Cotton Growth Management: Focusing Growth with PGRs

Managing Growth

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13;10;There are several management options to choose from which can either stimulate plant growth or slow growth. Because each of these management practices needs to be tailored to the specific season, environment, and variety, a discussion of the components and the ways in which they can best be used is in order.

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Focusing Growth with Plant Growth Regulators

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13;10;Cotton plants are perennial plants that are grown and managed as annuals for crop production. Consequently, getting the plant to focus on reproductive growth is one of the most important areas of management.

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Both vegetative and reproductive growth play important roles in final yield. Vegetative growth may sometimes be considered a negative when striving for high yield, but it is important to remember that a plant must add leaves to add more squares. It is important to monitor plant height to a desired internode length (usually an average of 2 inches). Certain varieties with aggressive vegetative growth may require higher rates of PGRs (6 to 12 oz) as early as the 8 to 10 node stage.

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Conditions which should signal attention to possible applications include:13;10;

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  • Cotton rotated with corn
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  • Late-planted or late-maturing cotton

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  • Tall, vigorous, indeterminate cotton varieties

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  • Fields in which cotton tends to grow rank

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  • Thick stands

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  • Fields with high nitrogen availability, high application rates
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  • Fields to be first defoliated and harvested

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  • Fields with low square retention

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  • Irrigated fields
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Plant Growth Regulator Use

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13;10;The use of plant growth regulators (PGRs) can be a valuable tool in managing growth and controlling the distribution of vegetative and reproductive growth. Determining when to apply PGRs and at what rate can be difficult, so it’s important to understand how the products work.

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The Plant Growth Regulator Guide (Slide Rule) can be used to help determine the rate of plant growth and if a PGR application is needed. By factoring in the average number of mainstem nodes for a field and the internode distance between the 4th and 5th mainstem node, a growth rate can be determined (Very Slow, Slow, Normal, High or Very High). By inputting the average plant height for a field and the growth, the slide rule will suggest a PGR rate.

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PGRs have a number of effects on cotton growth and development. One of the most important effects is the 
reduction of internode elongation which can lead to cotton plants that are shorter and more compact. This can lead to carbohydrates being freed up for boll and square development.

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Efficacy of plant growth management depends primarily on the concentration of PGR in the cotton plant. As PGR rates increase, the concentration in the plant increases. This is why applying too much to small plants may result in unacceptable levels of stunting. As cotton plants get larger, the amount of PGR required to give an effective concentration in the plant also increases. If a plant is very large when normal rates are applied, the concentration will be insufficient to provide good growth control. This is why, especially with vigorous varieties, it is important to evaluate the growth rate of the crop and apply appropriate mepiquat chloride rates to adjust growth, if it has become excessive.

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simple — yet highly accurate — method of monitoring cotton growth. The procedure involves determining the length of the most recent mature, fully-expanded internode which is between the fourth and fifth node from the terminal of the plant. The term “maximum internode distance65533;? (MID) refers to this measurement.

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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.​​​​​