INSECTS, DISEASES, AND INJURIES 141 



cause their greatest damage under moist conditions. Control 

 measures should, therefore, aim at the destruction of these 

 fungi in the soil and at the regulation of the surface moisture 

 in the seedling beds. In the case of coniferous seedlings, the 

 application of sulfuric acid has proved the most satisfactory 

 eradication measure, but in applying it attention must be 

 paid to the physical character and natural acidity of the soil. 

 An average strength for use is three-sixteenths of a fluid ounce 

 of clear commercial sulfuric acid to one quart of water (1 

 part of acid to 170 parts of water), this amount being applied 

 to each square foot of soil immediately after the seed is sown. 

 In the case of open porous soils, from which surface evaporation 

 is rapid, it will be necessary to water the beds once or twice 

 a day to prevent acid injury to the roots. In using this method, 

 it is advisable for the grower to make individual tests on his 

 own soil in order to arrive at the most suitable strength. In 

 addition to preventing damping-off, sulfuric acid will also 

 keep down weeds and cause increased vigor in the seedlings. 



Soil alkalinity seems to favor the disease so that the addi- 

 tion of lime and wood-ashes as fertilizers should be avoided. 

 Unrotted stable manure is also likely to increase the loss 

 from this disease. 



The surface moisture and temperature may be effectively 

 controlled by inclosing the beds with upright wire-mesh 

 screens and placing laths across the top. These laths may be 

 removed when the surface becomes too moist or replaced to 

 give the required amount of shading. If this does not result 

 in sufficient drying out of the surface, coarse dry sand may be 

 scattered over the bed. 



As the crowding of seedlings is an important factor in the 

 spread of the disease, broadcast sowing is recommended.* 



♦Hartley, C. Damping-off in Forest Nurseries. U. S. Dcpt. Agr. Bull. 934: 

 1-99. 1921. 



