2 BULLETIN U, U. S. DEPARTMENT OF AGRICULTUBE. 



tinguishing between blights on the one hand and damping-off and 

 rusts on the other. 



Losses caused by blight are very considerable, nurseries not infre- 

 quently losing practically their entire stock of one or more species of 

 conifers by blight attacks. In many of these cases both the cause of 

 the attack and methods of preventing or stopping it have been en- 

 tirely unknown. No systematic investigation of these blight attacks 

 had been undertaken in this country. In studying the problem the 

 writer since 1909 has visited 31 nurseries which raise conifers and 

 has corresponded with many others. Many different types of blight 

 have been found to exist. By his own observation and experimental 

 work and by bringing together the information obtained from prac- 

 tical nurserymen and from the European literature on nursery dis- 

 eases, the writer has succeeded in distinguishing quite clearly be- 

 tween the most important types of blight and drawing conclusions as 

 to the best preventive measures. In the following pages the causes, 

 distinguishing characters, and preventive measures for all of the 

 types of blight met with are given as fully as the present condition 

 of our knowledge will permit. 



PHYSIOLOGICAL TROUBLES. 



SUN SCORCH. 



Sun scorch is the commonest and most serious trouble in most of 

 the nurseries. By sun scorch is meant the death of entire seedlings 

 or transplants or parts of them, due to lack of balance between the 

 water absorption by the roots and water loss from the needles during 

 the growing season. Stated in a somewhat simpler way, sun scorch 

 is drought injury which occurs in the growing season. The term 

 " sun scorch " has been used by Stone * and others for a similar trouble 

 of conifers in New England forests. Its work in second-year seed 

 beds on sandy soil has been described by Hartig. 2 It will be con- 

 sidered in detail, because in many cases it resembles other diseases so 

 closely as to go unrecognized. For example, sun scorch for several 

 years caused heavy losses in both seedlings and transplants at the 

 Forest Service nursery at Halsey, Nebr., where most of the writer's 

 work on this disease has been done. In a single case the records indi- 

 cated a loss of 70 per cent of all the 2-year-old seedlings of jack 

 pine (Pinus divaricata (Ait.) Gordon) and Scotch pine (P. sylves- 

 •tris L.). The damage looked so little like drought that for some 

 time it was supposed to be due to parasitic fungi, and Bordeaux 

 mixture was employed to control it. Losses from this disease have 



1 Stone, G. 10. Sun scorch of tho pine. Massachusetts Agricultural Experiment Sta- 

 tion, 22d Annual Report, pt. 2 [1900], p. 65-60, 1910. 



2 Hartig, Robert. Lehrbuch der Baumkrankhciten. Aufl. 2, Berlin, 1889, p. 104. 



