THE MONTHLY BULLETIN. ' 275 



made in the Insecticide Laborator^^ of the University of California. The 

 inforniation has been collected from so many sources that individual 

 ackiiowledii'ments would involve the incorporation of an unwieldy bibli- 

 ogrupliy and could not well be made complete. 



Grateful acknowledg-ment is therefore made to all of the government 

 and state experiment station workers who have contributed a share in 

 investigating these problems, to the county horticultural commissioners, 

 and to my associates who have made valuable suggestions in the 

 classifications. 



CONCLUSION. 



It must be admitted with chagrin that our chemical knowledge of 

 insecticides and fungicides is j^et too imperfect to predict with absolute 

 confidence the results to be obtained from the use of a new material or 

 an untried combination of materials. The final decision must be made 

 as the result of carefully planned practical field experiments. 



The table of compatibilities is therefore presented with considerable 

 hesitation for the first time and is offered for your criticism, in order 

 that if any of the classifications are incorrect, or do not correspond with 

 your experiences, the matter may be discussed and the faults corrected. 



THE OAK FUNGUS DISEASE OF FRUIT TREES. 



Address, California State Fruit Growers' Convention, Davis, Cal., June 1-6, 1914, by 

 Prof. "W. T. HoRNE, University of California. 



The oak fungus disease or fungous root rot caused by the fungus 

 Armillaria mellea, is a very common and a very serious disease of 

 orchard trees in California. Its most striking characteristics are its 

 mark(Hi localization and slow progress. The fungus which causes it 

 probably existed in the roots of wild trees, attacking living roots, but 

 working so slowly that vigorous trees were not killed, and also persisting 

 in the dead wood, causing roots to decay. It appears that many wild 

 trees are infected in nature, and I do not have sufficient evidence to say 

 that oaks are more subject to infection naturally than other trees. Not 

 all roots in the soil are infected, so that we can not say that because an 

 oak tree grew in a given place oak fungus will appear there. 



When the roots of a fruit tree come sufficiently near to infected wood 

 in the soil the fungus grows over and attacks the living roots. We must 

 Iselieve that this may happen long after the original clearing, because the 

 fungus will not die out of the soil until the root in which it lives is very 

 completely decayed. It is probable that new infections have appeared 

 ten years after planting an orchard. 



The course of the disease is now well understood by fruit growers. 

 Often several trees have died before particular attention was given to 

 the trouble. It was then found that two or three trees nearest those 

 which have died were dying or diseased. The trouble can be recognized 

 with Certainty only by an examination of the roots. Usually two or three 

 years will elapse after the first signs of weakening have appeared before 

 the tree dies, and after the first collapse some part of the tree may start 

 up and continue to grow for an indefinite time, finally to be blown over 

 by the wind or to die completely if it does not first exhaust the grower's 



