36 WEEDS OF FARM LAND 



at the next stage in cultivation. Fresh seedlings arise to 

 meet with the same fate, and very few plants are able to 

 reach maturity to replenish the store of seed in the soil. Two 

 root crops in succession will make a wonderful clearance even 

 on badly infested land, and this method has been successfully 

 used in getting rid of shepherd's needle (Scandix pecten\ which 

 is troublesome in some places. 1 



A totally different method is adopted when " smother 

 crops " are grown. In this case the weed and crop seeds 

 start into growth together, but before long the crop grows 

 ahead much more rapidly than the weeds, and as the latter 

 are deprived of light by the overshadowing of their competitors 

 they are killed out before they attain any size. Clover, 

 lucerne, sainfoin, and mustard are among the more common 

 smother crops. Lucerne is particularly effective, because it 

 is cut so often during the season that all the weeds that grow 

 are cut off before they seed, and as the crop occupies the 

 ground for several years a good clearance is effected. Couch- 

 grass {Agropyron repens] has beeli effectively dealt with in this 

 way. In a French test 2 vetches were sown on a field infested 

 with couch-grass in April, 1910, and a good hay crop was 

 taken in July. By this time the vetches had " gone down " and 

 smothered all the top growth of weeds, so that after mowing 

 the field was clean and fit for sowing lucerne the following 

 spring. Three good cuts of lucerne were obtained in 191 1, as 

 the couch had no opportunity of asserting itself and spoiling 

 the crop. 



When crops are grown for silage very good opportunities 

 arise for clearing the land of weeds, provided the ground is 

 broken up directly the crop is removed, so that the weeds are 

 foiled in any attempt to reassert themselves. 3 The silage crop 

 exhausts the soil moisture very considerably, and if the ground 

 is ploughed without delay the weeds rapidly dry up, particu- 

 larly if the piocess is favoured by hot, dry, summer weather. 

 It is usually possible to carry out this work because it comes 

 between hay and corn harvest, when more time is available. 

 The perennial weeds are not exterminated by such silage crops 

 as oats and tares, but they are suppressed for a time and so 

 weakened that they are more easily dealt with in other ways. 



1 Long, H. C. (1912), " Identification and Eradication of Some Common 

 Weeds, IV," Jour. Bd. Agric., XIX, pp. 273-277. 



2 La Terre Vaudoise (1911), No. 50, p. 458. 



3 Amos, A. (1917), "Some Problems in the Growth of Silage Crops," 

 Jour. Bd. Agric., XXIV, pp. 167-168. 



