Response of Deltapine® Cotton Varieties to Different Plant Growth Regulator Regimes



  • The plant growth regulator (PGR) mepiquat chloride benefits cotton production by helping to balance vegetative versus reproductive growth. The appropriate rate and timing of PGR applications are essential to the management of cotton varieties in the coastal U.S.

  • Each season a new set of candidate cotton varieties is introduced through the Deltapine® New Product Evaluator (NPE) program.

  • The primary objectives of this study were to:

    • Evaluate the growth habit of new cotton products in comparison with existing Deltapine® cotton products.
    • Evaluate the response of the new candidate varieties to mepiquat chloride application in three different application regimes.



Location Scott, MS Planting Date 5/17/19
Soil Type Silt Loam - mixed Harvest Date 10/9/19
Previous Crop Corn
Potential Yield
Tillage Type Conventional
Seeding Rate


  • This study was set up to encourage excessive vegetative growth due to strong background fertility levels, the previous corn crop, irrigation, and relatively high rates of nitrogen fertility (120 lb/acre of actual nitrogen applied as 28% liquid UAN in furrow at layby). 
  • Deltapine cotton products tested included Bollgard II® XtendFlex® cotton (B2XF) and Bollgard® 3 XtendFlex® cotton (B3XF). Bollgard II XtendFlex cotton provides tolerance to dicamba, glyphosate, and glufosinate herbicides and protection from cotton feeding insects. Bollgard 3 XtendFlex cotton has 3 modes of action to protect against cotton pests and triple stacked herbicide tolerance to glyphosate, glufosinate, and dicamba. 
  • All other agronomic inputs (weed control, insect control, and irrigation) were per local standards for each treatment.
  • Trials were planted in strip plots 8 rows by 240 feet long with plot size approximately 0.15 acre.
  • Three application regimes of mepiquat chloride (standard 4.2% formulation) were applied as follows (Table 1):
    • An untreated check with no PGR applied.
    • Passively managed regime (representing older growth management methods) – three application rates and three timings totaling 38 oz/acre applied with delayed early application on July 14, 2019 at a reduced rate.
    • Aggressively managed regime – three applications at maximum label rates at three timings totaling 48 oz/acre applied.
  • Growth characteristics of new Deltapine cotton products were evaluated as follows:
    • End-of-season plant height indicating the growth nature of the new product.
    • Height reduction from either the passively or aggressively managed treatments versus the untreated check.
    • Evaluation of the effects of the PGR treatments on yield.



  • Varieties with a relatively high amount of height reduction are likely more sensitive to PGR applications and generally require less aggressive management. Understanding the nature of each cotton product helps in both proper placement and management decisions.

  • The tallest plants in this experiment were from the untreated plots and averaged 70 inches tall at the end of the season (Figure 2A). This is in contrast to 2018 where the tallest plants ended the season at 89 inches tall (Figure 2B). Compared to 2018, the environmental conditions of 2019 did not favor strong vegetative growth, resulting in less need for growth control.

  • A range of response (in height and height reduction) to PGR application was observed across this experiment (Figures 2A and 3). Several of the cotton varieties showed different levels of susceptibility to PGR application rates and timings.

  • When measured as a percent height reduction with similar rates and timings of PGR as were used in previous years of this study, a similar range of response was observed across cotton products with some products showing greater response to growth control (Figure 3).

  • The aggressive regime utilized the maximum labeled rate of 48 oz/acre split into three applications of 16 oz/acre. The earlier timing and higher application rates offered more power in growth control for some of the tested cotton varieties. Environmental conditions did not favor strong vegetative growth in 2019, resulting in some varieties experiencing yield loss with the aggressive PGR regime compared to the passive PGR regime.

  • As compared to previous years, cotton yield was considerably higher in all treatments in 2019.  Averaged across all products, the untreated plots yielded 1335 lb lint/acre (Figure 4A).  This contrasts with similar work in 2018 where the untreated plots averaged 653 lb lint/acre (Figure 4B). While environmental conditions were not conducive to excessive vegetative growth in 2019, they were ideal for boll retention and, when coupled with good harvest conditions, led to higher yields. 

  • Across all tested cotton products, the passive PGR application regime increased yield by 370 lb lint/acre over the untreated plots (Figure 4A).

  • The aggressive regime increased yield over the untreated plots by 218 lb lint/acre but were 152 lb lint/acre lower yielding than the passive regime (Figure 4A).

  • In 2019, earlier cotton maturities (DP 1725 B2XF brand and earlier) had a reduction in yield potential in the aggressive PGR applications compared to later maturities (Figure 5). 
  • As represented in Figure 6, all plots in this trial produced relatively high yields with the lowest recorded yield being 1100 lb lint/acre and the highest yield recoded being approximately 2000 lb lint/acre.

  • As in previous years, the treatment resulting in the tallest plants (greater than 60 inches) in the trial was the lowest yielding, while the plants in the higher yielding plots were between 40 and 60 inches at the end of the season.

  • Contrasting to previous work, some of the more aggressively managed plots were lower yielding as compared to those less aggressively (passively) managed.  End-of-season plant height less than 40 inches typically was associated with reduced yield as compared to the plots with an end-of-season height between 40 and 60 inches.  

  • 2019 was a year where PGRs could have been overused (as in some of the aggressively managed plots) and continues to point out the need for variety characterization, proper/timely scouting, decision making, and PGR applications.




  • Both the NPE candidate cotton products and current commercial Deltapine® cotton products had high yield potential in the Scott, MS location during 2019.

  • Correct PGR use is essential to optimize the growth habit of modern cotton products. 

  • Newer cotton products are typically more aggressive in growth habit than older ones, making the need for timely monitoring and growth control application critical to the success of a cotton field. As much as a two-fold difference in growth response to PGR applications was observed across the tested cotton products in 2019.  

  • Plant growth and monitoring are the best tools for use in making the decision to use a growth control application with historical varietal response being an additional consideration. 

  • Consult your local Bayer representatives for further information about Deltapine product placement and management for the 2020 season.



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