2 BULLETIE" 181, U. S. DEPAETMEjI^T OF AGRICULTURE. 



the horer and grown profit aMy on a commercial scale if the locicsts 

 are planted in thick stands or mixed with other trees so as to produce 

 a densely shaded condition and natural pruning during the f/rst 10 

 to 15 years of growth. 



HISTORICAL. 



The great variation in the extent of injury by borers to both 

 planted and natural stands of black locust has been noted by many 

 writers. In fact, a,s early as 1821, Pickering (2)^ stated that trees 

 of natural growth in groves were much less liable to injury than were 

 transplanted trees. Schwarz (3) in 1890 observed that the insect 

 lives in large colonies affecting all trees of small groves, while long 

 hillsides full of locust are not infested. Cotton (5) observed that in 

 Ohio injury was greater in single trees and plantations of consider- 

 able size than in natural forests. Hopkins (6) remarked that " Favor- 

 able conditions for the destructive work of the borer appear to be 

 found in the presence of isolated trees and groves in the open. . . . 

 Unfavorable conditions are found in forest growth or large areas of 

 pure stands, or mixed. stands where the locust predominates; also, in 

 plantations and groves where resistant varieties prevail, and where 

 there is no goldenrod or other favorite food for the beetles." Dear- 

 born (1), Kellogg (4), and Garman (7) also call attention to this 

 fact. 



OBSERVATIONS BY THE WRITER. 



In examining locust plantations during the last few years, the 

 writer was greatly impressed with the absolute destruction of some 

 tracts, while others, or parts of the same tracts, were thrifty and un- 

 manned by borers. This was convincing evidence that the trees 

 could be grown so as not to be injured hj the locust borer. Many 

 tracts, therefore, both planted and natural, were studied with the 

 idea of securing evidence that might be applicable in a practical 

 way. As far as possible the accurate history of many locust stands, 

 both pure and mixed, was obtained and factors that might be respon- 

 sible for the presence or absence of injury were weighed. As a re- 

 sult of such study, it was found that the amount of destruction was 

 unquestionably gTeater in those tracts which had been pruned oc- 

 casionally, closely grazed, or in which fire had gone through from 

 time to time, killing out the underbrush and destroying the natural 

 shade produced by weeds or shrubbery. The denser the growth, par- 

 ticularly weeds and undergrowth about the stem of the tree, the 

 less was the amount of borer work and vice versa. Pure stands in 

 open fields, where the trees were growing from 2 to 3 feet apart, were 

 seldom injured, while near-by isolated trees were riddled by the borer. 



1 Reference is made by number in parenthesia to " Literature cited," p. 12. 



