Square Set and Retention

After about 350 to 450 DD60s, which is usually 30 to 45 days after planting, cotton begins to produce squares (flower buds) which have the potential to become a boll. Squares are usually subjectively described by their size — pinhead, match head, small, medium and large — and entomologists and agronomists frequently differ on when a bud is large enough to be considered a square. From a plant monitoring view, many people like to define the minimum size a square needs to be as that time when the actual flower bud, not including the bracts, is 1/8 inch in diameter. From a total cotton management standpoint, this is too long to wait, because the square at that stage has been susceptible to shed.

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Not all squares on a cotton plant make it to open bolls, as square retention on the very first fruiting branch is typically less than the three to four branches above it. There is also typically only 25 to 60 percent retention of first position squares on fruiting branches 10 through 12. When first position square retention in the top five fruiting branches falls below 80%, this can be a cause for concern due to insect damage or lack of moisture.

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Grower Tip: Determine first position fruit retention in the first 10 branches by dividing the number of fruit by the number of fruiting sites. At least 20 plants should be mapped to get a valid rate.

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Prior to the end of the second week of bloom, there is not enough of a boll load for physiological stress (lack of carbohydrate supply) to be a factor in square retention. Extended periods of cloudy weather during squaring, very early bloom, or severe cold or drought stress cause physiological shed. Therefore, physiological shed is not usually an important factor early in the season, but it is important to focus on other reasons. If shedding is not caused by temperature, clouds or moisture, then it is most likely caused by insects and corrective measures should be employed.

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Insects can cause square damage or shed. Reduced bollworm sprays in Genuity® Bollgard II® cotton fields may allow plant bugs to survive. Yield and earliness benefits of transgenic cotton would be reduced if plant bugs are allowed to damage squares. Thus, it is critical to maintain a thorough full-season insect and square retention scouting program to achieve full benefit from this technology.

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This article is from the Cotton Management Guide, a publication with year-round advice on managing high-yielding cotton. Download the Deltapine Cotton Management Guide now or sign up for new content to be delivered to your email each month.​​​

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