lO 



once made for studying them with a view of finding the best way to 

 cope with the evil. Mr. A. W. Rymer Roberts undertook this work. 

 The attack was not so serious as was feared ; it was, however, sufficient 

 to show the urgent need for the work. 



Two lines of investigation were followed. The natural way of life 

 of the wireworm in the soil was studied in order to obtain full information 

 as to its habits and its weaknesses ; and search was made for some 

 insecticide or method of treatment that would prove fatal to the 

 wireworm. The last problem speedily became linked up with another 

 that has been under investigation for some time and had proved rather 

 baffling — the search for a practicable sterilising agent. As s'hown in 

 previous reports, if soil is treated with a volatile antiseptic there is a 

 considerable gain in available nitrogen compounds and therefore 

 an increase in productiveness. Toluene and carbon disulphide 

 were very effective in pot experiments but not in the field ; some of the 

 tar acids, notably cresylic acid (the chief constituent of the so-called 

 " liquid carbolic acid " ), proved to be m )ro suitable on the large scale. 

 Investigation has shown that carbon disulphide, in quantities practic- 

 able on the farm, is of no great insecti :id J Vc.lue. In the pot experi- 

 ments this did not matter, as insects and eelworms were rigidly excluded, 

 being outside the scope of the investigation.; in the field, however, 

 they were important factors. The broad resvlt of the efforts to put 

 soil sterilisation methods into praciice is that the process is effective 

 but not economical in comparison wil h cheap sulphate of ammonia or 

 nitrate of soda. The situaiion would be comjJctely altered, however, 

 if a partial sterilisation agent could be found that is at the same time a 

 soil insecticide ; we should then obviou;;.ly have a much better prospect 

 of success in field work than we have had in the past, when we confined 

 ourselves to the gain in available nitrogen only. Mr. Tattersfield is, 

 therefore, preparing a series of suitable subst.mces in the Chemical 

 laboratory ; Mr. Roberts is testing their larvicidal effect on wireworms 

 and other pests ; and through the generosity of Mr. W. B. Randall it 

 has become possible for aaother wjrker, Mrs. D. J. Matthews, to 

 study their effects on the br^.c^erial and protozoan population. Two 

 groups of substances are being tested : (a) compounds of known 

 constitution, so as to see what chemical groupings are most effective, 

 knowing which it may be possible to formulate specifications for sub- 

 mission to a Works chemist, and (b) certain typical waste products 

 now available in quantity at a cheap rate. 



The resistance of the wireworm to certain poisons such as carbon 

 disulphide, toluene and formaldehyde, which ought to be effective 

 but are not, is of considerable interest. Dr. Malcolm Laurie is 

 studying the morphology of the wireworm in the hope of gaining 

 information that will be of service. 



The most potent soil steriliser and larvicide is heat ; further attempts 

 have therefore been made to devise means of heating soil cheaply on a 

 large scale. In the form first worked out at Rothamsted the method 

 cost 5/- per ton of soil, or about £300 per acre of land, a hopelessly 

 impractical proposition for the farmer. But the nurserymen in the 

 Lea Valley succeeded in bringing down the cost to below £40 an 

 acre at pre-War prices. This figure is not e.itirely out of the question 

 for special types of crop production, such as market gardening and 

 nursery work ; if the cost could be further reduced to one third or one 

 quarter, the method would be quite practicable for potato growing, etc. 



