316 DISEASES OF ECONOMIC PLANTS 



The wilt is readily recognized from the fact that the 

 leaves first droop, as though they were suffering from want 

 of moisture, rapidly wilt, and soon die, the runner dying 

 with the leaves. Soon the whole plant is dead. Upon 

 cutting the main tap root across near the surface of the 

 ground, such plants are found to present a yellow color 

 in the wood, making a distinct contrast with the white 

 color of the healthy plants. This one character, taken 

 together with the wilted appearance of the vine, enables 

 recognition of the true watermelon wilt. The further 

 fact that a field once infected shows the same disease in 

 succeeding years in the same or in extended areas is an 

 additional recognition mark. 



Its spread may occur in the ways mentioned under soil 

 diseases and in particular through the use of infected 

 manure. 



To restrict it to its present confines crop rotation should 

 ])e practiced and infected soil should not be replanted to 

 watermelons until the wilt fungus is largely diminished in 

 quantity. This will probably take more than four j^ears, 

 possibly eight or ten years, and even at the end of that time 

 it is best to try a few hills before planting the whole field 

 to melons. Cattle should not be allowed to pasture upon 

 diseased vines and thus spread the wilt through the manure. 



The practice of raising cowpeas after watermelons leads 

 to the presence of some watermelon vines in the cowpea 

 hay, and this likewise leads to the presence of the causal 

 fungus in the compost heap. Manure so exposed to infec- 

 tion should never be placed on land which is still free from 

 the germ, or which is to be used to raise watermelons, 

 since this is a sure way of spreading the wilt. 



