The Bulletin. 13 



the more superficial development of the rot on the lower stem, and the 

 absence of internal wood discoloration distinguish the latter. 



Cause. — This disease is caused by the fungus Fusarium tracheiphi- 

 lum. It is closely similar in form and habits to the fungi causing wilts 

 of cotton, watermelon, tomato, Irish potato, sweet potato, etc. But the 

 cowpea fungus seems not to be able to infect these plants, and the 

 cowpea not to be susceptible to the other wilt fungi. However, two or 

 more of these wilt fungi may sometimes inhabit the same soil. The 

 fungus lives in the soil from year to year and increases with the suc- 

 cessive planting of susceptible varieties of cowpeas on the land. It 

 enters the plants through the roots, grows upward in the sap-tubes of 





Fig. 5 Wilt of cowpea. The plant on the left shows no evidence of the disease. The other two 

 show advanced stages. 



the stems discoloring the wood tissues along its path. The interference 

 with water conduction brings on the symptoms of wilt. After a plant 

 is dead the fungus may grow out to the surface and form a crop of 

 pinkish spores there. 



Dissemination. — The chances for the spores to play an important 

 part in the spread of the disease seem relatively slight ; and seed prob- 

 ably do not act as carriers, through external contamination, with great 

 frequency. The feeding of infected plants to stock will introduce the 

 disease into the manure, where it flourishes ; and by this means it may 

 be scattered over the farm. The fungus remains alive, although dor- 

 mant, for long periods in thoroughly dried stalks of affected plants, 

 and well cured hay may produce manure contamination. Transfer of 

 infected soil in any way will spread the disease. In using soil for 

 legume inoculation be sure that this and every other soil disease is 

 absent from the field from which it is taken. 



Infection. — Infection seems to occur entirely through the roots. Ne- 

 matode injury furnishes a ready way of entrance for the fungus, and 

 the disease is always worst where nematodes infest the soil along with 

 the wilt fungus. But either trouble may exist ' independently of the 



