POTATO DISEASES IN I907. 303 



sufficient. In a season like the past, 5 or even 6 are necessary. 

 More frequent and thorough spraying is necessary for early 

 blight, and it must as a rule be begun quite early in the season. 



Therefore, unless one has made a careful study of the differ- 

 ent blights, and the relation of their development to weather 

 conditions, the following rule is probably the only safe one to 

 follow : Begin when the tops are 6 or 8 inches high and spray 

 every 10 days (every week if the weather is very cloudy and 

 rainy) until the last of August or the first of September. In 

 any event spraying must be begun some days before the average 

 observer will detect blight on the leaves. Do not stop for rainy 

 weather, this is just the time when spraying is most needed. 

 Each application should be made as often as it is necessary 

 regardless of the weather. If the mixture is properly prepared 

 and it once dries on the leaves, which usually takes place in an 

 hour's time, it will withstand much more washing than is com- 

 monly supposed.* 



In the sense of the term used, properly prepared bordeaux 

 consists of 50 gallons of water, 5 pounds of copper sulphate, 

 and 5 pounds of fresh stone lime (some are using ground or 

 hydrated lime with apparent success). The copper sulphate 

 should be dissolved and the lime slaked in different vessels. 

 Each solution should then be diluted with half of the water 

 and then the cold, dilute sulphate and milk of lime solutions 

 quickly united and thoroughly mixed. Never pour the con- 

 centrated solutions together as an inferior mixture is sure to 

 result. If it is desired to increase the amount of copper sul- 

 phate used per acre, do not make a stronger mixture but increase 

 the number of nozzles per row or go twice over the piece in 

 opposite directions on the rows, provided in the latter case that 

 the nozzles are so arranged as to cover the entire width of the 

 row at each application. 



Most large growers use stock solutions of lime and copper 

 sulphate. The most convenient plan for this is to slake 160 



* The writer has specimens of leaves taken at Foxcroft, October 5, 

 1907, which are well coated with bordeaux mixture, yet they were col- 

 lected 38 days after the last spray was applied. At Orono during this 

 period rain fell on 21 different days making a total of 6.66 inches. 2.18 

 inches of this fell in 24 hours. The two places are not over 40 miles 

 apart by air line and it is believed that the rainfall did not vary materially. 



