432 MANUAL OF FRUIT DISEASES 
of the resulting particles as in lime-sulfur. Other substances 
having adhesive qualities are often added to assist in holding 
the fungicide in place on the host surface. Iron-sulfate and 
arsenate of lead act in this way when added to lime-sulfur. 
The cost of the fungicide is often a limiting factor. A sub- 
stance ideal as a fungicide in every other respect may cost more 
than is warranted by the profits realized from its application. 
Under average conditions, however, this is rarely the deter- 
mining factor: 
The ease with which a fungicide may be applied or the sim- 
plicity of the operations involved are of much importance in 
determining its general and effective use. The ease and rapidity 
with which dust fungicides may be applied in contrast to the 
slow and laborious application of liquid sprays will have much 
to do with the substitution of spraying by dusting. 
Types oF FUNGICIDES 
The fungicides used on fruits are of two general types, de- 
pending on the active principle in each: the copper fungicides 
and the sulfur fungicides. Although there are a number of 
kinds of each, bordeaux mixture, ammoniacal copper carbo- 
nate and water solutions of copper-sulfate are the copper 
forms usually used against fruit-diseases; while lime-sulfur, 
self-boiled lime-sulfur, soda-sulfur compounds and _ finely 
divided sulfur-dust are the usual forms of sulfur fungicides 
employed. - 
So far as fruits are concerned, it may be said that, in general, 
copper fungicides are always to be used on American grapes 
and are safe on sour cherries, gooseberries, currants, pears, 
quinces, strawberries and, in_dry seasons, on apples. Sulfur 
fungicides alone may be used on peaches, plums and sweet 
cherries, and are also safe and effective on European grapes, 
apples, quinces, pears, cherries, currants and gooseberries. 
