TWO EPIDEMICS OE POTATO BLIGHT AND ROT. 183 



SUMMARY. 



Adverse weather conditions were responsible for severe epi- 

 demics of late blight and rot of the potato in Maine, particu- 

 larly in Aroostook county, during the seasons of 1907 and 

 1909. (P. 165.) 



Blight is caused by a parasitic fungus which spreads through 

 the leaves, killing the tissues as it goes. Each blighting leaf 

 produces thousands of minute fungus spores each capable of 

 infecting another leaf, or a potato tuber. (P. 166.) 



Bordeaux mixture forms a protective film on the healthy 

 leaves, kills the spores which fall thereon, and also kills those 

 produced on the diseased leaves at the time of application. 

 (P. 166.) 



]\Iuch, if not all, of the disease comes originally from plant- 

 ing diseased seed tubers. Rain, dew, wind, insects, etc., are the 

 chief agencies in disseminating the spores. (F. 173.) 



Late blight is most destructive in rainy or cloudy weather. 

 Hot, dry, sunshiny weather is fatal to the blight spores, and 

 outbreaks of the disease never occur under these conditions. 



(P. 173O 



Much of the bordeaux mixture used is carelessly and 

 improperly prepared. Only standard bordeaux mixture con- 

 taining 5 pounds of copper sulphate and 5 pounds of lime to 50 

 gallons of water should be used. The most adhesive mixture 

 is made by diluting the copper sulphate and lime solutions each 

 with half of the water and then quickly and thoroughly mixing. 

 The ingredients should he iveighed and measured and the pro- 

 portions should not be varied. (P. 174.) 



The sprayers carry too few nozzles per row and do not have 

 sufficient adjustments of nozzles. Pumps should be powerful 

 and nozzles in such condition that the spray will be delivered 

 forcibly and in a fine mist. (P. 176.) 



Fifty gallons per acre is not enough spray to iise zchen the 

 plants cover the ground. Every leaf should be coated at each 

 application. When conditions are very threatening, go over 

 the rows a second time in opposite directions, after the first 

 application becomes dr}-. (P. 178.) 



Never omit spraying on account of rainy weather, this is the 

 one time -.i'hoi s[yrayi)ig is most needed. (P. 178.) 



