February, '17] McCOLLOCH: HESSIAN FLY SPREAD 165 



and one-fourth miles southwest. In other words, here were three 

 conditions which would seem prohibitive to severe fly infestation, 

 namely, late planting, new wheat land, and isolation. The writer 

 had visited this field in December, 1913, and after a thorough investi- 

 gation found no fly. On making the examination in May, 1914, it 

 was found that 90 per cent of the plants were infested, many of them 

 bearing as high as thirty flaxseeds and larvge. The only apparent ex- 

 planation for this heavy infestation was that the adult flies had been 

 carried there by the wind. A badly infested field of volunteer wheat 

 was located one and one-fourth miles directly southwest of this field, 

 and during the period of emergence of the main spring brood of adults, 

 the prevailing wind was from this direction. 



Another example of fly diffusion due to wind is shown in Figure 6 

 of six fields at McFarland, Kansas. This study was made primarily 

 to work out the value of cultural methods of control. The soil and 

 climatic conditions are the same on all these farms and the experi- 

 ment was to determine the value of the destruction of volunteer wheat 

 and late sowing as a means of controlling the fly. On the farms 

 A, D, and C the volunteer wheat was destroyed and the planting de- 

 layed until the fly-free date. Field F was in wheat for the first time, 

 the preceding crop being alfalfa. On farms B and E little effort was 

 made to destroy the volunteer wheat and planting was ten days 

 before the fly-free date. Fields B and E were heavily damaged in the 

 fall, while repeated search in fields A, D, C and F from November to 

 April failed to show any appreciable fly infestation. After the emer- 

 gence of the spring brood in April, however, eggs were found in large 

 numbers over most of the shaded area. These fields were watched 

 until harvest, at which time fields B and E were practically ruined. 

 Field C was rather heavily infested and the northwest part of field D 

 suffered severely. The southeast part of field D came through prac- 

 tically free from injury and fields A and F suffered no injury whatever. 

 .It is interesting to note that there was practically no injury along the 

 east side of field D, although it joined one of the worst infested fields in 

 the neighborhood. A comparison of the yields in these fields will show 

 the true amount of Hessian fly injury. 



45 bushels per acre 



3 to 5 bushels per acre 

 25 bushels per acre 



NW 25 bushels per acre 

 SE 40 bushels per acre 



4 bushels per acre 

 45 to 48 bushels per acre 



Evidence that the wind is an important factor in the dissemination 

 of fly is brought out in these fields. During the time the main spring 



