348 SEEDING AND PLANTING 



harm done, due to the large number of white grubs and other 

 insects destroyed. When overabundant they are most effectively 

 reduced by trapping. 



3. THE Loss OF PLANTS 



The death of young trees in the seedbeds and transplant beds 

 is usually due to one or more of the following causes: 



a. Adverse weather conditions. 



b. Birds. 



c. Injurious insects. 



d. Parasitic fungi. 



4. Protecting the Nursery from Injury Caused by Adverse 

 Weather Conditions. Losses due to adverse weather conditions 

 are accompanied by marked physiological disturbances in the 

 activities of the plants. The trees turn brown and die, in whole 

 or in part, without a definite symptom to indicate the cause. This 

 condition is known as blight. 1 Losses caused by blight are often 

 excessive, not infrequently the entire stock of one or more species 

 being completely destroyed. The more common and destructive 

 forms of these physiological troubles are sun scorch, winter killing, 

 frost damage, and root rot. 



Sun scorch is due to a lack of balance between the water absorp- 

 tion by the roots and transpiration from the foliage during the 

 growing season. It is most likely to occur in dense stands of 2-year 

 seedlings in midsummer when the ground is the driest and the loss 

 of moisture through transpiration the greatest. In serious cases of 

 sun scorch the trees are killed outright, usually in large patches 

 through the middle of the beds. In less serious cases only the 

 terminal bud and the leaves are affected. The leaves rapidly 

 lose their green color, become straw-colored and finally deep 

 brown. Sun scorch is sometimes very harmful in transplant beds 

 of conifers after they have begun their growth. If weather condi- 

 tions cause excessive water loss which the roots cannot supply, the 

 browning of the foliage occurs and the plants die. The loss in 

 transplant beds, however, does not occur in distinct patches as in 

 the seedbeds. The trouble is most common on very light, sandy 

 soils which during droughts are quickly reduced to a low water 

 content. Sun scorch is entirely prevented by the thorough watering 



1 Hartley, C.: The blights of coniferous nursery stock. (U. S. Dept. of 

 Agr., Bui. 44. 1913.) 



