REPORT OF TEE HORTICULTURIST 131 



SESSIONAL PAPER No. 16 



SPRAYING POTATOES TO PREVENT BLIGHT AND ROT. 



In 1906 the potatoes were sprayed as usual with Bordeaux mixture and other 

 fungicides to prevent and control the blij^ht and rot. Owinj? to the extremely hot 

 and dry weather which caused the foliage to scald and dry up, and to the presence of 

 aphis in large numbers the foliage v.as so injured that Bordeaux mixture could have 

 little effect, and as the results would be very misleading it has been thought best not 

 to publish them. It may be worth re-peating here, however, that for an average of 

 four years previous to 1906 potatoes sprayed with Bordeaux mixture gave an average 

 yield of 310 bushels 20 lbs. per acre, while those not sprayed with Bordeaux mixture 

 only yielded at the rate of 217 bushels 49 lbs. per acre, a difference of 92 bushels 31 

 lbs. per acre. At 45c. per bushel this means an average increase in value for four 

 y(>ars of $41.62. Enough in one year to buy a good spray pump and pay for the seed 

 that would be used for tlic next crop. 



POTATOES — TEST OF RESISTANCE TO BLIGHT AND ROT. 



It has been known for a long time that Bordeaux mixture will control the blight 

 and rot disease of the potato if spraying is thoroughly done, and the foliage kept 

 covered with the mixture from about the middle of July to the end of the season. 

 Unfortunately, it is difficult to get farmers to spray and as a result the loss from 

 bligjit and rot is very great in some parts of Canada. 



It is important, therefore, to know which varieties will withstand the blight best 

 so that if farmers will not spray they will at least plant the varieties that will give 

 them the best yields without spraying. For a number of years notes have been talven 

 at the Central Experimental Earm of the varieties of potatoes which remained green 

 longest, thus indicating their relative resistance to blight. A list of ten of the varie- 

 ties found most resistant was published by the writer in Bulletin TvTo. 49 on Potato 

 Culture. As none of the varieties there mentioned are absolutely bligbt proof it seem- 

 ed important to find out if their resistance to blight can be increased by selection and 

 with this object in view thirty-two varieties were planted in 1905. 



The tubers from the most productive hills of fourteen of the moat blig-ht resist- 

 ant varieties for that year were kept separate, each hill being dug individually at first 

 and then the tubers from these best hills were mixed and stored together. Of seven of 

 these varieties enough seed was saved from the hills that were left to plant this year 

 for comparison with the potatoes from selected hills. The results, which are striking, 

 are given in the table below. 



These potatoes were not sprayed with Bordeaux mixture or any other fungicide^ 

 but were sprayed with Paris green to preserve the foliage from the potato beetles. 



In addition to the seven varieties tested for comparison with those from unselected 

 seed twenty-four other sorts were tested, seven of which were from selected hills in 

 1905. The best hills of most of the varieties in this test were again kept separate this 

 year. 



It is interesting to note that the varieties which stayed green longest were not in 

 all cases the best croppers. 



The potatoes for this test were planted on May 23, and dug on October 10. They 

 rpceived thorough cultivation, but owing to the extremely dry summer the yields are 

 much less than they otherwise would be. 



10— H 



