4 BULLETIN U, U. S. DEPARTMENT OF AGEICULTUEE. 



occur in such distinct patches; and if any part of a transplant is 

 affected, either an entire branch or the entire plant dies at once. 



A feature of sun scorch in nurseries, as well as in the older trees 

 described by Stone, 1 is that the absorbing portions of roots die at the 

 same time as the tops or even before. This indicates that the leaf 

 and stem tissues can stand water loss better than the vegetative 

 tissues of the roots. Especially in the case of transplants the cam- 

 bium of the entire root system, or at least of the outlying portions 

 of it, has been found to be dead and brown. By the time the needles 

 show the first signs of yellowing, a large part of the root cambium is 

 already gone. This especially early death of a large proportion of 

 the root systems of the scorched transplants is probably due to the 

 fact that a tree in the transplant bed has a smaller root system in 

 proportion to its transpiring surface than a second-year seedling 

 would have. When only a part of the needles on a plant are killed 

 it appears that the damage to the root is more extensive than to the 

 tops. This is indicated by the fact that a plant which has lost part 

 of its needles in an attack of this disease is more likely to succumb 

 to later attacks of the same nature. Evidently the reduction in 

 transpiring surface caused by the first attack is more than counter- 

 balanced by the reduction in absorbing surface. 



During several sun-scorch attacks at Halsey, and at two or three 

 other times when the weather was hot and dry but no actual sun 

 scorch had occurred, a peculiar type of injury appeared on young, 

 growing shoots of second-year pine seedlings. White, shrunken, 

 watery-looking patches appeared on the green stems rather suddenly, 

 followed by the death of the plant beyond the point attacked. A 

 very similar " white-spot " injury, occurring near the bases of the 

 stems of seedlings less than a month old at the Halsey nursery, arid 

 which has often been confused with damping-off, can be controlled 

 by shading and watering. While a parasite may be in some way 

 concerned in causing the trouble in both ages of stock, there is little 

 doubt that drought and possibly also excessive light or heat working 

 independently are mainly responsible. This white-spot injury to 

 second-year seedlings is included under sun scorch because it often 

 occurs simultaneously and can be prevented by the measures which 

 prevent scorch. It is not important. 



EVIDENCE AS TO CAUSE OF SUN SCORCH. 



The conclusion that the disease is due to disproportionate water 

 loss is based on the following facts: 



(1) Spraying with fungicides has failed to control the trouble. 

 While spraying experiments have not been exhaustive, Bordeaux 



1 Stone, G. E. Sun scorch of Hie pine. Massachusetts Agricultural Experiment Sta- 

 tion, 22d ADnual Report, pt. 2 [1909], p. 65-69, 1910. 



