April, '10] NORTON: TEACH DISEASES 233 



Spray and Other Chemical Injuries 



There are still some unsolved problems connected with injni'ies 

 from copper, arsenic and other spray materials, the peach being 

 especially sensitive to such, though much has been cleared up by 

 Bain and others. Some peculiar physiological disturbances come from 

 the use of oils, and much injury resulted especially in the old days 

 of kerosene and crude petroleum spraying for scale. I do not know 

 of any one having yet worked out the physiological effect of oil upon 

 trees or upon fungi. Whether the peculiar rough bark often seen 

 on peaches sprayed with oil is due to the latter or to recovery from 

 scale I cannot say. 



Some of our mysterious troubles may be due to dipping in oils or 

 other materials. Close (Delaware) found severe injury to peach 

 dipped in crude petroleum and more when dipped in kerosene. 

 Symons (Maryland) found injury from oil dipping in some cases. He 

 found more injury when roots were dipped. 



Silver Leaf 



A condition of peach foliage called silver leaf due to unknown 

 causes has been known in England for years and is reported as serious 

 and contagious. A silvery appearance is common on peach leaves in 

 autumn in this country. I was told by Professor A. L. Quaintance 

 in 1901 that this was due to the work of a mite, but I can find no 

 publication on this trouble except the description of the silvering 

 mite by Banks in 1905. 



Split Pit 



Split pit is a common and not definitely explained condition. In 

 England it is attributed to excessive and unequal growth of inner and 

 outer parts of the fruit dvie to rapid growth at fruiting time. Piper 

 says that in the western United States twig borers are the cause of 

 some of it. Another writer says these only enter the previously split 

 pits. It was noted as serious in California in 1904. 



I shall now mention some conditions due to various causes, which 

 we may best group under their most noticeable symptoms. 



Root Rot 



Frequently trees blossom out then stop growing or make an un- 

 satisfactory growth and then die. In such cases the root is often full 

 of fungous mycelium. Several fungi (for example, Clitocybe 

 parasitica), (Missouri and Oklahoma) and other Basidiomycetes 



