SEEDLING DISEASES AND INJURIES 11 



Control. 



The most direct and effective measure to insure prevention 

 or control of sun-scorch is heavy watering. The index as to 

 frequency and amount of water to supply may be obtained 

 by examining daily the actual water-content of the layer of 

 soil in which the roots are growing. Light watering at fre- 

 quent intervals may make the beds appear well watered, while 

 actually the water may be lost in evaporation and never reach 

 the roots of the plants in any quantity. 



A great saving in watering and a partial protection from 

 sun-scorch may be easily obtained by erecting lath half-shade 

 screens over the beds. Shading has often been used success- 

 fully to halt further sun-scorch after it has once appeared. 



References 



Hartley, Carl. Tte blights of coniferous nursery stock. U. S. Dept. 



Agr. Bui. 44 : 1-21. 1913. 

 Stone,, G. E. Sun scorch of the pine. Massachusetts Agr. Exp. Sta. 



Ann. Kept. 22 : 2 : 65-69. 1910. 



Winter-Drying 



Caused by the simultaneous occurrence of low soil temperatures and 

 high air temperatures 



Conifers are subject to the death of the whole or part of the 

 tree, during the winter months. The symptoms of winter- 

 drying are similar to -those of sun-scorch, discussed on page 9. 

 The cause is also similar in that a sufficient intake of water to 

 compensate for that lost in transpiration is impossible, because 

 of the frozen condition of the soil. In sun-scorch, sufficient 

 water is not present in the soil and in winter-drying, although 

 the soil is saturated, the water is not available in the form of 

 ice. Consequently when the air is warm, larger quantities of 

 water are lost by the leaves than can be replaced. For a further 

 discussion of this injury to older trees, see page 18. 



