20 DISEASES OF ECONOMIC PLANTS 



itself. It finds prominent application with the powdery 

 mildews. The chief applications used are : — 



A. Liver of -sulphur. 



B. Bordeaux mixture. 



C. Ammoniacal copper carbonate. 



D. Flowers of sulphur. 



3. Killing superficial fungi hibernating upon the bark 

 of the dormant plant or plant supports. — Examples : apple 

 hypochnose, peach curl. For this purpose Cleansing 

 Sprays, often called dormant sprays, may be used. 

 Since the parts of the host receiving the spray are highly 

 resistant to their poisonous action, the sprays thus em- 

 ployed may be much stronger than could be safely used 

 when the plant is in foliage. For this purpose use : — 



A. Copper sulphate with hme sufficient to color. 



B. Lime-sulphur mixtures. 



4. The use of protective sprays. — Examples : grape 

 black rot, apple scab. A protective spray is one applied 

 to the plant upon its bark, foliage, or fruit, to kill any 

 offensive germs that may fall upon its surface, or to pre- 

 vent their growth upon or into the plant. Such sprays 

 are distinguished from the cleansing sprays, which are 

 not primarily for protection against future invasion, but 

 rather for the purpose of cleaning off or kiUing all 

 spores actually upon the plant. Protective sprays are 

 usually employed when the plant is in foliage, and there- 

 fore must be used with due regard to the susceptibility 

 of the plant to the poison employed. The protective 

 spray should be applied : — 



1 . Often enough to replace any previous protective spray 

 that may have been removed by rain or other means. 



