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The use of plant growth regulators (PGRs) is an important tool to help manage cotton growth in moderate- to high-yielding environments. Proper use of PGRs can help balance vegetative and reproductive growth, in turn controlling plant maturity, improving square and boll retention, and controlling plant height to improve harvest efficiency. Cotton varietal growth habit and PGR response is one of the most important factors in developing a growth management strategy.
Mepiquat chloride, first sold as Pix® brand, was the first PGR successfully used to manage plant growth and yield.1 Mepiquat pentaborate, marketed as Pentia®, is also used to control plant growth. Both PGR products contain mepiquat which is an anti-gibberellin growth retardant used to reduce plant cell enlargement to help balance vegetative and reproductive growth. When applied to cotton, it can reduce stem elongation at newly formed internodes and can improve fruit retention. Growth regulators may be used to help make cotton mature earlier, Mepiquat applications have been linked to increased cotton yield potential when applied at the optimum rate and timing specific to a cotton variety and field conditions.2
It is important to understand the growth habit of a particular variety in order to manage vegetative growth. Certain varieties maintain an aggressive growth pattern when compared to others, and mepiquat rates and timing must be managed accordingly.
The Deltapine® cotton varieties may each respond a little differently to the application of mepiquat. The projected response of each variety is provided in Table 1. DP 1820 B3XF, DP 1822 XF, DP 1725 B2XF, DP 1614 B2XF, DP 1612 B2XF, DP 1518 B2XF, and DP 1725 B2XF have shown the most response to mepiquat, meaning lower rates or fewer applications may be needed. DP 1851 B3XF, DP 1840 B3XF, DP 1823NR B2XF, DP 1747NR B2XF, DP 1558NR B2XF, DP 1555 B2XF, DP 1549 B2XF, DP 1538 B2XF, DP 1454NR B2XF, DP 1359 B2RF, and DP 1219 B2RF have shown the least response to mepiquat, meaning timely early-season applications at higher rates or multiple applications may be needed to control vegetative growth. Although local soil and management issues may impact PGR applications, consider the following guidelines for cotton varieties in the moderately and least responsive categories. Growers should plan to apply mepiquat at 8 to10 nodes (match-head square) and aggressively apply mepiquat if there is a history of rank growth, or if the crop received early rainfall or was rotated behind a crop where excessive nitrogen was applied. Mismanagement of mepiquat or other PGRs can have a negative effect on yield potential, especially when applied too early, when applied to stressed cotton, or when applied to a determinant cotton variety.
When deciding to apply an application of Pix, the actively-growing top 5 internodes of the cotton plant should be evaluated.1 Mepiquat chloride rate and timing sticks are available to provide recommendations according to the average internode length of the top 5 nodes of the plant. Another way to determine application rate is to monitor the height and internode distance between the 4th and 5th node below the terminal node. For areas with a high average annual rainfall, Pix application rates are based on the internode distance between the 4th and 5th node and the total mainstem node number. The longer the internode length, the higher the recommended rate.
Variety response to PGR applications varies greatly among the Deltapine cotton varieties. Knowing the response of a variety to PGRs can help growers properly manage growth to improve cotton yield potential and harvest efficiencies. For varieties that are less responsive to PGR applications, timely early-season applications at higher rates or more applications may be needed to control growth.
Sources: 1Jost, P., Whitaker, J., Brown, S., and Bednarz, C. Use of plant growth regulators as a management tool in cotton. The University of Georgia Cooperative Extension. http://www.caes.uga.edu/. 2Oosterhuis, D. and Robertson, W. The use of plant growth regulators and other additives in cotton production. University of Arkansas. AAES Special Report 198. Proceeding of the 2000 Cotton Research Meeting. http://www.uark.edu/.130423013704
<p><small>Sources: 1Jost, P., Whitaker, J., Brown, S., and Bednarz, C. Use of plant growth regulators as a management tool in cotton. The University of Georgia Cooperative Extension. http://www.caes.uga.edu/. 2Oosterhuis, D. and Robertson, W. The use of plant growth regulators and other additives in cotton production. University of Arkansas. AAES Special Report 198. Proceeding of the 2000 Cotton Research Meeting. http://www.uark.edu/.130423013704