9(1 Report on a Trial of Tarred Felt "Discs'' 



laying eggs. Whilst the creasote may exercise a deterrent influence 

 on the flies for a short period of time after the discs have been placed 

 round the plants, this influence— supposing it to exist — soon disappears. 

 Frequently eggs may be found both on the surface of the discs, and also 

 underneath them : a fact which tends to disprove the idea that flies are 

 deterred from laying eggs owing to the emanation of odours from the 

 discs themselves. The chief function of the disc is to act as a mechanical 

 obstacle to the efforts of the flies to deposit eggs in the soil near the 

 plant. 



Growers have also asked for information regarding the action of the 

 discs on slugs. No definite experiments have been made with the 

 object of determining the effects of the discs with regard to slugs. It is 

 worthy of note however that, in the row of 233 cauliflowers adjoining 

 the field of clover (see Fig. 1), only two plants were definitely proved 

 to have been injured by slugs. As numerous slugs were observed in wet 

 weather along the edge of this field, it would appear probable that they 

 do avoid the discs. Occasionally a slug was found sheltering beneath 

 a disc, but this was where the ground was lumpy and spaces were present 

 underneath the disc. If the discs are pressed closely to the soil, no 

 accommodation would remain for slugs, and they would thus be pre- 

 vented from crawling underneath. 



Several market-gardens were visited during the summer months in 

 order to determine the relative proportion of plants destroyed by maggot 

 attacks on different types of soil. An interesting fact was observed in 

 a market-garden situated about two miles from the one where the above 

 described experiments were conducted. Although I examined hundreds 

 of cauliflowers there, it was difficult to find a single plant infected with 

 root-maggots. The soil is a heavy clay loam — the owner described it 

 as a good strong soil — and the gardener attributed to this fact his 

 immunity from root-maggot attacks. He also uses gas lime abundantly, 

 having a strong belief in the beneficial effects of this substance against 

 root-maggots and pests generally. The contrast between the two 

 cauliflower plots, at the end of July and early August, was very striking. 

 On the one plot, where the soil was light in character, from fifty to sixty 

 per cent, of the cauliflowers were destroyed by maggots : on the heavy 

 soil, hardly a single plant, in three or four hundred, was lost from this 

 cause. All the growers, with whom I discussed the matter, agreed that 

 cauliflowers and cabbages are more liable to become infested with root- 

 maggots when grown on light soils, than they are when grown on heavy 

 soils. Various reasons were given in support of this opinion, and 



