280 



The Control of Maggots. 



[June, 



THE CONTROL OF MAGGOTS 

 ATTACKING THE ROOTS OF 

 VEGETABLES. 



Kenneth M. Smith, A.K.C.S., 

 Adviser in Agricultural Entomology , Manchester University. 



Insect pests of vegetables have been very much ne^lectad by 

 research workers in this country, especially insects attacking 

 onions and carrots, and to a less extent those injuring cabbages 

 and turnips. 



Cabbage Root Fly. — In America, where pests of vegetables 

 receive much more attention, efforts have been made to devise 

 a satisfactory means of control for the maggots of Chortophila 

 brassicae, the cabbage root fly, which attack the roots of cab- 

 bages, cauliflowers, turnips, etc. 



One of the methods of control recommended is the device 

 known as the tarred felt " disc," which consists of a small square 

 of ordinary tarred roofing felt which is slit in the manner shown 

 in the diagram.* These squares are placed round the stem of 

 the plant at the time of planting out in the field and act mechani- 

 cally in preventing the fly from laying her eggs on the plant. 

 To place the square in position, the main slit is opened and the 

 two flaps in the centre are lifted up ; it can then be slipped 

 round the stem and pressed down close around it. The squares 

 must lie flat on the soil to be correctly applied, and the soil 

 should be in a friable condition to enable them to do so. They 

 should be about 1\ in. square and can be cut from a sheet of 

 tarred felt with a sharp knife. It is important that the material 

 used should be tarred roofing felt and not the thin paper some- 

 times sold as felt. 



As regards preventive measures for this fly by means of 

 chemicals, good results have been obtained by using ordinary 

 creosote applied to the plants, mixed with some substance like 

 dry soil or precipitated chalk to act as a " carrier or 

 " spreader " of the creosote. It is inadvisable to use sand as 

 the spreader because it does not absorb the chemical. The pro- 

 portions should be two parts by weight of creosote to ninety-eight 

 parts of chalk or earth. If possible precipitated chalk should be 

 used as the spreader, as it takes up the chemical readily, is 

 easily applied, and is cheap. In order to obtain the correct 

 proportions of the mixture it is better to weigh out the respective 



* See also this Journal April, 1918, p. 59. 



