February, ’24] 
CRAWFORD: PLOWING FOR CORN BORER 
137 
pared with the average for the field. The number of larvae were checked 
against the number recovered on the inside of the trap to determine the 
percentage of larvae coming to the surface both in spring and fall. 
The results of these experiments were uniform almost to the point of 
monotony and bore out to a remarkable degree the results foreshadow¬ 
ed by the hand burials, that is; the larvae left the stalks and stubble 
underground and came to the surface. 
Tabulations Nos. 1 and. 2 give representative results of these experi¬ 
ments, illustrating some of the points of interest. The results in tabu¬ 
lation No. 2 are given in seven day totals of daily recoveries by weeks 
after the experiments began. 
The first ploughing of the season was on August 7th, 1921. It con¬ 
sisted of a strip of standing sweet corn ploughed under, of which one half 
was rolled and carried little refuse on the surface. Eleven days after 
ploughing 2 hills were taken up and but 29 larvae were recovered where 
114 were expected (See Tabulation No. 1, Section 1). By the 23rd of 
September, 3 hills yielded but 3 larvae where at least 171 were expected 
and by November 1st no larvae were to be secured below ground and 
none were found the following spring. Some of the larvae which thus 
came up found their way into the slight refuse on the surface, ten feet 
of which yielded as many as 45 larvae and two corn husks 11 larvae. 
The rest of the larvae simply disappeared. 
The early fall experiment involved normal com refuse in a very severely 
infested field with an estimated population in the refuse of 31,000 larvae 
per acre. The greater part of this field was ploughed September 19-23, 
and immediately seeded to wheat. Counts in the material ploughed 
down showed that the population below ground dropped to .05 larvae 
per stubble and .2 larvae per foot of stalks, while the refuse on the surface 
rose in larval content to 1.75 larvae per stubble and 3.5 per foot of stalk. 
Only a small proportion of the larvae actually found their way into the 
refuse as the surface was remarkably clean. The greater proportion 
of the larvae simply disappeared and could not be demonstrated either 
in the soil, the corn refuse in the unploughed part of the field or in the 
grass on the headland. 
Seven serial fall ploughings were carried out in 1922 (See Tabulation 
2, Section 1) and were in normal refuse with an estimated larval popu¬ 
lation of 33,800 larvae per acre. The experiments began on September 
28, 1922 and ploughings continued at intervals of a week until Novem¬ 
ber 9th. The larvae emerging from below ground were recovered and 
taken from the traps daily. They began to come to the surface the 
