PREVENTION AND ERADICATION OF WEEDS 63 



an untreated plot, flowering and fruiting abundantly. Possibly 

 a heavier dressing might have had more permanent effect. 1 



II. Eradication of Weeds from Grass-land. 



On arable land certain periods constantly recur when the 

 land is free from any crop, and even when a crop is growing 

 there are spaces of bare soil between the plants which permit 

 of cultivation. On grass-land all is different. The crop is 

 always on the ground, and the plants are so closely associated 

 that they are interlaced, and roots and shoots alike help to 

 form a mat which completely covers the surface of the ground. 

 For this reason weeds on grass-land can never be dealt with 

 without taking the crop into full consideration, and the methods 

 of eradication differ considerably from those adopted on arable 

 land. They may, however, be subdivided into the same two 

 main divisions of "mechanical " and "chemical " means. 



(a) Eradication by Methods of Cultivation Mechanical 

 Means. When grass-land is constantly grazed or constantly 

 cut for hay the herbage takes on a special character according 

 to the method of treatment, and certain weeds find congenial 

 circumstances under each set of conditions. It is possible to 

 take advantage of this in the eradication of the weeds, as by 

 reversing the usual order and haying a grazed pasture, or 

 grazing a mown field, the conditions are altered and the weeds 

 do not flourish so well. Oxeye daisy (Chrysanthemum leucan- 

 themum) grows very strongly in hay fields but resents inter- 

 ference in the early stages of growth. Close grazing 

 with sheep in the early spring will materially reduce it, and 

 for the same reason very early cutting of the hay crop is 

 effective. This method can also be used to reduce false brome 

 (Brachypodium sylvaticum and B. pinnatum] where it is plenti- 

 ful, as on down pasture. Care is needed when animals are 

 used as weed eradicators, as if the grazing is carried out on 

 the wrong lines the weeds may be increased rather than 

 diminished. A field known to the writer at Carhampton 

 (Somerset) was infested with hardhead (Centaurea nigra}. 

 When the land was grazed exclusively by cows the hardheads 

 waxed more and more strong, the cows apparently leaving 

 them severely alone, but when sheep were run in as well 

 an improvement was soon noticed, as the plants were grazed 



1 " Experiment to Check the Growth of Spurry," Jour. Bd. Agric. (1901), 

 VIII, p. 54- 



