BLIGHTS OF CONIFEROUS NURSERY STOCK. 11 



established. This method tends to protect the transplants during the 

 period when they have the least absorbing root surface and exposes 

 them to the sun during the larger part of the growing period, so 

 that by the end of the season the trees should be thoroughly hard- 

 ened and ready to stand field planting. Shade will always be a 

 useful adjunct in preventing sun scorch, though the extent to which 

 it should be used will vary greatly with different nurseries. 



Crowding should be avoided in order to avoid sun scorch. What 

 constitutes crowding varies greatly at different nurseries and with 

 different species. At Halsey a second-year seed bed containing 75 

 Scotch pine per square foot is crowded. At Monument 150 Douglas 

 fir per square foot do not crowd each other seriously at the same age. 

 Transplants should be given much more room than seedlings. The 

 older commercial nurseries often practice thinning in their older seed 

 beds and generally give their transplants a great deal of space. Be- 

 cause of the extra cost of weeding and cultivating large areas and the 

 limited space at some nurseries, it is sometimes probably cheaper to 

 crowd stock in a small space and prevent scorch by increased shade 

 or watering. 



Extremely sandy soils should be avoided, and any • deficiency in 

 humus should be counteracted by manure and soiling crops, so as to 

 increase the water-holding power of the soil. Nurseries on very sandy 

 soils in the Northeastern States appear to have more trouble from 

 sun scorch than western nurseries, which have drier climate but 

 somewhat heavier soil. Windbreaks and surface cultivation are also 

 undoubtedly helpful in preventing sun scorch. 



WINTERKILLING. 



Winterkilling is generally understood to mean death as a result 

 of drying when the soil and roots are so frozen that the amount of 

 water given off from the leaves can not be replaced to a sufficient ex- 

 tent by absorption from the soil. In this way its cause is funda- 

 mentally the same as that of sun scorch, the difference being that it 

 occurs while the soil is frozen. Alternate freezing and thawing is 

 considered important in bringing about damage. This may be due 

 simply to the increased loss of water from the needles during warm 

 periods which do not last long enough to thaw out the soil materially. 

 In the West, the warm winds known as " chinooks " produce such 

 sudden very warm periods in the midst of the coldest weather that 

 not only small plants but even the largest forest trees ai*e sometimes 

 killed. 1 ' 



1 Hedgcock, G. G. Notes on some diseases of trees in our national forests. III. Phy- 

 topathology, v. 3, No. 2, p. 112-113, 1913. 



Hartley, Carl. Notes on winterkilling of forest trees. Forest Club Annual [Uni- 

 versity of Nebraska], v. 4, p. 41-46, 1912. 



