80 THE REPORT OF THE No. 33 



In 1923, conditions within the control area (34 fields), with an average stalk 

 infestation of 36.48 per cent., indicated an increase in intensity of about 10 per 

 cent, in the stalks and a somewhat higher increase in percentage of injury to 

 plant structures such as cobs and shanks over the 1922 conditions. This increase 

 was generally distributed throughout the whole control area. Even this increase 

 was still 22 per cent, less than the 1921 average. None of the sweet corn of 1923 

 was ruined, the highest losses in the most severely infested fields not exceeding 

 50 per cent. 



As was the case in 1922, the infestation in the control area was distinctly 

 less intense than that in the surrounding areas. The most severely infested 

 fields in the district were all outside the control zone. This is in marked contrast 

 with the former distribution of intensity, when the focus for most intense infesta- 

 tion and loss was within this area, as in 1920 and 1921. 



No definite figure has been developed to indicate exactly the actual loss in 

 any year. However, an idea of the relative annual losses and severity of attack 

 can be secured if we assume as an estimate that the loss as a farm crop in the 

 control area was about 15 per cent, in 1921, that in 1922 would be about 2 per 

 cent., and that in 1923 not over 4 per cent. 



The general trend of infestation in the surrounding district has been in 

 marked contrast to the situation within the control area. To the west for six 

 or seven miles the infestation increased very abruptly during the years 1921 

 and 1922 when very severe losses were suffered. The intensity, however, in 

 1923 in this region decreased quite markedly from this high point. Just why 

 is not known. To the north the infestation has increased steadily, but not 

 nearly as abruptly as in other directions, throughout the period from 1920 to 

 1923. To the northeast and east the trend of the infestation has been steadily 

 upward, both in percentage infestation and in total population of larvae. At 

 the present time, November, 1923, the focus of highest infestation and loss has 

 shifted to the north and east and comprises a more or less oval area beginning 

 at the northeast corner of the control area and extending for about 20 miles in 

 a general northeasterly direction. The increase in infestation in this area was 

 most conspicuous in 1923, both in flint corn and in canning sweet corn. 



Very little mention has been made of the narrow strip of country to the 

 south of the control area. It consists of a zone one mile wide, which does not 

 comprise many corn growers, lying between the control area and the lake shore. 

 These growers in the cases where they have instituted the practice of late 

 planting have been experiencing a clear decrease of infestation, though in other 

 cases they have suffered very severe losses. In general the trend is downward, 

 both on account of the control practice and also doubtless on account of the 

 protection afforded by the destruction of larvae in the control area to the north. 



The control suggestions made to the farmers in the observation area by the 

 personal canvass were reinforced by the increasing losses being suffered and 

 resulted in a noteworthy change in certain phases of handling the corn crop in 

 the area. In 1922, the last year of normal planting, 55.5 per cent, of the corn 

 crop was of the flint type, the most susceptible type to European corn borer 

 infestation and damage. Of this part of the local crop 45 per cent, was planted 

 by the 24th of May, 78 per cent, by the 1st of June and 85 per cent, by July 6th. 

 Of the dent corn of this year 10 per cent, only was planted by May 24th, 85 

 per cent, by June 1st and 90 per cent, by June 6th. 



