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 mildew 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 pruning of trees (a) for the purpose of obtaining the general 
stimulating effects that come from pruning at that time and (6b) 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. 
