Several calls have come in this week regarding random yellow spots in cotton fields. While there are a multitude of things that may cause this, there seems to be an underlying theme in many cases. Everyone is aware of the rainfall we have received this year. As a result of season long moisture levels, oxygen supply to the roots was limited in some cases. In areas of fields where water tended to pool or drain toward, root growth was likely reduced. However, we have had instances where the upper portion of the soil profile has become deficient in water (due to lack of rainfall or intervals between rainfall events) in some areas of the state. When this occurs with a shallow or poorly rooted crop, you run into issues with water and nutrient uptake. In these cases, the plant cannot take up as much water and/or nutrients as it needs and cotton begins to turn different colors due to deficiencies.
Situations such as these can present several management challenges. First and foremost on most people’s minds is yield potential of these spots. Yield potential is likely reduced in these areas; however, you still need to manage the crop for maximum yield potential. If possible, cut back on PGR application rates in these areas in order to prevent additional growth limitations. Weed control can also be problematic, especially if you are running a layby rig. Keep in mind that some products have minimum height requirements which may preclude use in some of these areas. When this occurs, switch to an alternative product that will meet your needs yet fit the minimum crop size application requirements. Also keep in mind that if these areas are in a small portion of the field, do not sacrifice management in 90% of the field for 10% of the field. Irrigate the field as needed based on the growth of the majority of the field. Do not over water the field trying to get these spots to catch up especially if they are on a small portion of the field.