SOURCES OF APPLE BITTEE-EOT INFECTIONS. 21 



The transmission of the disease from susceptible varieties to rather 

 resistant varieties may also occur through the medium of spores 

 from infected fruits. Such destruction of the fruit of varieties nor- 

 malW resistant often occurs during years in which the weather 

 conditions particularly favor the disease, especially if the trees are 

 located in close proximity to susceptible varieties. 



RELATION TO CONTROL MEASURES. 



Under ordinary circumstances and in the average orchard, even in 

 sections in which bitter-rot is an especially serious disease, control 

 may be attained by means of spraying alone; but there are some 

 orchards in which the wintering-over or primary sources of infec- 

 tion are so abundant that frequent sprayings, even if most carefully 

 and thoroughly done, will not give adequate control. 



The writer (10) in 1914 carried on control experiments in two 

 orchards of this type in Arkansas and published his results in 1915. 

 Both of these orchards had sustained in previous years heavy losses — 

 from 20 to 50 per cent of the crop — ^in spite of frequent and thor- 

 ough sprayings with Bordeaux mixture. The removal of mummies, 

 cankers, and deadwood, supplemented by spraying, proved to be an 

 efficient control measure and was so reported. 



One of the orchards selected for the 1914 work was again used 

 for the experiments of 1915. This orchard, consisting of about 400 

 trees, was given its regular annual pruning in March, and the 

 pruners were instructed to pay special attention to the cutting out 

 of all cankers and deadwood. 



After the pruning was completed the orchard was again carefully 

 examined and all cankers and deadwood which could be found 

 removed. The pruners had done their work so well that few cankers 

 and little deadwood could be found, though, of course, it was realized 

 that to remove every canker and bit of deadwood was impossible. 



The trees were sprayed with Bordeaux mixture on June 15. The 

 disease became evident about July 15, and on July 19 small clumps 

 of rotted fruits could be seen on many of the trees. On the last- 

 named date the writer, with three helpers, picked off all the rotted 

 fruits that could be found, in order to prevent their serving as 

 sources of infection for the sound fruit remaining. The clumpsi of 

 rotted fruits also served as indicators as to the location of the orig- 

 inal sources of infection, which, when found, were removed. In this 

 way many cankers of various sizes which had been missed at prun- 

 ing time were removed. In fact, it may be said that this consti- 

 tuted practically a final cleariiig out of the sources of infection 

 which had lived over from the previous season. In the case of three 

 trees the percentage of infected fruit was so large that the entire 



