J. T. Wadsworth 89 



Precautions to be observed in applying the discs, and 



OTHER remarks. 



In order to obtain the best results from the use of tarred felt discs 

 it is advisable that the soil should be in a fine friable condition when 

 the discs are placed in position, and further, that the plants should not 

 be placed in depressions of the soil but if possible on a slight ridge. 

 If the soil is lumpy the discs will not lie fiat on the ground and the 

 female flies will then be able to crawl underneath the discs to deposit 

 eggs. If the discs are placed below the soil level they are liable to 

 become covered with soil after rains, which renders them less efficient. 

 It is also of the utmost importance to place the discs round the plants 

 immediately after planting out, if this operation is performed later 

 than the first week of May. In the district around Manchester, eggs 

 of the cabbage-fly were found on May 14th in 1915, and on May 18th 

 in 1916 ; these were the earliest dates they were found in those seasons. 

 Probably in the South of England they would be found much earlier, 

 and in the North somewhat later. On seedlings planted out earlier in 

 the year, it is not so important to place the discs in position immediately 

 after planting, although there may be advantages to be gained by 

 doing so. 



Several of the observers, who have tested the tarred felt discs, draw 

 attention to the fact that protected plants are usually larger, and mature 

 earlier, than unprotected ones. These differences are rightly attributed 

 to freedom from root injury owing to the absence of maggots on the 

 roots. Another possible factor, which contributes to this result of 

 increased size and early maturity, may be referred to here. If the soil 

 underneath the discs is examined on hot days, during the first two or 

 three weeks which follow the planting out of the seedlings, it will be 

 found in a moist condition, whereas the soil round the unprotected 

 plants will be dry. The disc, by preventing evaporation from the surface 

 of the soil, conserves the moisture in the soil directly beneath it. The 

 plants are thus enabled to recover more quickly from the effects of 

 transplanting, and the conserved moisture also helps them to withstand 

 better the effects of prolonged drought. More especially is this the 

 case with regard to cauliflowers, which suft'er more from drought than 

 cabbages. 



The question is frequently asked whether the discs, owing to the 

 smell of the creasote with which they are impregnated, deter flies from 



