32 PROTECTION OF PLANTS — 1922-23 



The Comparative Susceptibility of Mcintosh and Fameuse Apples to Late 



Attacks of Scab. 



I have usually considered that there was not much difference in the suscep- 

 tibility of Mcintosh and of Fameuseapples tothisdisease,bothbeingwellknown 

 to be very susceptible I am still unable to say whether there is any difference in 

 their susceptibility to early attacks of the disease, because ordinary spray mix- 

 tures if properly applied will control the scab on either variety; but this year 

 in a ten acre orchard consisting of alternate row of Mcintosh and Fameuse I 

 discovered a distinct difference in the degree of susceptibility to late infections. 



The whole orchard received the regular three sprays and in addition part of 

 each variety received a fourth. On both Mcintosh and Fameuse the scab was 

 fairly well controlled in the early part of the season, there being an average of 

 slightly over 79c on the Mcintosh and slightly under 7% on the Fameuse. As 

 check ^Mcintosh trees lost every apple and had most of their early leaves des- 

 troyed by the scab the year was clearly very favourable for the disease. After 

 the first of July a late infection began in the orchard due to wet weather the 

 last week in June and also later in the season. Under these conditions I was 

 surprised to find that the Mcintosh proved much more susceptible to the di- 

 sease, the total late scab on Fameuse being 24.2% and on Mcintosh 66.6%; 

 that is, Mcintosh were nearly three times as badly affected as Fameuse under 

 exactlj" the same conditions of weather, soil and situation. This is a striking 

 difference and the conclusion one is forced to draw is that we must use more vigi- 

 lance in a wet season to keep Mcintosh free from disease than Fameuse. 



When Shall we Apply the First Spray to Apple Trees? 



A very important question is — When should we apply the first spray in 

 apple orchards in which there is no San Jose Scale and not much Oyster Shell 

 Scale or Blister Mite ? — a condition which must be common in Quebec. 



A study of the life-history of the fungus would indicate that there is little 

 value in spraying for this disease before the buds burst and that we should wait 

 at least until the bursting has taken place and green tissues are exposed to infec- 

 tion. But there are green tissues exposed to infection from the time the buds 

 are bursting until the regular pinks pray is applied just before the blossoms open ; 

 moreover, as the leaflets keep increasing in size during this period and the blos- 

 som bud clusters begin to push forth towards the end of it, it is impossible for 

 any single application, no matter when applied, to give complete protection 

 throughout the period. 



