130 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



through a dormant period in a similar manner to the behaviour 

 of the resting-stage of the cushion of apple scab. It is 

 probably in these cushions that the fungus over-winters. When 

 the conditions are favourable the mass of hyphae grows and 

 forces up and finally ruptures the bark. At first the pustule 

 has a shiny black appearance, but when the cushion has burst 

 through the bark it becomes covered with spores and short 

 conidiophores, and appears dusty and dark olive-brown. 



These spores act again as a source of infection, and, judging 

 by the similarity of the form on the willow twig to the dormant 

 stage of apple scab on such apples as Cox's " Orange Pippin," 

 this is the origin of the early infection on the leaves of the willow. 



In dealing with other bark troubles of willow, such as 

 Physalospora gregaria (Sacc), often called willow canker, which 

 is common in Somerset on basket willows {S. triandra, 

 S. viminalis, etc.), it has been found that the disease is 

 very much increased by the habit of cutting the rod of the 

 required length only. In other districts where the custom has 

 been to cut right out down to the stool and trim the rod 

 afterwards, the disease has been much less. In dealing with 

 osier willows, or stools of willows kept for commercial or 

 useful purposes in nurseries, the rod should be cut as low 

 down and as near to the stool as possible. Any long stub 

 left forms a home for the pustule form of this scab, as well 

 as for the cankers of the Physalospora. Long stubs should 

 therefore be avoided. 



All diseased twigs should be cut out so far as possible during 

 the winter, and burnt before the dormant pustules awaken and 

 form spores. If the value of the willow or the usefulness of 

 the withies will warrant the expenditure of money and labour, 

 a winter wash of copper sulphate — 4 lbs. of copper sulphate, 

 100 gallons water — could be given in the winter, or lime sulphur 

 — I gallon to 29 gallons water — might be tried in the spring. 

 In the case of osiers, spraying the stumps with Bordeaux 

 mixture after cutting might be tried. Bordeaux mixture could 

 also be used in the apple scab strength, i.e. 4.4.50, just after 

 the leaves unfold. 



As very few data are available as to spraying on trees, 

 other than fruit trees, a nurseryman would probably employ 

 the spray that he was using on his fruit trees and already had 

 in his possession. 



