352 



Kansas State Board of Agriculture. 



the fungus were brought in with seed coming from infected areas in 

 South America or Europe. 



So far as is known alfalfa and clover are the only crops affected, 

 and it is not yet certainly known whether the alfalfa crown wart will 

 affect clover. Crop rotation is the only known remedy. 



BROWN ROOT ROT OF ALFALFA (Ozonium omnivorum Shear). This 

 disease is given the common name of brown root rot in order to dis- 

 tinguish it from the violet root rot already described. It occurs in Texas 

 and neighboring states, where it has caused considerable damage to the 



cotton and alfalfa crops. The dying 

 of the plants and the spreading of 

 the disease from centers of infection 

 is very similar to the symptoms of 

 violet root rot. There is generally 

 little evidence of its presence until 

 the plant begins to wilt and dry up. 

 Cotton and alfalfa are not the only 

 hosts attacked, but the fungus lives 

 on a number of weeds. Sources of 

 infection are therefore very easily 

 carried over from one season to the 

 next. When diseased plants are ex- 

 amined carefully one will find that 

 all the smaller roots have disap- 

 peared, for they break off readily 

 when the plants are pulled. 



The fungus penetrates the root 

 tissues much as in the case of the 

 violet root rot, but it may be distin- 

 guished from the latter in that the 

 color of the fungus threads is brown 

 or brownish-yellow rather than violet. 

 Application of chemicals to the soil 

 does not seem to be effective in con- 

 trolling the disease in the regions 

 where it occurs. It is claimed, how- 

 ever, that a lack of proper soil aera- 

 tion is a prominent factor in the de- 

 i velopment of this disease. It is 



advisable to fall plow whenever possible without injury to the land, to 

 be followed by thorough disking in the spring. A two- or three-year 

 rotation is deemed necessary to insure against the source of the infection 

 being carried over. 



EEL WORM OR ROOT KNOT (Heterodera radicicola) . The nematode, 

 eelworm or root knot are various names applied to a peculiar plant mal- 

 formation produced by a microscopic worm. They live in the soil and 

 gain entrance into the young roots, where they cause swelling or "nod- 

 ules." At first sight these little knots might be mistaken for large 



FIG. 300. Root knot or eelworm at- 

 tacking tomato roots. Similar symp- 

 toms would be found on the alfalfa 

 root if infested with the eelworm. 



