144 FIELD CROPS FOR THE COTTON-BELT 



most injurious in the Houston clay or black waxy soils 

 of the southwest. This soil is usually quite compact and 

 often poorly aerated, a condition which seems favorable 

 to the development of the fimgus causing this disease. 



Root-rot occurs on many plants other than cottf®n, 

 such as alfalfa, cowpeas, sweet potatoes, and a rather 

 large number of dicotyledonous weeds. It does not, 

 however, seem to occur upon monocotyledonous plants, 

 such as corn, sorghums, the small-grains, and grasses. 



176. Cause. — Cotton root-rot is caused by a fungus 

 parasite which lives and spreads in the soil. Very httle 

 seems to be known about this infection or the progressive 

 stages of the disease. The myceUum penetrates the bark 

 and also the wood of the roots but it does not usually 

 extend into the wood far above the surface of the soil. 



177. Symptoms. — The presence of this disease is 

 usually first noticed by the sudden wilting and dying of 

 the cotton plants. An examination of the root-system 

 of the diseased plant will show that the rootlets and ex- 

 ternal surface of the roots have been destroyed. The 

 fungus also invades the fibro-vascular system of the under- 

 groimd parts of the plant. The siu-face of the diseased 

 roots is usually covered with dirty yellowish strands or 

 thin wefts of the fungus filaments. While a few plants 

 are sometimes killed by this disease during the early 

 stages of their growth, they are far more commonly killed 

 after some of the bolls begin to mature. 



178. Remedies. — ■ As this disease thrives best in an 

 unaerated soil, remedial measures are based largely on 

 the principle that air must circulate freely through the 

 soil. Where possible, deep fall plowing is advisable. 

 Investigations conducted near Luling, Texas, by the 

 Bureau of Plant Industry, Washington, D. C, indicate 



