Cotton Irrigation Termination Decisions
David Hall, Extension Water Educator, Cale Cloud, Extension Water Agent, and Wesley Porter, Extension Precision Ag and Irrigation Specialist:
As we approach the end of the growing season we are around 12 to 16 weeks after planting at the beginning of September based on a May 1 to June 1 planting. On average, we will be around 14 to 18 weeks after planting throughout the month of September. This will put our water usage just past peak and beginning to decline. UGA Extension cotton irrigation scheduling guidelines, like all other guides, must be used in conjunction with field and atmospheric conditions. That means boots on the ground or moisture sensors to assist you in determining available moisture in the soil. September is historically dry with low humidity leading to soils drying out faster. Although cotton plant moisture uptake is small, there still is a need for some moisture in the soil to aid in finishing out those last harvestable bolls. As water use declines, it is necessary to closely monitor your fields for cotton bolls that are beginning to open. UGA’s official irrigation termination recommendation for cotton is at an average of 10% open boll across a field. 10 percent open is not a high number of bolls that are open to start considering irrigation termination. A plant with 12 harvestable bolls means you need to be looking at the available soil moisture if 1.2 bolls are open. As we continue to receive rainfall and have high humidity environments, boll rot is a major issue occurring across the state. This time of season extending leaf wetness period is going to make disease issues worse on both cotton and peanuts, so do everything you can to reduce these periods of wetness. The main point for irrigation termination on cotton is upon reaching that 10% open boll stage, do not over irrigate and exacerbate more boll rot, observe the current and long term weather forecast, know your soil moisture content and use good judgement on terminating irrigation. Good moisture in the soil and 10% open bolls means the end of another irrigation cotton season!