The growing environment in this large cotton production region (~ 6 million acres) is more diverse than across the entire cottonbelt. Planting begins in early-to-mid February in the lower Rio Grande Valley and continues through May and often into June on the High Plains. Boll development, therefore, occurs under very hot, dry conditions during June-August in South and Central Texas and under cooler temperatures (August-September) in the Rolling and High Plains. July and August are typically hot and relatively dry across the entire state. Only 30-35% of the total cotton acreage in Texas is capable of supplemental irrigation and even those acres do not have enough water to provide 100% of the crop water use. Therefore plant water stress is the single greatest limitation to productivity. Both water supply and temperature conditions during the boll-filling phase of development affect lint quality. High temperatures coupled with water stress during boll filling result in relatively short fibers with high micronaire in Central and South Texas. Cool temperatures during September result in low micronaire many years on the High Plains.