548 Bulletin 78. 



follow. However, some gardeners have found that even when the crop is 

 grown on new ground, where perhaps a similar crop has never been grown, 

 that the crop is sometimes badly infested. In this case, perhaps some of the 

 flies from an old bed found their way to the new, but the more probable 

 explanation, we believe, is to be found in our discovery that the pest breeds 

 freely on at least two very common Cruciferous weeds, which would thus 

 afford a source of infection. So that a sufficient change in the location of 

 the crop is not often practicable, and will often prove unsuccessful if Crucif- 

 erous weeds abound in the new field. 



A judicious rotation of crops can not help but discourage this pest, and 

 thus gardeners may be able to grow a good crop of one or more of its food- 

 plants once in perhaps two or three years. But the market wants these crops 

 every year, and it will thus require considerable experience to know what 

 crops can be thus successfully rotated and all be made to pay well. Of course, 

 the rotating crops must be widely different botanically so as not to offer any 

 chance for the insect to continue breeding in the locality, and no Cruciferous 

 weeds must be allowed to grow in the neighborhood, for the insect could 

 breed on these until its favorite food-crop came around in the rotation. On 

 the whole, therefore, while both a sufficient change of location of the crop 

 and a judicious system of rotation of different crops each year will prove 

 quite effective in preventing the ravages of the pest, we fear that few garden- 

 ers will find either method practicable or uniformly successful. 



2. BY APPUCATIONS TO THE ROOTS BEFORE SETTING. 



This is one of the earliest methods employed in combating these maggots, 

 and is only applicable to plants of the cabbage tribe. It consists in dipping 

 the roots and base of the young plants in a puddle of some fertilizing or 

 insecticidal substance when the plant is being set. 



(a) Fertilizing Substances. 



Puddle of Earth and Cow Dung, or Night Soil. 



In her report for i88r. Miss Ormerod said: •' Dipping the plants in a 

 puddle of earth, and cow-dung, or night soil, taking care to smear the roots 

 and stems well up to the leaves with the mixture, is noted as a good preven- 

 tive." This has been quoted by several American writers. This puddle 

 would seem to offer no obstacles to the flies, in fact, it would attract them, 

 if anything, and if the pest was at all numerous it would not save the plant. 

 For its only effect would be to furnish the plant quickly available food at 

 the start which would push it along, and in this way enough roots might be 

 produced to support several maggots and the plant also. The method would 

 require considerable disagreeable labor, and we believe would have no effect 

 in lessening the number of the maggots. 



Soot, and Lime and Soot. 



In 1883, one of Miss Omerod's correspondents found that the dipping of 

 the roots in a thick puddle of soot and water was quite effective. He thought 



