PREVENTION AND ERADICATION OF WEEDS ' 51 



Some weeds, however, seem to be proof against all 

 methods of eradication, especially if they occur on soil to 

 which they are particularly suited and where they normally 

 grow in great abundance. Corn marigold (Chrysanthemum 

 segetum) tends to resist all attempts to remove it. In one 

 case, 1 when it had so completely destroyed two acres of 

 barley that harvesting was not attempted, the land was 

 sown down to green crops for four successive years with no 

 success. This weed has long had an unenviable reputation, 

 for even in 1727 Threkeld wrote, " Maunour courts do amerce 

 careless tenants who do not weed it out before it comes to 

 seed ". Some success may be obtained by growing several 

 successive root crops on infested land, provided scrupulous 

 care is taken with the hoeing so as to allow no plant to seed. 

 Older writers claim that manuring with chalk is effective. 2 

 This weed is very troublesome in turnip fields on the sandy 

 soil of Norfolk. 



Wild oats is a bad weed in some districts and is difficult 

 to get rid of. Adam 3 (1789) claimed that it could be 

 eradicated by putting infested land down to clover and mow- 

 ing the oats and clover together before the oats were ripe. 

 The plant is annual, so the roots do not shoot out again, and 

 flowering would thus be prevented. It seems doubtful 

 whether one year only of this treatment would be really effec- 

 tive. Observations made by the writer in Suffolk seem to show 

 that wild oat seed is capable of lying dormant for some years, 

 and a stock of ungerminated seed would probably remain 

 ready to spring up after the removal of the clover crop. Deep 

 ploughing of land infested with wild oat serves to bring up a 

 large stock of dormant seeds into conditions favourable for 

 germination. Some of these germinate at once and are 

 cleared away if thorough surface cultivation is carried out. 

 Most of the seeds, however, bide their time and germinate 

 among succeeding cereal crops, so that the deep ploughing 

 really encourages an increase in the crop of wild oats in future 

 years ; in France it was considered that the deep plough- 

 ing carried out in 1912 favoured the invasion of this pestilent 

 weed in 1913.* 



When a smother crop is grown it is of course necessary 



*Jour. Bd. Agric. (1907), XIV, pp. 536-537- 

 1 " Gleanings from Agriculture" (1802). 



3 Adam, J. (1789), " Practical Essays on Agriculture," II, pp. 173-198. 



4 Rabate", E., "La Folle Avoine" (1913), Le Progres Agricole e Viticole, 

 33, No. 32, pp. 116-180. 



4 * 



