APPLE DISEASES 



473 



thin black covering. The dead bark and 

 wood is penetrated by a whitish fungous 

 growth and has a strong mushroom odor. 

 Sometimes rhizomorphs are found on the 

 roots of an entirely healthy tree apparent- 

 ly causing no injury. 



The disastrous effect of the disease re- 

 sults from the girdling of the main roots 

 and the trunk, and from a destruction of 

 the activity of the sap-wood. This brings 

 about root starvation, a checking of the 

 ascent of water through the wood and, as 

 a consequence, the eventual death of the 

 whole tree. 



Cause 



The cause of this disease is one of the 

 higher fungi known as Armillaria mellea 

 (or varieties) and commonly called, from 

 its usual light, yellowish-brown color, the 

 honey mushroom. Several forms or vari- 

 eties of this fungus have been found on 

 the Pacific coast attacking fruit trees or 

 growing from the decaying stumps and 

 roots of oaks and other native forest trees. 

 The following general description of the 

 typical Ar»iilla)-ia mellea. however, will 

 serve sufficiently well to identify the 

 mushroom causing the disease under con- 

 sideration. 



Fruiting bodies or toadstools occurring 

 in tufts or clusters, honey-colored or light 

 brown; irregular ring (annulus) on stem 

 near the top; cap slightly elevated at 

 center; margin inrolled; later flat or con- 

 cave with margin upturned. Cap varying 

 from nearly white to reddish-brown, 

 darker toward center. Caps vary in size 

 and stems in length. Gills under cap radi- 

 ating from center shed innumerable 

 spores which are blown about or other- 

 wise disseminated. 



Life History and .lletliod of Siiread 



It is believed by many that the fungus 

 gains its entrance, more often, if not ex- 

 clusively at points where the root or the 

 crown of the tree has been injured by 

 cultivation, by the attacks of borers, or 

 by the presence of a crown gall, etc. When 

 once it has entered the tree, it sends out 

 delicate filaments both into the bark, 

 where, given the right conditions, it 

 spreads rapidly, and also, by way of the 



medullary rays (silver grain), into the 

 wood, where it spreads more slowly. 



The disease spreads fast from the point 

 of attack up and down the root or trunk, 

 apparently working most rapidly in the 

 cambium region. Little effect on the tree 

 is at first noticeable until the decay com- 

 mences to girdle the trunk, after which 

 the progress of the disease is rapid and 

 the death of the tree only a question of 

 one or two seasons. 



When the decay has progressed suffi- 

 ciently and the fungus is thereby richly 

 supplied with reserve nutriment, the 

 fruiting bodies or mushrooms may be 

 formed. In their young condition these 

 are edible. Abundant moisture is neces- 

 sary for their development, consequently 

 they are not met with, as a rule, till the 

 fall rains have begun. The clusters of 

 mushrooms usually appear at the point 

 where the trunk enters the earth and may 

 encircle its base. Often they rise through 

 the soil from a diseased root or they may 

 be attached to rhizomorphic strands con- 

 nected with crown or roots. 



Control Measures 



The suggestions presented in the fol- 

 lowing paragraphs regarding possible 

 modes of treatment for this disease are 

 in no way to be considered as definite 

 recommendations. The reason for this 

 appears when it is said that nowhere, to 

 the writer's knowledge, have thorough or 

 long-continued investigations of possible 

 orchard control methods been carried out 

 to a successful conclusion. Furthermore, 

 information as to the way in which the 

 trouble may enter an orchard and the 

 exact manner of its spread, is incomplete 

 and unsatisfactory. Consequently, the 

 writer is not warranted in stating that 

 any of the methods described here are 

 sure to give satisfactory results. It is to 

 be hoped, however, that intelligent grow- 

 ers will try out various methods of treat- 

 ment experimentally. 



The prevalent, but not yet convincingly 

 substantiated, idea that buried roots of 

 forest trees in newly cleared land are a 

 dangerous source of infection for young 

 orchard trees, has led to the suggestion 



