1913.] PUBLIC DOCUMENT — No. 31. 173 



one in the row. If this be correct, gaps in the row would tend 

 to reduce the nnniber of plants injured below what would be 

 tlie case in full rows. 



Treatment was begun soon after the plants appeared, when 

 they were not more than an inch and a half high, and was con- 

 tinued at proper intervals until the maggots were seen to be 

 leaving the plants to pupate. At the time of the first treatment 

 no trace of maggots or of flies laying eggs could be found. Each 

 material was applied to specified rows in each plot. Between 

 these, untreated rows — usually several — were reserved as 

 checks. 



The weather during the period the tests were made was, on 

 the whole, quite favorable, there being little rain, and what there 

 was, mainly in the form of light showers. In no case did rain 

 follow an application so closely as to thereby much impair its 

 effectiveness. Occasionall}^ the wind was strong enough to cause 

 a little difficulty in applying dusting materials, but in general 

 the days were clear, warm to hot, and with little wind. 



Examination of the results of each kind of treatment was 

 made frequently, and all plants found infested were removed, 

 care being taken to remove all the maggots at the same time, that 

 they might not go to other plants and thereby increase the ap- 

 parent infestation. 



'No exact record of the number of maggots found in any sin- 

 gle plant was kept, but it was noticed that during the earlier 

 part of the season there were usually but one or two maggots 

 in each infested plant. Later, as the plants became larger, it 

 was not uncommon to find 10 or 12, or even more, in a plant. 

 Wire worms and white grubs were present, attacking the onions, 

 but in very small numbers. 



Experimental Wokk:. 

 Examination of the records of work on this insect carried on 

 elsewhere finally resulted in the selection of the following ma- 

 terials for trial: (1) carbon disulfid; (2) nicine ; (3) powdered 

 hellebore; f-l) hellebore decoction ; (5) soap wash; (6) carbolic 

 acid and lime; (7) kerosene emulsion of three different 

 strengths; (8) carbolic acid emulsion also of three different 



