278 MONTHLY BULLETIN. 



THE IMPORTANCE AND PREVENTION OF WOOD 

 DECAY IN FRUIT TREES. 



By W. T. HoRNE, 

 Associate Professor of Plant Pathology, University of California, Berkeley. 



In large forest trees the decay and disappearance of wood in the 

 center give us the well-known hollow trees. Such trees may live for 

 many years but are liable to be broken down or blown over. In our 

 orchards also wood decay is common. Decayed orchard trees may live 

 for some years and bear reasonable crops, but usually a heavy load of 

 fruit breaks off one limb after another and the tree becomes a worthless 

 stub. Peaches are especially subject to rapid loss in this way, but the 

 present discussion applies to all our fruit trees. The decays considered 

 in this paper are those which start from some surface of dead bark or 

 wood and spread through the center of trunk and limbs without affect- 

 ing, at least for some time, the bark and cambium. 



This kind of decay should not be confused with the oak fungus dis- 

 ease which affects primarily the roots but may spread up some little 

 distance into the trunk. It affects perfectly sound and healthy roots 

 and kills the bark, causing it to decay in a characteristic manner, and 

 then spreads into the wood causing a soft, light-colored decay. In 

 contrast with the oak fungus disease, the common wood decays do not 

 attack perfectly sound healthy trees with unbroken bark, but the rot 

 starts from some exposed wood and then works up and down through 

 the center of the tree. 



IMPORTANCE OF WOOD DECAYS. 



Fruit trees with decayed centers may bear heavily but usually such 

 trees rapidly become cripples. Not only is the carrying strength reduced 

 but there is good evidence that many of the dead limbs seen in orchards 

 are due to wood decay which has worked outward to the bark. Mr. 

 C. J. Rodgers, of Watsonville, working in our laboratory, has shown that 

 the so-called sappy bark disease of apples is due to one of these fungi. 

 That such decays are conunon is generally conceded, but no definite 

 data have been available. Accordingly jMr. W. W. Thomas made care- 

 ful counts in representative orchards in three regions — coast valley, 

 interior valley, and foothills. "While the results secured may not be 

 at all final, they clearly show several facts with respect to stone fruits. 

 First, contrary to anticipation, wood decays are more prevalent in the 

 hot interior valleys and foothills than in the cooler and more humid 

 coast valleys. The winter moisture in the three regions is not very 

 different, while the more frequent sunburn and wider cracking of large 

 pruning wounds doubtless account for the facts found. Also in the 

 orchards examined there had been less grafting over of bearing trees in 

 the coast region. Second, it appears that more than half the stone 

 fruit trees of bearing size in California are certainly affected with 

 wood decay. Third, not much more than 2 per cent of stone fruit 

 trees are free from sunburn or large Avounds. Fourth, by far the 

 largest part of infection comes from sunburn, large pruning wounds, 

 or grafting over stubs. Fifth, fully two-thirds of the decay is caused 

 by the common oyster shell fungus, Polystictis versicolor. A dozen 



