EXPERIMENT STATION BULLETINS. 393 



PBEVENTIVE MEASURES. 



The manner in which these fungi gain an entrance into the trunVcs and limbs 

 of trees, namely through wounds, suggests the importance of treating all exten- 

 sive ruptures of the baric with some protective coating. This is especially needful 

 in the removal of large limbs. In such cases the natural process of healing 

 over is often not accomplished for a number of years and during the process 

 some wound fungi are pretty certain to gain a foothold unless measures are taken 

 to exclude the spores. This is most frequently accomplished by painting or coat- 

 ing the cut surface with some good paint, hot tar or liquid wax. The cut should 

 be made close to the main branch or trunk in pruning thus favoring quicker 

 healing and avoiding stubs which die at the end and invite the attacks of these 

 wood-destroying fungi. Lower branches which are shaded too much, as in 

 crowded and unpruned orchards, are constantly dying back for want of nourish- 

 ment. In such cases the dead portions fall a prey to wound fungi which may 

 in time reach the main branches and trunk. Such dying limbs should be removed 

 and the wounds covered. "Where decay has begun in the trunk it is often difla- 

 cult to prevent its progress. If confined to a limited portion of one side the 

 decaying wood may be cut out as far as possible, the surface treated with a strong 

 solution of copper sulphate and coated with tar, to be renewed as often as neces- 

 sary. Removal and burning of the fungous outgrowths will also prevent the 

 formation of spores. 



INJURIES OP FRUIT TREES NOT DUE TO THE ATTACKS OP PARASITES. 



Among the so called mechanical injuries of fruit trees and other plants are 

 some of quite common occurrence. In most cases they are due to sudden changes 

 or unusual degrees of temperature and affect mostly such plants as are not quite 

 hardy. 



"Sun Scald" is a term usually applied to injuries of the trunk and larger 

 branches of trees arising from the killing of the inner bark and cambium by the 

 action of the sun's rays. The south and west sides of trunks are usually affected 

 and young trees are more subject to injury than old ones. The injury often 

 occurs late in winter and early spring, especially when clear v/arm days are 

 followed by severe cold at night and especially if growth has been prematurely 

 started. The same trouble may arise also in summer on exposed trunks and limbs. 

 The injury is characterized by the splitting and loosening of the bark which often 

 becomes entirely detached. Sun scald offers a favorite place of entrance for 

 wound fungi which sometimes cause the death of the tree. (See Pig. 41.) 



"Prost Cracks" arise from the combined action of sun and severe freezing 

 leading to longitudinal ruptures or cracks in the bark and wood. They usually 

 occur, as does sun scald, in trees which have made a late autumn growth and 

 which enter the winter with the tissues full of water and improperly matured. 

 Peaches, plums and ■cherries, especially the sweet varieties of the latter, are more 

 subject to these injuries than are apples and pears. 



Prevention of these two injuries can be secured only by protecting the trunks 

 from the direct rays of the sun by means of burlap, straw or other wrapping or 

 shading devices, and by inducing the trees, so far as possible, to thoroughly 

 mature their wood before winter sets in. The latter aim may usually be realized 

 by the use of the proper fertilizing elements, as potash, in the soil, and especially 

 by the use of cover crops sown late in summer, to utilize any excessive moisture 

 which the soil may contain at this time and thus induce earlier maturity of the 

 trees. 



"Sun Scorch" of foliage is, as its name implies, due to excessive heat of the 

 sun on foliage of plants deprived of a sufficient water supply as during a drouth. 

 The occurrence of hot, dry winds, especially on tender foliage, also produces a 

 similar effect. This trouble has been noted on foliage of cherry and maple trees, 

 especially where situated on shallow soils with underlying rock. While hardly 

 under the control of the grower the proper location of orchards accompanied with 

 constant stirring of the surface soil to retain moisture should be considered as 

 partial preventive means. 



"Two unusual troubles of apple foliage" have been noted in New York, the 

 first being "frost blister" and the latter the spotting of foliage caused by spraying. 



50 



