432 PLANTS AND MAN 



waiting three years before replanting soil areas in which it is 

 known to occur. 



Black scurf or scab of potatoes is produced by another soil 

 inhabiting fungus. This organism attacks tubers, stems, and roots, 

 causing characteristic lesions and interfering with translocation 

 and storage of foods in the tubers. The black scurf fungus also 

 occurs in destructive form on celery, onions, beets, tomatoes, and 

 beans, in all cases affecting mostly the underground plant parts. 

 Control is effected mainly by long rotation of susceptible crops 

 with those not susceptible, such as the cereals. 



Prior to the enactment of the plant quarantine law of 1912, 

 the United States was unprotected against entrance of new insect 

 and fungus parasites of plants. This act provides for regulation 

 of imports of nursery stocks, plants, and plant products, and gives 

 the Secretary of Agriculture the power to establish and maintain 

 quarantine districts for insects and diseases. Had such an act been 

 passed fifty years previous to this date, American forestry and 

 agriculture might have been spared the ravages of such imported 

 diseases as chestnut blight, white pine blister rust, and asparagus 

 rust, as well as such insect pests as San Jose scale, gypsy moth, and 

 the cotton boll weevil. Properly inspected and approved bulbs, 

 seeds, and nursery stocks are still imported from Europe and other 

 foreign countries, so that these quarantine laws have by no means 

 cut us off from the most desirable of the world's flowers and fruits. 



