182 Diseases of Economic Plants 



be practiced and infested soil should not be replanted to 

 melons until the wilt fungus is largely diminished in quantity. 

 This will probably take more than four years, 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 manure. 



The practice of raising cowpeas after melons leads to the 

 presence of some melon vines in the cowpea hay, and this 

 likewise leads to the presence of the causal fungus in the 

 compost heap. Manure so exposed to infestation should never 

 be placed on land which is still free from the germ, or which 

 is to be used for melon culture, since this is certain to spread 

 the wilt. 



There is no objection to the use of stable manure which 

 does not contain the fungus, but experience has shown 

 that when the wilt once gains entrance to the compost heap 

 or barnyard, it remains there for years, and all of the manure 

 taken out of such a yard is likely to spread the disease. Hence 

 it is exceedingly dangerous, in regions where the wilt pre- 

 vails, to use any stable manure on the field where melons are 

 to be planted. 



Varieties resistant to this disease have been developed by 

 the United States Department of Agriculture by crossing the 

 citron, which possesses high resistance, with the watermelon, 

 and then by practicing selection to attain the desired 

 edibility. 



Wilt^^o- '^^o (Bacillus tmcheijMlus EFS.). — The cucum- 

 ber, muskmelon, pumpkin and squash are susceptible but 

 not the watermelon. 



The disease has been reported from many states — among 

 them Nebraska, Wisconsin, Maryland, Massachusetts, 

 Indiana — ■ and is presumably present in many others. 



The attack in first stages causes the vine to droop through- 

 out its length. This is followed l)}-- death. The infection is 

 spread by insects, particularly beetles on which the bacteria 

 probably hibernate to some extent. 



