a soil reaction that is un- 

 favorable to the disease fungi that at- 

 tack the roots of seedlings and young 

 trees. A few fungi attack disease-pro- 

 ducing fungi directly. 



Diseases and fungi causing deteriora- 

 tion are commonly spread by wind, 

 water, insects, and bird life. Soil fungi 

 causing root rots and wilts may be car- 

 ried on the wheels of vehicles or the 

 feet of men or animals. The fungus 

 causing canker stain of the planetree 

 is carried on pruning tools and equip- 

 ment. Virus diseases, such as the 

 phloem necrosis of elm, are almost in- 

 variably spread by insects, as also are 

 some stain and decay fungi. 



THE EFFECTIVE CONTROL of forest 



diseases must be based on a sound 

 knowledge of them and of the forest 



Yearbook of Agriculture 1949 



environments under which they occur. 

 Both direct and indirect methods are 

 employed. Direct methods include the 

 use of sprays, dusts, and soil treatments, 

 the removal and destruction of affected 

 trees or parts, the prescribed use of 

 fire, and the removal of alternate hosts. 

 Sprays and soil treatments are used in 

 the nurseries to protect the seedling 

 trees against diseases, and sprays and 

 dusts to destroy the insect carriers of 

 diseases of shade trees, such as the 

 Dutch elm disease and the elm phloem 

 necrosis. Eradication is particularly im- 

 portant where a dangerous disease has 

 been accidentally introduced into a lo- 

 cality and is known to be of limited 

 distribution. This was the case when 

 the European larch canker was discov- 

 ered in a limited area in Massachusetts. 

 Thorough eradication was undertaken 

 immediately, and the disease appar- 

 ently has been eliminated. 



FIRE IN THE FOREST ordinarily does 

 more harm than good, but against the 

 brown spot disease of longleaf pine in 

 the Southern States it has a sanitary 

 effect when properly timed. 



The white pine blister rust offers an 

 example of a disease that can be con- 

 trolled through the removal of the al- 

 ternate hosts, currants and gooseber- 

 ries. The rust cannot spread directly 

 from pine to pine, but the spores from 

 the rust on pine are carried by the 

 wind and are able to infect currants 

 and gooseberries. Spores from the rust 

 developed on these are, in turn, capa- 

 ble of infecting white pines. The re- 

 moval of the currant and gooseberry 

 bushes to a safe distance from white 

 pines effectively protects the pines 

 from the rust. 



If a disease has become widespread 

 and well-established, eradication is 

 usually impracticable, and we may 

 have to learn to live with it and to re- 

 duce losses through indirect methods 

 of control. This applies to most of our 

 native diseases. 



The red rot of the ponderosa pine in 

 the Western States is an example. 

 The causal fungus enters the trunk 



