OIDIUM OR POWDERY MILDEW OF THE VINE. 347 



a spray is used it should therefore be followed by an application of dry 

 sulfur to complete the work. 



The sprays which have been found most effective for this purpose 

 are Bordeaux mixture, permanganate of potash, and alkaline polysul- 

 fids. Vines are not easily injured by copper salts, so that a strong 

 Bordeaux can be used. The 6-4-50 formula would be suitable. 



Permanganate of potash at the rate of one pound to 100 gallons of 

 water has been found effective. A little chloride of potash or common 

 salt improves the spray by increasing its adhesive qualities. 



Liver of sulfur at the rate of 4 pounds to 100 gallons of water with 

 4 pounds of soap has also been used with success. Alkaline polysulfids 

 have also been used effectively in the same way. These sprays are more 

 permanent in their effects than the copper and permanganate mixtures 

 because a small amount of finely divided free sulfur is set free, which 

 acts in the same way as the powdered sulfur when applied in the usual 

 way. It is very probable that a weak lime-salt-sulfur spray such as is 

 in common use on fruit trees would be equally effective. 



WINTER TREATMENT. 



As the fungus passes the winter, when it has no green leaves to 

 grow on, in the form of resting spores on the canes and in the soil and 

 perhaps of resting mycelium under the bud scales, it has been sug- 

 gested that a winter treatment which would destroy these hibernating 

 forms would be the best method of control, or at least that it would 

 much simplify the summer treatment. 



The methods usually proposed are to spray the vines after pruning 

 with the lime-salt-sulfur used for fruit trees or with a 2 per cent, solu- 

 tion of bluestone. Others advise swabbing the vines at the same time 

 with a saturated solution of iron sulfate (copperas) acidified with 1 

 per cent .of sulfuric acid. To make the treatment more thorough, some 

 remove all the dry bark of the vine by means of scrapers before treat- 

 ment. This is supposed to destroy all the perithecia on the vine. In 

 order to prevent infection from the hibernating mycelium under the 

 bud scales it is further advised to spray the vines with Bordeaux mix- 

 ture just as the buds swell in the spring. 



Such treatments as these are of course very expensive and cost 

 more than several sulfurings, so that, unless they can be proved to be 

 effective, they should not be adopted. There is considerable evidence 

 that such treatment makes the vines more vigorous and healthy, but 

 that it has any effect on controlling the Oidium is doubtful. It seems 

 unnecessary, because if we control the Oidium in the summer, as we 



