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BULLET IX 1266, U. S. DEPARTMENT OF AGRICULTURE. 



Control. — The only satisfactory way of controlling root-knot is 

 by crop rotation, using crops not attacked by the nematodes between 

 the tobacco crops. Cropping with corn, wheat, oats. rye. peanuts, 

 sorghum, velvetbeans, or Iron or Brabham cowpeas for three years 

 usually suffices to rid the land of nematodes if weeds acting as host 

 plants are kept down to a reasonable extent. Precautions should 

 be taken, of course, to prevent seed-bed infection through the soil 



as a harboring agent. 



BROOM RAPE. 



Description. — Broom rape is a fairly large flowering plant, devoid 

 of leaves or green coloring matter (chlorophyll), which is capable 

 of parasitic growth upon tobacco and other plants. Lacking 

 chlorophyll, it is wholly incapable of manufacturing plant tissues 



Fig. 16. — Earlier stages of development of broom rape on tobacco. This para- 

 sitic plant attaches itself to the roots of tobacco, feeding upon them and con- • 

 sequently producing damage in case of heavy infestation. 



from the elements of the soil, water, and air and can exist only by 

 attachment to certain other green plants from which it draws its 

 nourishment, much like fungi and bacteria. It therefore resembles 

 in its behavior in many respects the well-known dodders. The 

 broom-rape seeds germinate in the soil, and the young plants attach 

 themselves to the roots of the tobacco plants and grow to a size as 

 large as 18 inches in length, often in very thick clumps of white, 

 yellow, brown, or purplish stems arising i'rom the ground to some 

 height at the base of infected plants (figs. 16 and IT). These stems 

 produce flowers and seeds, the latter being very small, but once in 

 the soil they are capable of remaining dormant for long periods, 

 subsequently germinating and attacking susceptible crop plants. 



Just how much damage broom rape may do to tobacco in lowered 

 yield and production is not fully understood. In many cases heavy 

 infection with broom rape apparently has not done much harm. In 

 other cases, however, stunting of infected plants is apparently 



