280 MONTHLY BULLETIN. 



other fungi will probably include nearly all of the common wood decay 

 forms in orchards. 



We believe wood decay is a trouble of stupendous importance to the 

 California fruit industry. Professor Wickson says: "There are 

 instances in the earliest-settled parts of the state, where peach trees 

 above fifty years old are still vigorous and productive. * * * Some 

 trees have, in fact, gone along in thrift * * * because they have 

 never been allowed to sunburn, * * * have never been pruned with 

 an axe, and have never lost a limb nor had a wound into which decay 

 could penetrate and descend to the root." 



CAUSE OF WOOD DECAY. 



Wood decay does not set in because a tree is old or because it is 

 weakened by lack of food or water. Neither is it a natural process 

 necessarily following exposure to air and moisture. Serious wood decay 

 is due to infection by any one of several fungi which gain entrance at 

 some point where the wood is exposed or where the bark is dead. The 

 fungus grows in the wood, digests it and uses it up, finally leaving only 

 a little ash. This process of digestion constitutes decay. Infection 

 must take place from spores which fall on dead bark or into cracks of 

 wounds. These spores are formed on definite bodies, of which the 

 brackets or oystershell-like structures are examples. The spore-bearing 

 brackets grow almost entirely during winter, so spores will not be 

 scattered during the dry summer. The spores must lodge in a moist 

 crevice in order to grow and establish the fungus in the wood. 



TREATMENTS. 



Prevention of ordinary wood decay depends wholly on protecting 

 exposed wood from infection by spores of these fungi. Abundant 

 moisture is doubtless also necessary. 



Measures will vary according to the kind of trees to be dealt with. 



First, for small trees just planted the greatest importance attaches 

 to shaping the tree so that later there will be no need to remove large 

 limbs — in other words, get a simple framework. The tree should also 

 be shaped for strength — so that neither the load of fruit nor orchard 

 operations will be likely to break off large limbs. Wounds should be 

 treated as recommended below, but it appears that wounds which heal 

 over in one year rarely become infected. 



Second, trees of some size which have wounds and are liable to infec- 

 tion but are still apparently sound. According to our studies this will 

 include a little less than half our bearing stone fruit trees. All horti- 

 cultural procedure which I have seen recommended is inadequate for 

 protecting these trees and I take the liberty of suggesting a method on 

 the basis of our present information. 



A. When a cut or wound is made exposing the wood of a tree it 

 should be wet with a germicide. This should be done immediately or 

 as soon as the surface has dried and before cracks have formed. 



B. Irmnediately after disinfection, as soon as dry enough, the wood 

 should be covered with some sealing paint to prevent cracking as far 

 as possible. 



C. This process must be repeated for all wounds every year until 

 they are healed over. The reason for this is that no sealing material 

 can be trusted to last more than one season. 



