PARASITIC PLANTS 267 



vention of seeding is doubly important, because not 

 only are large quantities of seeds produced, and easily 

 scattered by the wind, but they may lie in the soil for 

 years without losing their vitality. It has been recorded 

 by Frank that in one case the pest again attacked 

 clover which was sown seven years after the previous 

 crop. The later crop was so severely infested that it 

 had to be ploughed up. On infested land, therefore, 

 clover crops should be as widely separated in the rota- 

 tion as possible. 



3. The growth of heavy-yielding varieties of red 

 clover is believed to be valuable on account of the 

 strong, luxuriant, and rapid growth, well covering the 

 soil. It is, indeed, known that in Switzerland home- 

 grown, heavy-yielding red clover is hardly attacked, 

 while foreign, less robust kinds suffer severely from 

 Broom-rape attack. Red clover may also be replaced 

 by lucerne or sainfoin. 



4. The Swiss Leaflet recommends the sowing of 

 Italian ryegrass with the clover, the reason being that 

 it grows rapidly after the first cut is taken, and prevents 

 the continuous warming of the soil and keeps the 

 Broom-rape back. On land on which clover has pre- 

 viously suffered from Broom-rape pure red clover seed 

 is therefore not sown, but is mixed with a fair percentage 

 of Italian ryegrass, not more than about 5 Ib. per acre. 



5. It is recommended by Frank that badly infested 

 fields should be deeply broken up after the first cut of 

 clover is taken, and before the pest blooms. The land 

 should then be used for other crops for some years. 

 Somewhat similar advice is given by Percival, who says 

 that, " When once established it is difficult to eradicate 

 before doing considerable injury to the crop, and 

 nothing short of ploughing up the clover will exter- 

 minate the pest entirely." 



