Factors influencing the development of cotton diseases

The observations and experiments reported in the present paper were carried out in Suinin, Szechuan Province, West China, through the period 1938-41. Under local conditions, the incidence of most cotton diseases was observed to be influenced chiefly by air humidity. No matter whether it attacks the seedlings, mature plants, or bolls, such a disease requires a humid condition preceding the occurrence of an epidemic. For sore shin disease, soil moisture and soil temperature, however, have a more profound influence. Cyrtosis, which is a disorder caused by leafhopper injury, responds to the climatic factors in a different way. During the period of rapid reproduction of the leafhopper, higher temperatures result in the earlier appearance of the disease, while heavy rainfalls reduce the intensity.
Modification of the environmental conditions by varying the time of sowing influences the incidence of diseases occurring in both the seedling and mature stages of the cotton plant. Among seedling diseases, anthracnose is further proved to be influenced chiefly by air humidity in its prevalence. Sore shin disease, on the other hand, requires a moist soil condition for its spread and development. In the mature plant, late sowing increases the intensity of cyrtosis but reduces that of bacterial blight and anthracnose.
Modification of several cultural practices was also tested. Nitrogenous fertilizers generally increase the incidence of most diseases. Denser stand and closer spacing bring about a heavier infection in stem and leaf diseases but not in boll diseases. A mixed cropping system appears to have no effect on the fungal and bacterial diseases but reduces the intensity of cyrtosis when the crop interplanted with cotton is not susceptible to the infestation of leafhopper.