Ch. XVIII.] ON TURNIPS. 243 



most usual mode of destroying these worms is by heavy rolling during the 

 night, as it is then they come out to feed ; but it is very far from being 

 efl'ectual in rough and stony soils. Ducks may, however, be successfully 

 employed for the purpose of devouring them, and so certain is this expe- 

 dient, when the flock is sufficiently large, that a field of thirty-three acres 

 was effectually cleared witliin five days by 400, which were turned upon the 

 farm of Mr. Coke at Holkham *. Much injury has been latterly expe- 

 rienced from an attack of mildew on all the varieties of turnip, when half- 

 grown, but the Swedish and yellow turnips have suffered most frequently 

 and severely from it. 



The most destructive enemy which the crops have to encounter is, how- 

 ever, a small winged insect, well known to all farmers under the common 

 name of the " turnip-fly." It makes its appearance as soon as the tender 

 seed-leaves of the plant burst forth, and frequently swarms in such numbers 

 as to completely strip them, but disappears the moment the growth of the 

 root converts the buds into rough-leaf. This usually happens within a few 

 days after the seed-leaves have first sprouted, and within that short space 

 of time it commits such serious mischief as sometimes to require the ground 

 to be resown. 



Numberless expedients besides rolling have been resorted to, with a 

 view to check this evil, among which top-dressings of soot and quicklime 

 have been the most strongly recommended ; and, from some experiments 

 made by the Earl of Thanet, and published in Mr. Greg's account of his 

 farm in Hertfordshire, on the application of the latter, great expectations 

 were formed of its success. The mode of applying it is in powder strewed 

 along the drills and dusted over the leaves the moment the turnips come 

 up, the quantity employed being usually six or eight busliels per acre ; but 

 a much larger amount may be used without injury to the plants, and may 

 be considered useful as affording a dressing to the land. It should, how- 

 ever, be laid on when the weather is quite dry, as a shower of rain will 

 slake it. Its effects have accordingly been extensively tried, and in many 

 instances found useful ; but the accounts are so contradictory that the 

 advantages which have been found to result may be not unreasonably 

 ascribed to some favourable circumstances in the weather ; and we have 

 lately learned from the nejAew of Mr. Greg, that the plan was, on his 

 farm, found ineffectual. 



Sir Humphry Davy records an experiment made with a composition 

 consisting of three parts of soot and one part of quicklime, slaked with 

 urine, about four bushels of which, per acre, were let to f;dl into ihe drills 

 along with the turnip-seeds ; the result of vvhich was, that the rows to which 

 the compost was applied were scarcely touched by the fly, while those 

 adjoining to them were eaten awayt- Oii this, however, it maybe ob- 

 served, that although the volatile alkali of these mixtures may be off'ensive 

 to the insects, yet they also afford a highly stimulating food to the plant, 

 which may thus be put speedily out of danger ; for the most weak and 

 sickly sprouts are always the first to be attacked. The sowing of radish 

 seed intermixed with turnips has also been successfully tried as a preventive 

 of the fly|. The burning of weeds and damp straw have also been found 



* Complete Grazier, 6th edit. p. 517. 



f Lectures on Apfricultural Chemistry, 4to. p. 320. 



J The Ceres gold medal of the London Society of Arts has also been awarded to Mr. 

 Poppy, for an experiment made on his own farm, in which four acres were sown in drills 

 with the usual quantity of Swedes intended to stand for a crop, and half a peck per acre 

 of common turnips in alternate rows for the purpose of attracting the fly. The result 



r2 



