JOINTWORM FLIES. 25 



cates that there is small hope of destroying the jointworm by passing 

 infested straw through the manure pile. 



The writer has been experimenting for the past three years in 

 plowing under wheat stubble for the purpose of observing the 

 effect on infestation the following year in wheat planted on the same 

 ground. This work was done in the vicinity of Charlottesville, 

 Va., where no infestation occurred nearer than 5 or 6 miles. There- 

 fore the data secured should be reliable, as there was no opportunity 

 for the jointworm to come in from neighboring fields. Small plats 

 were used and the infestation was accomplished by bringing in a 

 very large amount of infested stubble from a distance, placing it in 

 the growing wheat, and allowing the adults to emerge and infest 

 the plat. In order to insure heavy infestation, large amounts of 

 badly infested stubble were brought in again from a distance after 

 the wheat was cut, making accurate counts of the number thus 

 brought in, and then carefully estimating the infestation that already 

 existed on the plat. The total number of wheat stems or stubbles 

 was then counted on several representative square yards of the plat. 

 In this way the percentage of artifical infestation could be deter- 

 mined accurately. The infested stubbles which had been introduced, 

 together with the stubbles already standing on the plat, were then 

 turned under. The ground was plowed as soon after harvest as 

 possible, disked, and some crop like peas or soy beans sown. The 

 plat was disked again in the fall at the proper time and reseeded to 

 wheat. In this way an 8 per cent infestation was reduced to 1 per 

 cent the following year. A second trial reduced the infestation from 

 32 per cent to 3 per cent. A third trial in 1918 reduced a 19 per 

 cent infestation to 2 per cent. 



These experiments indicate that plowing under stubble is a very 

 effective remedy. It doubtless would destroy all of the insects if 

 all of the infested stubbles could be completely buried, but it is im- 

 possible to do this. Nevertheless it is practicable to control the 

 ravages of the species in this manner. Wliile this method of con- 

 trol would necessitate a change in the existing rotation of crops 

 where wheat is used as a nurse crop for clover, it would seem that it 

 should be adopted if millions of dollars could be saved every year 

 in this manner. Some agronomists admit that it would be prac- 

 ticable to change the existing system of rotation so as to permit 

 plowing down stubble to suppress important insect pests. If this 

 were done not only the jointworm but also the Hessian fly would 

 be controlled, and thus two of the major insect pests of wheat would 

 be largely shorn of their power for harm to our most valuable bread 

 grain. 



