224 MANUAL OF FRUIT DISEASES 
perithecia. The spores come to rest on the young leaves or 
fruits. Following germination of the ascospores a weft of 
mycelium develops which grows superficially. At certain 
places, however, small sucker-like bodies, called haustoria, 
are sent into the host cells; these are the organs of feeding. 
Nourishment is derived from the host and the mycelium grows. 
In the early part of the growing-season summer spores are 
formed. They are produced in chains on erect branches sent 
up from the weft of surface mycelium. The conidia (spores) 
are produced in great numbers, and soon fall away, giving the 
lesion a dusty or powdery aspect, whence the name powdery- 
mildew. The conidia are scattered by the wind, and they give 
rise to new infections similar to those just described. Toward 
autumn the perithecia are formed, and these serve to carry the 
fungus through the winter. 
Control. 
This is one of the most difficult of powdery-mildews to con- 
trol, particularly in wet seasons. However, if remedial measures 
are thoroughly applied, less difficulty will be experienced. The 
work may be done at a slight expense. 
The standard remedy has been to spray with potassium-sul- 
fide (liver-of-sulfur), one ounce to two or three gallons of water. 
In New York State and elsewhere lime-sulfur solution, at the 
rate of one to forty, has proven effective. In Oregon it has 
been found that an application of lime-sulfur at dormant 
strength on dormant branches, followed by a solution diluted 
one to thirty, gives excellent satisfaction. It is suggested that 
it may be desirable to use potassium-sulfide in later applica- 
tions, since lime-sulfur leaves a deposit on the sprayed ‘parts. 
The applications of a fungicide should be made as follows: (1) 
when buds break open; (2) at intervals of ten days until at 
least five applications have been made. The more susceptible 
varieties may demand more sprayings. 
Pruning in the fall may reduce the amount of the inoculum, 
