14 BULLETIN 120, U. S. DEPARTMENT OF AGRICULTURE. 
an opportunity to act on heavy sulphur deposits, the skin and outer 
layers of the flesh became brown and leathery. Mild cases of such 
injury have very much the appearance of ordinary sun scald, but 
when the damage becomes more serious the growth of the affected 
area is checked and the fruit cracks open. This type of injury has 
developed only occasionally, and then only when a strong dosage of 
sulphur or iron-sulphid mixture has been used. No such damage 
has ever been produced by the weak dosages of sulphur that are 
recommended in this bulletin for mildew control. 
When it became evident that the tendency to cause fruit and foliage 
dropping was one of the general properties of these finely divided 
forms of sulphur, attention was turned to the investigation of a large 
number of other materials, in the hope that some substance might be 
found which would prove as effective as sulphur against the mildew 
and yet be free from the injurious property of causing fruit and 
foliage to drop. Among such substances tested, the most satisfac- 
tory results in mildew control were obtained from a number of dye 
materials, Fifty or more commercial dyes and laboratory stains 
were tested, and it was found that a number of them, when apphed 
in water solutions, were capable of staining the mycelium and killing 
the mildew. Such sprays, however, are curative rather than pre- 
ventive in their action, and while, with the exception of eosin, no 
injurious physiologic eflects were pnepumicre dl their sacs prop- 
erties were not entirely satisfactory. 
Meantime, investigations with the iron-sulphid and other precipi- 
tated at hr ‘sprays were continued, and it has been found that by 
using weak mixtures, starting the spraying early, and repeating it 
frequently a very satisfactory mildew control can be obtained without 
danger of causing fruit to drop. Thus, after six years of investi- 
gations, in which 250 or 300 spraying experiments were conducted 
and over 100 different materials tested, sulphur in some very finely 
divided form still remains the most satisfactory fungicide for use 
against apple powdery mildew in the Pajaro Valley. : 
It may be repeated here that those forms of sulphur known com- 
mercially as sublimed sulphur, or flowers of sulphur, sulphur flour, 
and ground sulphur are far too coarse to be effective. Sulphur in 
its colloidal form gives excellent mildew control and possesses some 
distinct advantages of its own, especially in the matter of covering 
power. Certain difficulties involved in its preparation, however, 
prevent the grower from making his own supply. Precipitated sul- 
phur may be made in a number of different ways, but what is here 
called the iron-sulphid mixture is the simplest and a form in 
which the grower can prepare it. 
