362 Report of the Mycologist op the 



THE EXTENT TO WHICH SPRAYING PREVENTED THE 

 DISEASE. 



The downy mildew first appeared on the unsprayed plants 

 August 7, and by August 21 it had injured the foliage to such an 

 extent that scarcely any cucumbers were produced after this 

 date. The damage was done almost wholly by the downy mil- 

 dew. The thirty-two rows of plants which had been sprayed 

 were in perfect health and vigor on August 21, and after this 

 date produced two hundred sixty dollars* worth of cucumhers which 

 represents approximately the benefit resulting from spraying. 



This benefit would, without doubt, have been considerably 

 larger if no unsprayed plants had been left. On the unsprayed 

 plants in Plats II and lY, the fungus was alU.wed to grow un- 

 checked and produce immense number of spores which the wind 

 scattered broadcast over the sprayed plants. These spores could 

 not attack the leaves from the upper side becaus'^ of the Bor- 

 deaux mixture. Probably they dropjied to the ground and were 

 carried to the undersurfaces of the leaves by the spattering of 

 rain drops. Here there was no Bordeaux mixture to hinder 

 them and so they readily gained access to the tissues of the leaf. 

 As a result, about August 21, the yellow disease-spots could be 

 occasionally found on the leaves of spraj^ed plants and from this 

 time on the disease gradually spread and shortened the crop con- 

 siderably. Had all the plants in the field been sprayed, the dis- 

 ease could not have obtained a start. The soil on which the 

 plants grew could not have been originally infested by the fungus 

 because no cucumbers had been grown on it for several years. 

 Hence, the only source from which the plants could receive 

 infection would be the spores coming from the neighboring fields, 

 the nearest of which was one-fourth mile away. Under these 

 conditions comparatively few spores would have fallen upon our 

 experimental field and it is very probable that we could have 

 kept the plants in perfect health until frost. 



*The actual amount was more than this, but exactly how much we do not know, and 

 desiring to be strictly within the limits of truth we will place it a little low and call 

 it two hundred sixty dollars. It is to be regretted that an exact record of the yield on 

 the different p'afs was not kept. The cucumbers were sold in the Wallabout Market, 

 Brooklyn, and because of the scarcity of cucumbers, they brought, on an average, 

 nearly four times the price which picklemen were paying for cucumbers raised on 

 contract. 



