TWO EPIDliMICS OF POTATO BLIGHT AXD ROT. 1 79 



to be the case by most people, than one applied during bright, 

 clear weather. However, as previously stated, properly pre- 

 pared bordeaux mixture is remarkably adhesive and will stand 

 considerable washing if once dried on the foliage. Hence, 

 never omit to spray on account of rainy weather, provided the 

 rain stops long enough to apply the mixture and to allow it to 

 dry on. There is often no excuse for the man who loses his 

 crop by blight on account of rainy weather. If everything is 

 in readiness it is a very exceptional season when the rain does 

 not stop long enough to spray at least a part of a field at a time 

 and to allow the spray to dry on after it is applied. ■ 



In 1909 many failures can be traced directly to too few 

 sprayings and in every case investigated the spraying was dis- 

 continued much too early, considering the nature of the season. 

 Large numbers of instances were found where the fields were 

 sprayed but three times and cases where only two or even one 

 application was made were by no means rare. Where these 

 few applications were made, they were invariably made too 

 e?irly in the season, and while they doubtless did some good 

 they were by no means distributed to the best advantage. 



If one thoroughly understands the weather conditions which 

 are likely to produce late blight it is possible to so distribute 

 3 or 4 thorough sprayings in such a manner as to give prac- 

 tically complete protection to the crop in ordinary seasons, but 

 it would doubtless be impossible in such seasons as those of 

 1907 and 1909. If oaly 3 sprayings are made in this section 

 it would usually be best to wait till late in July or the first of 

 August before beginning. However, for the general grower 

 who has not the benefit of long experience or the advice of a 

 trained observer on these points it is unsafe to depend upon so 

 few sprayings in a season. It has been the policy of this 

 Station to recommend that spraying be begun when the tops 

 are 6 to 8 inches high and repeated every 10 days (every week, 

 if the weather is very cloudy or rainy)* until the last of August 

 or the first of September, or later if necessary. In the light 

 of the experience obtained during 1909 the only modification 



* Cases might occur in exceptional seasons when the rains are very 

 heavy and conditions very threatening where two or even three of the 

 sprayings might be made at a less interval between. 



