964 



MICROBIAL DISEASES OF PLANTS 



crop suffering rather than the tree. The leaves sometimes exhibit a 

 blackening or browning of the petioles and veins, while the intermediate 

 tissue may develop brownish, circular or angular spots. The disease 

 does not cause serious defoliation of the tree. The catkins are probably 

 not affected. It is upon the young nuts that bacteriosis is especially 



I 



Ji 



FIG. 197. Walnuts affected by Bacteriosis, mostly stigma or blossom-end infection. 



(After C. 0. Smith, Calif. Bull. 231.) 



destructive, and it would be of little economic importance did it not 

 attack these. Many of the nuts may become infected and fall when 

 they are /^ to J^ inch in diameter and continue to drop throughout the 

 summer. A conservative estimate of the loss places it at 50 per cent 

 in badly diseased groves. The most common point of infection is at 

 the blossom end, although, it may start at any place on the nut. In 



