SOIL MANAGEMENT. 61 



Witch weed or Rooibloem (Striga lutea). — As the seeds 

 germinate only when close to or in contact with grass plants, 

 and may germinate year after year for a considerable period, 

 it is an extremely difficult weed to exterminate. In very badly 

 infested fields often the best course is to change permanently 

 the class of crop, avoiding grasses. Peanuts, potatoes, lucerne, 

 cowpeas, pumpkins, and so on, may be erown instead. If 

 the infestation is not very marked, germination of the seed 

 may be stimulated by growing a crop like teff or Sudan grass 

 thickly. A hay crop is then harvested before the weed flowers, 

 and the field ploughed before the seed stage is reached. This 

 practice should be repeated, and the class of crop changed for 

 one or two seasons. 



Khaki Bos {Tag etas minuta). — This weed has become 

 notorious. Although it seeds heavily it can be readily con- 

 trolled by frequent harrowings when in the seedling stage, and 

 before crops are planted. If necessary, planting should be de- 

 layed for a few weeks in order to allow extra harrowings. 

 Plants which have found a footing along: fences or ditches 

 should be destroyed by hand before they produce seeds. 



Kweek iCynodon dactylon). — In areas of summer rainfall 

 plough during the latter part of summer or later, if the soil 

 permits, leaving the furrow slice standing on its edge. Before 

 the early rains commence, cross plough and harrow. As pre- 

 viously stated, in winter rainfall areas the operation must be 

 commenced by ploughing during the early summer months. 

 Lucerne lands are often so badly infested with this weed that 

 the stand becomes very sparse and consequently the crop must 

 be ploughed down. The growth of kweek in lucerne can, how- 

 ever, be checked to some extent by watering the crop once in 

 winter and then harrowing with a heavy type of lucerne culti- 

 vator. Poorly screened lucerne seed often introduces kweek 

 seed into fields which are unlikely to become infested from 

 other sources. Every care, then, should be taken to buy pure 

 seed. 



