136 IOWA ACADEMY OF SCIENCE Vol.. XXVI, 1919 



During the summer referred to, hopper-dozers similar in con- 

 struction to the model recommended by the U. S. Department of 

 Agriculture were made and used with excellent results in many of 

 the infested areas: Lee county, through the aggressive efforts of the 

 county agent, Mr. J. S. Clare, probably did more with the hopper- 

 dozer than was done in any other county of the state. More than 

 twenty machines were made and successfully operated in that 

 county. 



The case of Mr. Otto Krebill, living west of Donnellson, will il- 

 lustrate the success of this work. Early in June, having just finished 

 cutting his first crop of clover, he found many young grass-hoppers 

 appearing in the meadow. A hopper-dozer of the type already re- 

 ferred to was built and put into operation. Not wishing to go to 

 the expense of metal pans, matched flooring was used and a lining 

 of tarred building paper applied. This, however, did not prove to 

 be the success that had been anticipated, as the kerosene soon 

 reacted on the building paper. A pan carefully constructed of good 

 lumber may be made sufficiently water tight. 



Another improvement was made, however, which proved to be of 

 considerable value and was copied by many makers of hopper-dozers 

 throughout the state. Mr. Krebill observed that the junior mem- 



Fig. 33. — Krebill's meadow. 



hers of the tribe, on many occasions could not leap the nine inches in 

 height necessary to get over the front of the pan. Accordingly, a 

 twelve-inch board was placed in a diagonal position with one edge 



