26 BULLETIN 120;, U. S. DEPARTMENT OF AGRICULTURE. 



It is probable that investigations now in progress will show that 

 in some cases dormant spraying with solutions of nitrate of soda 

 plus caustic soda is more desirable than crude-oil spraying. 



SUMMARY OF CONTROL METHODS. 



By way of summarizing the above conclusions it may be stated 

 that there are three distinct phases of the method of controlling 

 apple powdery mildeAv as outlined in this bulletin: 



(1) Foliage spraying with iron-sulphid mixture, precipitated sulphur, or 

 sulphur in some other very finely divided form. 



(2) Winter priming of trees (a) for the purpose of obtaining the general 

 stimulating effects that come from pruning at that time and (b) directed 

 particularly toward the eradication of mildewed twigs. 



(3) Winter spraying with some spray that has the effect of inducing a 

 vigorous foliage growth in the spring. 



The practice of careful and thorough summer spraying year after 

 year will gradually bring about a much-improved condition of the 

 trees, but for the best results the entire method, as outlined above, 

 must be followed. 



Finally, it will be remembered that the results, statements, and' 

 recommendations recorded in this bulletin are based chiefly on ex- 

 periments and observations made in the Pajaro Valley, in Cali- 

 fornia ; and, because of the somewhat extreme conditions obtaining in 

 that valley, it will probably be found desirable to vary the recom- 

 mendations here given to suit the local conditions and requirements 

 of other apple-growing districts in which the disease may become 

 sufficiently prevalent to require attention. In some sections, for in- 

 stance, summer spraying alone may provide a satisfactory control 

 of the disease, and in certain districts it will probably be found 

 possible to increase the amount of stock iron-sulphid mixture used 

 to each 100 gallons of spray. 



The various effects of sulphur which have been discussed, such 

 as fruit and leaf dropping and stimulation of foliage growth, may 

 not develop as strongly in other districts as they do in the Pajaro 

 Valley, but before attempting to use very much stronger dosages of 

 sulphur than those recommended in this bulletin careful considera- 

 tion should be given to the possibility of causing sulphur burning 

 on the fruit. In any case, it will probably be found necessary to 

 repeat the mildew spraying at intervals of three weeks or less during 

 the entire period in which the trees are putting out new foliage. 



