TOMATO DISEASES 145 



vessels are found to be filled with fungous threads, 

 which shut off the water supply. 



The infection in the Fusarium wilt appears to come 

 entirely from the soil. Little is known of its manner 

 of spread, except that the cultivation of a tomato crop 

 in certain districts appears to leave the soil infected 

 so that a crop planted the next year will be injured or 

 destroyed. The fungus does not remain in the soil 

 for a very long time in sufficient abundance to cause 

 serious harm. A rotation of crops that will bring 

 tomatoes on the land once in three years has been 

 found in Florida to prevent loss from Fusarium wilt. 



This fungus does not attack any other crop than 

 tomatoes, so far as known, though it is very closely re- 

 lated to species of Fusarium producing similar dis- 

 eases in cotton, melon, cowpea, flax, etc. Fusarium 

 wilt has not been found in fields and gardens in the 

 northern states, but tomatoes in greenhouses there are 

 sometimes attacked by it or a related Fusarium, which 

 also occurs in England. When greenhouse beds are 

 infected the soil for the next crop should be thoroughly 

 sterilized by steam under pressure. 



Sclerotium wilt. This disease resembles the two 

 preceding in its effect on the plant, which wilts at the 

 tip first, and gradually dies. Its geographical range 

 is more restricted. It seems to be confined to north- 

 ern Florida and the southern part of Georgia and Ala- 

 bama, where it occurs in gardens and old cultivated 

 fields. The fungus causing this wilt attacks the root 

 and the stem near the ground, working in from the out- 

 side. There is not the browning of the wood vessels 

 characteristic of the two preceding diseases. If an 



