20 BULLETIN 44, U. S. DEPARTMENT OF AGRICULTURE. 
that imported stock will bring in serious tree diseases make it espe- 
cially important that methods of controlling these blights be found. 
in order to encourage the growing of planting stock in this country. 
The writer has not only experimentally determined the cause and 
distinguishing features, but also the control methods for sun scorch, 
the most serious of these blights, and by following his recommenda- 
tions the disease has been controlled in nurseries where it had 
before done serious damage. Distinguishing characters and pre- 
ventive measures for the two other commonest blight types, winter- 
Inlling and mulch injury, have also been determined. An account 
of what the writer has been able to learn from his own work and the 
experience of others with the other types of blight is also given. 
Distinguishing characters and control methods have not been found 
for all of the types. 
It is seldom that a case of nursery blight can be diagnosed merely 
by examining a few specimens of diseased trees. It is hoped to carry 
this investigation so far that each nurseryman will be able to identify 
for himself, by general observations, all of the types of blight which 
attack his nursery beds and to take the necessary steps for preventing 
further losses. 
The writer wishes to acknowledge his indebtedness to Mr. W. H. 
Mast and Mr. R. G. Pierce for their cooperation in the work at the 
Halsey nursery, to Dr. H. L. Shantz for helpful advice, and to Dr. 
Perley Spaulding, under whose general direction the work was con- 
ducted, for advice and the use of his specimens and unpublished 
data. 
SUMMARY. 
The following are the types of blight most likely to cause losses 
of coniferous nursery stock in the United States: 
(1) Sun scorch.—This is the commonest summer trouble. The 
roots die before or at the same time as the tops. Death is caused 
by excessive water loss. It usually occurs when the air is hot and 
dry and the soil around the roots is dry. The disease is worst on 
sandy soils, in crowded beds, and on raised parts of beds. On 
sandy soils it may kill suddenly and in definite patches. Successful 
preventive measures tested by the writer are watering, shading, and 
avoidance of crowding. In nurseries located on mineral soils the 
humus content should be increased. 
(2) Wenterkilling—The tops of the plants dry out when the soil 
is frozen so that the plants can not take up water. The preventive 
measures most used consist of a hght straw mulch on the beds and 
windbreaks. 
(3) Mulch injury—rThe tops die in winter as a result of being 
mulched. This happens while the mulch is still on, or occasionally 
