6o2 MICROBIAL DISEASES OF PLANTS 



Control. — On small areas, heavy mulching of straw along either 

 side of the row is suggested as a possible means of preventing the 

 distribution of the disease. 



Tomato Blight 



Bacterium (?) michiganense — Erw. Smith* 



The disease is distinct from the wilt, caused by B. solanacearum,m 

 that there is not the sudden collapse of the whole plant, but rather a 

 slow yellowing or wilting of the leaves, one at a time. The causal 

 organism produces cavities in the pith and bark as ,well as- in the 

 vascular system. 



Walnut Blight or Bacteriosis 



Psetidomonas juglandis — Pierce 



History and Distribution. — -Attention was first called to this dis- 

 ease as it occurred in California by Pierce f in 1893 although it had 

 been observed in Los Angeles Counl^y in about 1891. Outside of 

 California, it is known to occur in Oregon, Texas and midway down' 

 the Pacific coast- of Mexico. What appears to be a similar trouble 

 has been reported from New Zealarid and France. 



' Symptoms. $ — AU of the new, tender, growing parts of the tree, 

 such as young nuts and branches, petioles of leaves, midveins, fine 

 lateral veins and adjoining parenchyma are suljject to the attacks. 

 On the branches, the disease always starts in the young succulent 

 grbwth and manifests its presence by small, discolored areas which 

 under favorable conditions may extend 2 to 3 inches along the green 

 shoot. As the infection progresses, the central portion of the lesion 

 turns black and is surrounded by a water-soaked margin. In the, 

 later stages, the whole diseased area becomes blackened and in many 

 instances has a somewhat shrunken, dried-out, deformed, cracked 

 appearance due to the drying out of the tissue. In severe cases the 

 tissue is killed inwardly to the pith, while in the milder attacks only 

 the"bark and wood are diseased. As the wood hardens, the infection 

 is checked, and the vitality of the tree is not affected to any extent, the 



• Smith, Erw., Science, N. S., Vol. XXXI, 803. p. 794. 1910. 



4 Pierce, N. B., B,ott Gaz.,3i; 272-273, ISOI.. ' 



t Smith, C. O., "Walnut BHght," Bull. 231, Calif. Exp. Sta., 320, 1912. 



