TOMATO DISEASES 



1979 



those produced hy the stem rot of cucum- 

 bers. Tomatoes, however, are not as sus- 

 ceptible to timber rot as cucumbers, al- 

 though when affected the crop is great- 

 ly injured. We have repeatedly grown 

 crops of tomatoes in soil badly infected 

 with the timber rot fungus but as a rule 

 only a few plants become diseased, and 

 from this it would appear that tomatoes 

 are generally immune to attacks from 

 Sclerotinia. 



Sclerotinia is a sterile soil fungus, and 

 gains entrance to the plant near the sur- 

 face of the soil. When the plant becomes 

 infected the fungus traverses the stem 

 and breaks out some distance above the 

 ground, the part of the stem affected be- 

 coming whitish in appearance. Small, 

 hard, black masses called sclerotia, about 

 one-thirty-second or more of an inch in 

 diameter, make their appearance on the 

 surface of the stem. These sclerotia are 

 capable of throwing out filaments, or ger- 

 minating and affecting other plants. Dry- 

 ing the soil greatly increases the activity, 

 and infection of succeeding crops is there- 

 by materially increased. 



Control 



Since the disease has not proved to be 

 of great importance on tomatoes in North- 

 ern greenhouses, remedial measures are 

 not urgently needed; but should it ever 

 become so, soil sterilization will be found 

 efficacious, and the treatment of the soil 

 with formalin may prove valuable. 



G. E. Stone, 

 Massachusetts Bulletin 138. 



Western Tomato Blight 



P. D. Bailey 



This disease of tomatoes has, for some 

 time, caused severe losses to growers and 

 in certain sections has forced them to give 

 up what would otherwise be a very profit- 

 able crop. It is apparently confined in 

 distribution to the region of the North- 

 west known locally as the "Inland Em- 

 pire." In Oregon it is serious only in 

 the eastern sections of the state and west- 

 ward along the Columbia river. 



This disease is characterized by a grad- 

 ual yellowing and curling of the foliage; 

 as the leaf tissue turns yellow the veins 



take on a purplish color. The plants are 

 dwarfed and fail to mature fruit. The 

 stem of an affected plant is thickly cov- 

 ered with glandular hairs, the stain which 

 they produce seeming to be much more 

 abundant than from a healthy plant. The 

 root systems of diseased plants are of- 

 ten very different from the normal healthy 

 ones. The smaller lateral roots show the 

 effect of some organism. They are at first 

 discolored and finally die back. Where 

 such a root is killed, several more start at 

 its base from the main root to replace it 

 These are often killed and the same 

 thing happens again, so that a cluster or 

 mat of short laterals is produced instead 

 of the long normal feeding roots. This 

 condition has led to an investigation for 

 the presence of a fungus which attacks 

 the roots from the soil. 



Investigations have been carried on for 

 some time at the Washington State Ex- 

 periment Station, where Professor H. B. 

 Humphrey has succeeded in proving that 

 the causal fungus is a species of a com- 

 mon soil organism. This fungus is a dif- 

 ficult one to combat. There are several 

 further experiments to be tried toward 

 this end. So far the following courses 

 are recommended: 



Treatment 



The work at the Pullman station seems 

 to show that the most help along control 

 lines at present can be obtained if the 

 seed bed is done away with. The seed 

 should be planted four to a hill and in 

 hills three or four feet apart in the field. 

 Individual forcing boxes should be used, 

 if practical, until the plants are five or 

 six inches hign. After removing these, 

 thin the plants so as to have one to a 

 hill. 



The experiments where this method 

 was tried showed a very small percent- 

 age of blight as against varying losses 

 where checks were kept by setting plants 

 from seed beds. The difference probably 

 is due to the fact that the roots are in- 

 jured in transplanting, thus furnishing 

 the fungus an opportunity to enter. 



Besistant Strain 



Another course which may well be pur- 



