EXPERIMENT STATION BULLETINS. 269 



Spraying experiments for blight have also been carried on in Rhode 

 Island,* and in Ohio,t and in each case a marked increase in yield 

 was noted. 



These experiments from other states show that spraying for late 

 blight pays there. Why should it not pay here in Michigan? 



V. DIRECTIONS FOR SPRAYING. 



Spraying for late blight should commence when the plants are about 

 12 inches high and should be repeated at intervals of 10 to 20 days, de- 

 pending greatly upon the season. If the season should happen to be a 

 wet one, a greater number of sprayings are necessary than if the sea- 

 son is an ordinary one. Advantage can be taken of the fact that the 

 poison used in combating the potato bugs can be mixed with the Bor- 

 deaux mixture without impairing the value of either, so that when 

 spraying with Bordeaux we can spray for bugs at the same time. 



The Bordeaux mixture should contain at least 5 pounds of copper 

 sulphate to 50 gallons of the mixture. The writer recommends the 

 following formula for the Bordeaux mixture for use on potatoes: Five 

 pounds Copper Sulphate, 6 pounds Stone Lime, to 50 gallons of water. 

 These quantities are not arbitrary and doubtless many other combina- 

 tions of the lime and copper sulphate can be used with success. 



In order to get results, the Bordeaux mixture must be well applied 

 and strike every part of the plant. If a crop sprayer is used, one 

 should be selected that will throw the material up against the under 

 side of the leaf and also give a mist-like spray. 



A single spraying will be of benefit, but one must remember that in 

 order to get control of the blight and make potato spraying pay, the 

 Bordeaux mixture must he on the foliage hefore the disease makes its 

 appearance and that the supply must he kept up during the groimng 

 season. 



VI. WHEN SHALL WE DIG BLIGHTED POTATOES? 



The rotting of the stored tubers is one of the most serious phases of 

 the devastations wrought by the blight, and the question is often asked 

 ''Does it make any difference in the rotting if the digging is done be- 

 fore the tojis are dead and dry, or will it pay to wait until they are?" 



This subject has been investigated by Stewart and Eustace of the 

 New York Experiment Station,! who say : "If the tubers hre to be 

 stored they should not be dug until the tops are dead and thoroughly 

 dry, in order that the fungus spores may be given a chance to dry up 

 and die. As long as the tops remain even partially green the spores 

 of the blight fungus continue to live. In the process of digging, the 

 tubers become covered with these live spores and if conditions are at 

 all favorable more or less rot results. This explains why sprayed pota- 

 toes sometimes rot more in storage than unsprayed ones." 

 ' Precautions should be taken after digging not to cover the piles over 



* R. I. Bull. No. 14, p. 187. 



t September bulletin, Ohio Exp. Sta., 1889. 



% Bulletin 264, pp. 202-203 



