Diseases and Production Problems of Cotton in Arizona

Many different cultivars of cotton are grown in various ecological areas in Arizona. Production areas vary greatly in elevation and annual rainfall. At one extreme is the Yuma Valley in the southwestern corner of Arizona along the lower Colorado River where cotton is planted in the latter part of February. Elevations here are approximately 75-100 feet. In this area, average annual precipitation is less than 4 inches. In the southeastern part of Arizona in Graham, Cochise, and Greenlee counties, cotton is grown at elevations above 3,000 feet and plantings take place during the middle of April. In Cochise County, for example, cotton is grown in Pearce (4,375 feet), Cochise (4,212 feet), Bowie (3,765 feet) and San Simon (3,601 feet). The production areas along the Gila River in Graham and Greenlee counties are approximately 3,000 feet and 3,500 feet, respectively. At elevations of 4,000 feet, temperatures are approximately 12 o F lower (maximum and minimum daily temperatures) than temperatures at sea level. Also, there is a correlation in Arizona between elevation and rainfall. Low elevation production sites in the western part of Arizona average less than 4 inches of rain annually, whereas rainfall at Pearce (4,375 feet) is approximately 13-15 inches annually. Cotton is exposed to the so- called “monsoon” season during July, August, and September. This period is characterized by heavy, irregularly distributed rainfall and high humidity. Rainfall during this period at the higher elevations can range as high as 10-12 inches during certain summers. These temperature and rainfall differences play important roles in the distribution and severity of cotton diseases in Arizona.