272 Diseases of Truck Crops 



WILT, YELLOWS 

 Caused by Fusarium tracheiphila Ew. Sm. 



In the light sandy to loamy soils, wilt is the greatest 

 drawback to pea culture. The disease is most pre- 

 valent in the Southern States. 



Symptoms. It does not seem to attack young 

 seedlings, but appears only when the plant is about 

 six weeks old and upwards. In the field, scattered 

 plants turn yellow and begin to drop their leaves, the 

 stems become bare (fig. 50 a), and the plants finally 

 die. On pulling out a diseased plant, the main root 

 will apparently be sound, but the lateral rootlets 

 will be dead, marking the seat of infection. A 

 more definite symptom of wilt is a browning of 

 the interior fibrovascular bundles of roots, stems, 

 and petioles. This may be readily ascertained by 

 splitting open lengthwise a root or stem of a sus- 

 pected plant. 



The Organism. From unpublished work by the 

 author, it is definitely proven that F. tracheiphila is 

 distinct from Fusarium wilts of the cotton, okra, 

 and watermelon. The Fusarium wilt of the cowpea 

 is caused by F. tracheiphila, which produces only the 

 conidial stage and has no relationship whatsoever 

 with Necosmospora, or any other ascospore stage. 

 The cowpea Fusarium may be found in fields which 

 are also infected with okra Fusarium. In this case, 

 the field is infected with two distinct organisms, thus 

 making it sick to both cowpeas and okra. The cow- 



