Consider Irrigating to Finish Out the Top Crop (Collins & Edmisten)

By Guy Collins

Last effective blooming can be a moving target from year to year, and across geographies within our state, and it largely depends on Fall weather. In years where we experience sunny, warm conditions during September and October (similar to that of the Fall 2019), our last effective blooming can extend to September 1st or a little beyond. In years where we experience cloudy and/or cooler weather during September and October (similar to that of Fall 2020), our last effective blooming can be as early as August 15 or 20. Generally speaking, on average, our last effective bloom dates occur around August 25, therefore this week (August 23–27) should mark the end of our effective blooming period unless we have a fairly warm, sunny Fall. Blooms that occur beyond this week have a diminishing chance of becoming harvestable, therefore the bolls on the plant as of now are likely the last ones that we can reasonably harvest.

Growers can flag a few white blooms on plants in some fields (or parts of fields) in order to know which bolls have a reasonable chance of being harvestable when making defoliation decisions later in the season. It will be important to remove any plastic flagging before harvest to avoid contamination issues.

The number of days between our last rain and today naturally varies within the state. With that said, there were visible signs of wilting in some places today (August 27, 2021) and somewhat earlier this week in other areas of the state. Other places do not show any signs of wilting, especially in areas with heavier soils or where it has been a short time since the last rainfall. It’s amazing what a week or less of dry weather with temperatures in the mid-90s can do, regardless of rain amounts, and this really illustrates the point that we are never more than 4-to-5 days away from a potentially serious drought.

It will be important to monitor fields for drought stress independently, as response to drought is affected by boll load, root system, planting date / stage of growth, etc. In cases where cotton was planted in late May or early June, AND still has young bolls that are retained and are harvestable, you may want to consider irrigating these fields with 0.5″ in one or two irrigations until we receive rain again. The same applies to earlier planted cotton that has a strong top-crop with several young, developing bolls. Previous research that we’ve conducted illustrates that yields can be improved when the aforementioned scenarios occur. Although it is a loose correlation, generally speaking, 12 bolls per foot of row (on 36″ rows) comprise one bale/acre, which could provide some insight to how much the number of younger bolls COULD be worth at harvest. If upper bolls have filled out well and are larger, AND/OR there are no signs of wilting, irrigation isn’t necessary.

The hot, dry conditions that we are now experiencing in places have already opened a few bolls, more commonly in early planted cotton. This comes as no surprise. Generally speaking, we advise that irrigation should be terminated when 10 to 20 percent of bolls are opened or cracked, OR when conditions are favorable for hardlocking and boll rot (prolonged periods of cloudy, damp/wet soils, foggy or overcast conditions).