The Bulletin. 9 



shin," and occasionally by other damping-off organisms ; and it is difficult 

 to describe the differences between these and the effects of anthracnose 

 on seedling plants. 



Cause. — The disease is caused by the fungus Glomerella (Colleto- 

 trichum) gossypii. It may develop inconspicuously on leaf-scars, or 

 other weakened tissues of the cotton plant. In partially affected bolls it 

 may enter the seeds, and will remain dormant in them for several years, 

 resuming its growth when the seeds germinate. 



Dissemination.- — Seeds from infected bolls are infected internally, and 

 are the chief means of dissemination. External contamination of the 

 seeds by spores may occur from the dripping or splattering of rain- 

 drops from affected to sound parts of the plant, or by ginning with 

 machinery that has become contaminated. Because the spores are 

 sticky, and are not easily dislodged when dry, wind does not play an 

 important part in spreading the disease, and it spreads rather slowly 

 from plant to plant in the field. The fungus may persist on old affected 

 stalks in the field for about a year. 



Infection. — Bolls may be infected at any time from the blossoming 

 period until they are almost grown. Moist conditions are necessary for 

 this to occur, and the disease is most serious, other things being equal, 

 in wet seasons, or even in the moister parts of a field. Cotton varieties 

 show differences in natural susceptibility ; but often the differences noted 

 in the amount of disease in varieties are due mainly to differences in the 

 chances for seed infection the previous year. 



Control. — The main thing is to avoid planting infected seed. Unse- 

 lected seed from a field where the disease has existed will carry the infec- 

 tion. Seed should not be brought from a distance unless assurance can 

 be had of its freedom from infection. No seed treatment can success- 

 fully reach the internal infection, and disinfection of the exterior merely 

 is not worth while as a general practice. Seed safe for planting can be 

 secured from a moderately infected field by marking stalks that are not 

 affected and are some yards away from diseased plants, picking these 

 separately, and ginning with a well cleaned gin. If only a small lot of 

 seed can be secured in this way it can be used for starting a seed plat 

 from which clean seed for the general planting can be had the second 

 year. The sound seed must be planted where diseased cotton did not 

 grow the year before; or if necessary to plant cotton in the same field, 

 fall plowing to bury the stalks will render it safe. There is no evidence 

 that cotton seed or cottonseed meal used as fertilizer, or that stable ma- 

 nure plays any important part in the spread of the disease. It does not 

 persist in the soil. Some hold that if infected seed is kept until the 

 second season it will be reasonably safe to plant ; but this matter needs 

 further testing. 



COTTON "RUST." 



Distribution. — This disease is common in light sandy lands of the 

 North Carolina cotton belt. 



Cotton is the only crop affected. 



The disease is also known as black rust and leaf blight. The name 

 "rust" is somewhat objectionable because it refers more appropriately to 

 diseases caused by the true rust group of fungi. 



