16 BULLETIN 120, U. S. DEPARTMENT OF AGRICULTURE. 
This operation of washing the precipitate should be repeated until 
the water poured off no longer shows the yellow lime-sulphur tinge. 
Probably three or more such washings will be required, depending 
upon how careful the operator has been in using only a slight excess 
of lime-sulphur solution. 
It is evident that the preparation of this stock supply should be 
commenced two or three days before the spraying is to be done, but 
when once prepared it may be kept indefinitely. If care is used in 
weighing out each lot of iron sulphate and if the lime-sulphur solu- 
tion used is accurately measured there will be no trouble in making 
up the stock supphes rapidly after the first two or three batches 
have been prepared, and it will be remembered that each batch is 
sufficient for making 500 gallons of spray mixture. In order to keep 
a supply of the stock mixture on hand, several batches should be 
prepared before the spraying commences, and as rapidly as a barrel 
is emptied the preparation of a new batch should be started. Iron 
sulphate is comparatively cheap, and the entire cost of materials for 
preparing 100 gallons of the mildew spray, when diluted according 
to the recommendations given in this bulletin, should not exceed 15 
or 20 cents. 
When the washing has been completed, the stock barrel should be 
filled with water to exactly 50 gallons. The material is now ready 
for use as directed under “* General formula for the spray mixture,” 
on page 17, but care should be taken to stir the contents of the barrel 
thoroughly each time before any of the mixture is taken out. 
IMPORTANCE OF EARLY SPRAYING. 
Attention has been called to the fact that the apple foliage is sub- 
ject to mildew attack shortly after it begins to come out in the spring. 
The serious fruit dropping that may result from delaying the first 
application until after the frutt is an inch or more in diameter has 
Leen discussed, and attention has been called to the possibility of 
developing sulphur immunity or resistance to injurious sulphur 
effects by beginning the spraying early and repeating it at intervals 
of two to three weeks. Also, it has been stated that these sulphur 
sprays have a distinct stimulating effect on foliage growth and that 
the mildew is more readily controlled on vigorously growing trees. 
Thus there are a number of reasons for making the first spray apph- 
cation early in the season, namely, to protect the very early foliage 
from mildew, to develop immunity to sulphur injury and thus avoid 
serious fruit dropping later in the season, and to bring about sul- 
phur stimulation, thus inducing a vigorous early growth of foliage. 
Furthermore, it has been found that precipitated sulphur acts as a 
restrainer of the arsenical foliage injury that in the Pajaro Valley 
