44 



PROTECTION OF PLANTS, 1921-22 



When the sodium arsenite mixture was apphed as a spra}', an ordinary 

 watering can with a small nose was used. Acre plots were treated quickly when 

 the operator began at one end of the plot and walked diagonally across the crop 

 back and forward in a V-shaped manner, the strips being about 15 or 20 feet 

 apart at the wide end. 



The first application was made when the plants were three or four inches 

 high, and four or five further applications made about a week apart. Bright 

 calm days should be chosen for such work. 



Life-history of the Onion Maggot Fly. — The adult flies, which are about 3^ 

 inch long and bristly, begin to appear about the middle of Maj", and about 

 ten days afterwards the females hegi?} to lay their eggs on the leaves. These are 

 cylindrical, white and distinctly ridged. The eggs hatch in three to five days, 

 and the maggots are white, cylindrical and less than half an inch long when full 

 grown in 2 to 5 weeks. Thej^ work their way down within the sheath of the 

 leaves to the forming bulbs in which they feed. 



When the maggots are full grown they form oval, brown puparia, either in 

 the outer layers of the bulb or in the soil, about 2 to 5 inches below the surface. 

 In about two weeks flies emerge from the puparia. There are probably three 

 broods a year, and they pass the winter as puparia in the soil. 



The control method is based on the fact that the flies do not lay their eggs 

 until about ten days after emergence from the ground, and that they are fond of 

 sweet substances. 



Following are the resuHs aiKl summaries of the experiments: — 



MONTREAL ONION MAGGOT CONTROL WORK, MONTREAL. 



