216 ANNUAL EEPOETS OF DEPARTMENT OF AGEICULTURE. 



past fall and spring to the investigations of the details of fumigation 

 as at present practiced by nurserymen, with the view of standardiz- 

 ing the process. Purchasers of trees often complain of the ineffective- 

 ness of fumigation in kiUing insects, especially the San Jose scale, and 

 of injury to the trees by the treatment. The apple leaf hopper, 

 which infests orchards and nurseries,, is also under investigation. 



Cranberry insects. — Work with cranberry insects in New Jersey 

 has been continued, and material progress is being made. The 

 abundance of the black-headed cranberry worm has offered opportu- 

 nity for large-scale reflowage experiments. It was found that most 

 effective work could be done in destroying the black-headed worm if 

 the plants were submerged for a period of 4 or 5 days when the 

 insects were mostly in the pupal stage. Such treatment was found 

 not to be injurious to the plants. Arsenicals and kerosene sprays did 

 not prove effective in the control of this species, though a nicotine 

 spray gives promise of much value. Important facts bearing on the 

 control of the cranberry girdler have also been determined, namely, 

 that the usual fall flooding of vines for 10 days is useless unless done 

 before about October 1. 



SOUTHERN FIELD-CROP INSECT INVESTIGATIONS. 



Investigations of southern field-crop insects were continued, as in 

 former years, under the direct charge of Mr. W. D. Huntsr. 



Cotton insects. — The principal past considered in relation to 

 cotton culture was the boll weevil. During the year the work on 

 this insect was reorganized to constitute a more intensive investi- 

 gation. It was also necessary to add to the force to enable the 

 bureau to meet the demand for the specific information regarding 

 local weevil conditions that is required by the demonstration service 

 of the department. 



The annual dispersion of the boll weevil in the fall of 1915 assumed 

 unusual proportions, due to the tropical storms. Very extensive 

 areas were newly infested in Florida, Georgia, Alabama, and Ten- 

 nessee, as also in Oklahoma and western Texas. 



The laboratory at Tallulah, La., conducted numerous 3xperi- 

 ments in practical control and made a special study of the local 

 variations in weevil injury. One of the most conspicuous features 

 of the boll-weevil problem is the variation in yield in crops grown 

 apparently under the same conditions. A large number of field 

 examinations were made to determine the cause of this variation. 

 The matter is a complicated one, as soil, subsoil, climatic and other 

 conditions, including the previous cropping of the land, are involved. 

 It is hoped that when this work has been prosecuted for some time 

 it will be possible to determine the exact factors which contribute 

 to the successful production of cotton. The work on direct control 

 measures consists of tests of the value of hand picking of infested 

 squares, and of removing all of the fruit from a plant at the time 

 when weevils are at the lowest ebb in the spring, as well as tests of 

 several mechanical means. The life-history work dealt with the 

 determination of the ability of weevils to hibernate successfully 

 when deprived of food, when fed plants other than cotton, and when 

 fed upon different parts of the cotton plant. Considerable attention 



