B. P. I.-667. 



ROOT-KNOT AND ITS CONTROL 



INTRODUCTION. 



The disease of plants known as root-knot, beaded root-knot, root- 

 gall, eelworm disease, big-root, and probably under other names has 

 been present in the United States for many years and has caused 

 losses whose extent can not be calculated. Although more abundant 

 in the South, it is present, at least sporadically, in all but the most 

 Northern or Northwestern States as an out-of-doors pest and is every- 

 where distributed in greenhouses. 



SYMPTOMS OF ROOT-KNOT. 



The presence of root-knot becomes noticeable when the affected 

 plants become dwarfed or begin to die, but it is often present and 

 causing a great reduction in the crop yield without the grower's 

 knowledge. Indeed, it is probable that greater actual loss occurs 

 from the form of the disease where, to the untrained eye, no signs are 

 visible than in the case where the plants are actually killed, for a 

 farmer soon learns by experience not to plant in infected regions those 

 crops liable to total destruction, while he fails to notice a reduction in 

 yield, especially if the disease be well established and not a recent 

 introduction, so long as the affected plants do not show too great 

 dwarfing or discoloration. 



Aside from the killing or dwarfing of the plants in severe cases 

 or the reduction of yield in less serious infections there are no very 

 noticeable symptoms apparent on those parts of the plant above 

 ground. If rainfall has been rather scanty during the summer, the 

 affected plants first show the lack of sufficient water, while sometimes 

 the wilting is apparent when the sun is hot, even with abundant soil 

 moisture. Occasionally no discoloration is noticeable, but usually 

 plants that are badly afTectcd shov,- a lighter shade of green than un- 

 affected plants. Since, however, the disease usually occupies large 

 areas when it has been long established, there would be no opportunity 

 ordinarily to compare affected with unaffected plants in mass, so that 

 this difference would be readily overlooked. 



On the roots, on the contrary, very marked structural changes 

 are apparent. Instead of being smooth and of uniform or slowly 



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