REPORT OF THE HORTICULTURIST 127 



SESSIONAL PAPER No. 16 

 SPRAYING POTATOES WITH BORDEAUX MIXTURE FOR THE PREVENTION OF LATE BLIGHT AND ROT. 



Experiments with Bordeaux mixture for the prevention of late blight and rot were 

 begun at the Central Experimental Farm in 1892, and from time to time since the 

 results have been published. The value of spraying has been so well proven by the 

 experiments conducted here and in many other parts of this and other countries that, 

 if it were not for the large number of persons who every year grow potatoes for the first 

 time, it would not be necessary to demonstrate the value of spraying. In 1910, rot 

 was very bad where potatoes were not sprayed, and the following experiment shows 

 most strikingly the value of spraying. In one plot, the potatoes were sprayed with an 

 insecticide only, namely, Paris green in the proportion of eight ounces to forty gallons 

 of water. Another plot was sprayed with Bordeaux mixture and Paris green on June 

 27, July 9, July 26 and August 11. At the last spraying, no insecticide was used. An- 

 other plot was sprayed with Soda Bordeaux (Burgundy mixture) and Paris green on 

 the same dates, and a fourth plot with Paris green only until August 2, when 

 Bordeaux was used for the first time. A second application of Bordeaux was 

 given on August 11. Each plot in this experiment was one-forty-fourth of an acre 

 in extent. The potatoes were planted on May 17, and dug on October 15. 



Yield per acre. 

 Bush. Lbs. 



Not sprayed with Bordeaux mixture 117 20 



Sprayed with Bordeaux mixture 234 40 



Not sprayed wtih Bordeaux mixture until August 2 . . 200 12 



Sprayed with Soda Bordeaux (Burgundy mixture) .... 190 18 



This experiment shows that, in years like that of 1910, it will pay well to spray 

 even as late as August 2, but it is advised to begin spraying with Bordeaux mixture not 

 later than July 15, and it is wiser to begin even with the first spraying for the Colorado 

 Potato beetle, in order to protect the plants from the flea beetles, as the edges of the 

 holes in the leaves made by these insects are places from which the Late Blight spreads, 

 and it has been found that Bordeaux mixture prevents much injury from them. 



POTATOES CHANGE OF SEED. 



The results obtained from growing potatoes from Nappan, Nova Scotia, for com- 

 parison with seed potatoes grown at Ottawa, which were published in the annual reports 

 for 1909 and 1910, were so striking that, in 1910, seed was obtained from the Experi- 

 mental Farm, Indian Head, Sask., with the remarkable results given in the table. The 

 dlustration in this report shows the great difference, in the size of the tops of the 

 potato plants, between the Ottawa seed and the Indian Head seed. The vines from the 

 latter seed made a quick, vigorous growth and, when the drought came in the latter 

 part of June and through July, the roots were well down and thus able to withstand 

 it better than those which had made slower and weaker growth. Seed potatoes from 

 parts of the country or possibly even from particular soils where the plants grow com- 

 paratively late, have more vitality or vigour than those which have been grown where 

 the growing season is shortened by hot weather and severe droughts which cause a 

 drying-up of the tops and check the development of the tubers. The potatoes in this 

 test were planted on May 17, 1910 and dug on October 13. 



