148 FIELD CROPS FOR THE COTTON-BELT 



plowing, and (3) the use of varieties least susceptible to 

 the disease. 



In dealing with anthracnose, one mxtst remember that 

 ^he fungus will live from one season to another in the seed; 

 therefore it is of supreme importance that planting seed 

 be secured from undiseased portions of the field. It has 

 also been proved that the anthracnose fungus can survive 

 in the field for at least a year on diseased bolls. It is there- 

 fore imperative that cotton is not grown two years in 

 succession on land infected with this disease. If some crop 

 other than cotton is grown on the land, the disease will 

 largely die out within one year. It seems that rather short 

 rotations are very effective in fighting this disease. ' 



Fall plowing and the growth of winter cover-crops tend 

 to reduce the prevalence of anthracnose. 



MOSAIC DISEASE 



187. Occurrence. — This disease is often known as 

 black-rust and yellow leaf-blight. It is rather common 

 throughout the cotton-belt, doing its greatest damage on 

 light wornout sandy soils or soils deficient in humus. 

 Under such conditions the yields of cotton are often re- 

 duced from 50 to 75 per cent as a resul,t of mosaic disease. 

 Any sudden check to active growth of the plants may in- 

 crease the prevalence of the disease. 



188. Cause. — Mosaic disease is termed a physiologi- 

 ical disease in that the fungi causing the trouble do not 

 usually attack thrifty and vigorous plants, but ohly those 

 plants that have been weakened as a result of unfavorable 

 conditions. Probably the three most important soil 

 factors responsible for the prevalence of mosaic disease 

 are (1) lack of humus, (2) lack of potash, and (3) lack of 

 drainage. 



