June, '22 crawford & spencer: European corn borer control 233 



the very bottom of the pile. This pile being quite dry it burned com- 

 pletely to the ground. 



Ears of com that have been husked in the field should be hauled off 

 with the stalks as soon after harvest as possible so as to allow of the 

 early plowing of the field, and the waste husks should be burned. 



Since this year's com crop was so heavy (1920) several farmers in 

 .the infested districts, after filling and refilling their silos and selling 

 •what they could of the crop, biimed all the rest of it in the field. Dras- 

 tic measures, but very praiseworthy. 



The stalks of sweet com grown for factories should be cut after 

 harvest, hauled off, fed and the remains treated as outlined — or if not 

 used for feed, should be cut in the field with a mower, raked into win- 

 drows and, when thoroughly dry, biuned. Some factories sell their 

 corn stalks and cobs that were grown on contract ; some ensile it as well 

 as the cobs after being shelled at the factory, and sell the ensilage. 

 This whole practice is to be recommended, since they may harbor 

 larvae. Com cobs after being shelled, should be burned (if not used as 

 fuel) in the waste pile, rather than be left lying around the yard. 



Second Phase. "The destruction of larvae remaining in stubble 

 and crop refuse in the field after the crop has been removed." 



Stubble in any position and debris on the surface and weeds growing 

 among com, can and do harbor larvae. 



In stubble we have found as high as 11000 to 14360 larvae per acre. 



In debris we have found as high as 31000 larvae per acre. 



In weeds we have found as high as 24000 larvae per acre. 



Stubble left standing in the field or plowed out and left lying on the 

 surface, constitutes almost ideal sheltering conditions for over winter- 

 ing larvae. It has been found impracticable to dig or plow out stub- 

 ble in order to pile and bum it. 



Under conditions that existed in Ontario 1920 and in the fall of 1921, 

 "we have found that the plowing under to a depth of 6 inches, of stubble 

 and debris, as early as possible after the removal of the crop is the factor 

 of control second only in importance to the silo. About the middle of 

 September is the latest safe date for plowing to work, at Port Stanley, 

 Ont. if the larvae are to be forced to leave the stubble in largest possible 

 numbers. 



The efficiency of plowing is in direct ratio to its earliness. By the 

 end of October, the upward migration has ceased to be of much conse- 

 quence and larvae in stubble and debris, plowed under at and after 

 that date, will remain underground through the winter without suffering 

 heavy mortality and migrate out before the last of April the following 

 spring. 



