1S6 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 9 



But even if repeated cultivations are give with the ordinary disk 

 harrow, some. volunteer wheat and much blue joint grass is very likely 

 to escape and only a few such plants are necessary to bring about an 

 infestation of wheat aphis in localities where it is abundant. Moreover, 

 in the most heavily infested districts of Fergus County, soil and climatic 

 conditions are such that frequent diskings during the summer months 

 are not desirable, for when the soil becomes finely pulverized it blows 

 and drifts badly the following winter. Several of the less common 

 methods of obtaining clean summer fallowed fields are, therefore, 

 discussed with particular reference to their bearing on wheat aphis 

 control. 



Use of Special Tools.— It has already been said that the ordinary 

 disk harrow allows some vegetation to escape. There are now on the 

 market tools of the duck-foot cultivator type which are composed of 

 sets of overlapping V-shaped knives which will cut all vegetation just 

 below the surface of the soil. These are much more efficient than the 

 disk as destroyers of vegetation, are of light draft and do not pulverize 

 the soil as much as the disk harrow. They have the disadvantage of 

 not working well in rocky ground. 



The use of the hand hoe in destroying vegetation which has escaped 

 the first diskings is practiced by some growers, who report it a cheaper 

 and more thorough method than to continue the disking. 



Late Plowing. — In discussing the wheat aphis with many growers, 

 a surprisingly large number have remarked that fields plowed early, 

 that is, in April and May and up to June 15, were severely injured, 

 while nearby fields, plowed after June 15, were uninjured. One man 

 started plowing on May 15, but at that time plowed only an area of 

 a few rods wide around the field. On July 4, plowing was resumed 

 and carried to a finish. The following spring the early plowed area 

 was badly injured bj' the wheat aphis, while the late plowed area was 

 practically uninjured. Such cases are easily explained. On the early 

 plowed land \olunteer grain and grasses have an opportunity to start 

 up during the season of rainy weather that follows plowing, thus bring- 

 ing about inviting conditions to the migrants which are flying in June 

 and July. In late plowed fields all volunteer grains and grasses that 

 have started during the rainy season are turned under and the field is 

 left bare during the migration period. 



Some growers disk the stubble early in the spring and then do not 

 start plowing until after June 15. The disking has a tendency to 

 hasten the germination of grains and weed seed and makes plowing 

 easier. 



Some of the most successful growers plow twice, a shallow plowing 

 in early spring and a deeper plowing after June 15, well toward the 

 close of the spring rains. Such fields are remarkably free from vol- 



