158 



FUXGl AXD FUXGICIDES 



The disease appears in the field as a blackish growth on 

 the outer bud scales. It is not noticeable at first, and 

 when closely examined will be seen to consist of a cen- 

 tral dot or ring, surrounded by larger rings. During 

 damp weather the black growth develops rapidly, some- 

 times in the form of circles, and sometimes simply 

 spreading without circles, as in Fig. 60 a. AYhen the dis- 



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II' 



\ ' 



a 



FIG. 69. 

 a, Spot (liseafe of onions; b, spores. 



ease first appears it only affects the outer scales, but 

 later it penetrates deeper and causes rot. 



When highly magnified tlie black specks on the 

 bulb scales resemble Fig. 69 b. Each consists of a mass 

 of mycelium having long, black, pointed bristles, around 

 the bases of which the small, slightly curved spores are 

 produced in great numbers. These spores are easily 

 blown upon surrounding bulbs, where they may germi- 

 nate and start the disease again. 



Treatment. — One of the best safeguards against 

 this disease is to put dry onions in dry bins, in cool and 

 dry storerooms. The onions should not be allowed to 



