February, ’24] 
CRAWFORD: PLOWING FOR CORN BORER 
133 
vestigations in ploughing as a factor in control have been published 5 , 6 , 7 , 
but they differ so considerably from published general statements of 
United States workers, such as Vinal 1 , 2 , Felt, 3 and Caffrey, 4 that it has 
seemed well to present a somewhat detailed review of the Canadian 
work. The results at least show in strong relief the extreme dissimi¬ 
larity in the habits of the larvae in different geographic regions and the 
impossibility of making blanket control recommendations. 
The disposal of the entire crop refuse in the field by gathering and 
burning was demonstrated to be prohibitive in cost as a practical farm 
measure even under the most favorable circumstances. Hence the 
effect upon the larvae and the value in control of the ordinary farm 
ploughing was studied intensively both by means of burial experiments 
with infested stalks made by hand at definite depths and by turning 
down ordinary crop refuse with the single furrow walking plough. As 
the larvae used were always in their natural position in the infested 
stalks the exact number of larvae present was never definitely known. 
An approximate idea was secured and expressed as a general minimum 
expectation, by counts made in stalks of a similarly injured appearance, 
from which the average number of larvae per stalks was determined. 
Nicely graduated, exactly comparable, numerical results were not 
secured, though the general trend and the gross results were clear. 
In the burial studies the numbers of larvae recovered in the material 
below ground for various periods were recorded. In the ploughing 
experiments the larvae were taken in traps into which they crawled 
naturally after coming to the surface and where they were easily 
recovered and recorded each day. 
Mortality Below Ground 
Throughout the investigation mortality below ground, in important 
proportions, has always been conspicuously absent except in one series 
of experiments, in which large quantities of stubble were used in layers 
a foot thick and covered by 12 or more inches of soil. The only other 
case where significant mortality occurred was in an overwintering burial 
experiment in ground across which the natural drainage of the field 
took place throughout the fall, winter and spring. 
No clear increment of death rate throughout the fall, winter or spring 
due to the larvae being below ground has been observed in experiments 
with loose bundles of ten stalks, either in burials down to 24 inches or 
in series of the same type of experiments at the uniform depth of 6 
inches. The same was true of the larvae in material ploughed down 
