APPLE POWDERY MILDEW. 23 



retains it at picking time in the fall. Moreover, the control estab- 

 lished by the use of this material did not approach the results ob- 

 tained from the more efficient of the sulphur sprays. 



Self -boiled lime-sulphur offered the same objection as Bordeaux 

 mixture in that heavy deposits of spray material remained on the 

 apples and prevented their proper coloring. It likewise proved less 

 efficient than several of the other materials. It appeared to give 

 some protection to healthy parts after application, but it failed to 

 destroy existing infections, and conidia were abundantly pushed up 

 through the spray coating. 



Ammoniacal copper carbonate closely approximated the fungicidal 

 action of Bordeaux mixture and left no objectionable deposit on the 

 apples. For this reason it is preferred to Bordeaux mixture for use 

 in spraying during hot weather. 



The barium-sulphur preparation appeared to approximate the 

 action of commercial lime-sulphur solution against mildew, but it 

 proved more toxic to fruit and foliage during hot weather 



SUMMARY OF CONTROL MEASURES. 



The results noted demonstrate — 



(1) That sulphur sprays are superior to Bordeaux mixture or ammoniacal 

 copper carbonate for mildew control. 



(2) That, except, possibly in seasons of exceptionally heavy infection, apple 

 powdery mildew can be commercially controlled by sprays applied before 

 hot weather starts and consequently before there is danger of sulphur 

 spotting of the fruit. 



(3) That while Bordeaux mixture and ammoniacal copper carbonate may be 

 less efficient as control agents than lime-sulphur solution or other sulphur 

 sprays, their use may be advisable in years when continued spraying may 

 be necessary. 



(4) That ammoniacal copper carbonate is preferable to Bordeaux mixture for 

 this purpose, since it does not leave an objectionable deposit on the fruit 

 and thereby prevent normal coloring. 



(5) That in the case of sulphur sprays efficiency is dependent on (a) the im- 

 mediate caustic effect of the sprays on the fungous coating and (&) the 

 deposit of a protective coating of free sulphur over noninfected areas. 

 Both a and & are largely dependent on the spreading qualities of the sprays, 

 which, in turn, are dependent on the surface tension and the interfacial 

 tension of the sprays. 



DORMANT SPRAYS. 



A possible influence of winter or dormant sprays of strong lime- 

 sulphur solution on the overwintering fungus has been suggested, but 

 these experiments do not point to any such influence. Each year 

 just after the buds had begun to swell, but before the appearance of 

 the first leaves, the check trees were thoroughly sprayed with lime- 

 sulphur solution at a strength of 3^° Baume. These trees always 



