Diseases of Economic Plants 



and middle states, and causes large loss. Affected fruits rot 

 into a soft, slimy, wet mass, this occurring often in transit. 

 On the leaves dark, watery spots, 3-5 mm. in diameter, ap- 

 pear. The spots later l^ecome dry and brown, and the 

 brittle tissue usually falls away, leaving a ragged, irregular 



hole. Spots on the 

 fruit are at first small, 

 2-3 mm., and watery, 

 and exude a gummy 

 liquid which later dries 

 to a white residue. 

 Infection proceeds to 

 the interior, and in a 

 few days the central 

 portion becomes a 

 rotten mass. Young 

 fruits are especially 

 susceptible. Care 

 should be taken in 

 picking to avoid 

 wounding the fruit, 

 and all affected fruits 

 should be most scrupu- 

 lously sorted out of 

 lots that are for ship- 

 ment. The season's 

 infection may originate 

 either from diseased 



Fig. 102. — Sclerotium rolfsii Sacc. grow- 

 ing upon a muskmelon at point of con- 

 tact with the soil. After Hume, 



seed or from soil. The use of seeds treated with mercuric 

 chlorid reduces infection. 



Mosaic. '-'^'^' -^^ — Two mosaic diseases of cucurbits are: 

 the White-pickle-mosaic, which affects many hosts, and the 

 Mottled-leaf-mosaic, common to only a few hosts. The 

 status of knowledge is much as in the case of other mosaics. 

 See p. 258. Inoculations are readily made by rubbing. In 

 the field, infection is carried by beetles and by the pickers. 

 Experiments have shown 18 species in 10 genera of cucurbits 



