Meta-Analysis of Deltapine® Cotton Variety Response to Plant Growth Regulators at the Bayer Learning Center at Scott, MS from 2011 through 2020



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

  • Each season new Deltapine® cotton varieties from across the cotton growing region are evaluated at the Bayer Learning Center at Scott, Mississippi for PGR application response and demand in the productive Delta system.

  • Differential responses to PGR applications have been observed each year among the Deltapine cotton varieties tested.

  • This is a summary of Deltapine cotton variety PGR application response data from 2011 through 2020. 



Location Scott, MS     
Soil Type  Commerce/Forestdale silt loam  



Planting Date May 1 or later    
Harvest Date Vary  

Potential Yield
Seeding Rate
41,000 to 



  • A total of 10 to 18 Deltapine® cotton varieties were tested each season.
  • These studies were set up to encourage excessive vegetative growth with strong background fertility levels, the previous corn crop, irrigation, and relatively high rates of nitrogen fertility (100 to 120 lb/acre of actual nitrogen soil applied as 32% liquid N). 
  • All other agronomic inputs (weed control, insect control and irrigation) were per local standards for each treatment.
  • There was no PGR trial in 2014 and no passive regime in the 2016 trial. 
  • All PGR plots were treated with labeled but varying rates and application timings of currently available mepiquat chloride (standard 4.2% formulation). These application rates and timings were used to separate differences in Deltapine cotton variety responses and not necessarily to provide specific guidance on PGR management for an individual field, farm, or variety. Application regimes (Table 1) included:
    • An untreated control with no PGR applied.
    • Passively managed regime (representing older growth management methods): three application rates and three timings totaling 34 to 38 oz/acre applied per season at delayed timing.  
    • Aggressively managed regime: three applications at a maximum label rates at three timings totaling 48 oz/acre applied per season.
image Table 1. Passive and aggressive PGR treatment rates and application timings.

  • Growth characteristics of Deltapine® cotton varieties tested were evaluated by:
    • Stand establishment: monitored for normal emergence (data not presented)
    • Plant growth: monitored in season
    • End-of-season plant height: 10 plants/plot measured at harvest 
    • Height reduction from either the passively or aggressively managed treatments versus the untreated check.
    • Representative turnouts from trials at the Scott Learning Center were used to estimate lint yield/acre to evaluate yield effects of PGR treatments.
  • Deltapine cotton variety sensitivity to PGRs – PGR application growth reduction was calculated as the percentage that plant height was reduced when compared to the untreated plot.
    • Cotton varieties were then characterized by the percent growth reduction to indicate PGR sensitivity within each year as either:
      • More Responsive – Cotton varieties considered more responsive were the top 50% of the Deltapine cotton varieties within the year tested.
      • Less Responsive– Cotton varieties considered less responsive were the bottom 50% of the Deltapine cotton varieties within the year tested.



image Figure 1. Average cotton plant height by PGR regime from 2011 through 2020.



  • All conclusions from this data are highly interactive with the production system and environmental conditions during each growing season and should be viewed as such.

  • The More Responsive cotton varieties demonstrated as much as 10% greater height reduction in the aggressive regime over the untreated checks when compared to the Less Responsive cotton varieties (Figure 1).

image Figure 2. Average cotton yield by PGR regime from 2011 through 2020.
  • The Less Responsive cotton varieties demonstrated slightly higher yield potential than the More Responsive cotton varieties in all PGR regimes (Figure 2).
image Figure 3. Linear regression of average lint yield versus average height in Less Responsive and More Responsive Deltapine® cotton varieties from 2011 through 2020 at the Scott Learning Center. (Student t-test was significant at P=0.0175).



  • The Less Responsive cotton varieties showed a statistically significantly greater decrease in average yield than the More Responsive cotton varieties in response to excessive height (Figure 3).
    • Differences in slope between categories:
    • Less Responsive= -27.78 lbs/inch
    • More Responsive = -20.11 lbs/inch
  • Approximately 15% more of the yield variability can be accounted for in height (as measured by R2) in the Less responsive cotton varieties. So, for each extra inch in height, the Less Responsive cotton varieties will lose an average additional 7.7 lbs lint yield per acre compared to the More Responsive cotton varieties. 

  • The yield response due to additional height is likely a function of the effect of the plant allocating energy to vegetative growth, the shading that occurs from neighboring plants, and associated fruit shed. Plants can also shade themselves as a result of excess height. An individual fruiting structure (squares particularly) is photosynthetically independent of the plant and if shaded, is more likely to shed just after bloom due to the lack of available sugar. Bolls are not independent, and the plant senses their need for sugar (to make carpals, seed and lint) hormonally. If it’s not there for whatever reason, the boll will shed in the week or so after bloom. That’s why this is all a big cascade of an effect. None of it occurs due to a single cause.

  • When creating management plans for Less Responsive cotton varieties, early and timely applications of PGRs at appropriate rates are even more important. 

  • When the cotton variety sensitivity to PGR is known, a management system can be built factoring in their growth tendencies. 

  • To obtain optimal value from the cotton varieties and the traits they contain, this information should be considered for every cotton variety, field, and farm.

image Figure 4A. Average Plant Height of Less Responsive Deltapine® cotton varieties by PGR regime from 2011 through 2020.
image Figure 4B. Average plant height of More Responsive Deltapine® cotton varieties by PGR regime from 2011 through 2020.
image Figure 5A. Average Lint Yield of Less Responsive Deltapine® cotton varieties by PGR regime from 2011 through 2020.
image Figure 5B. Average Lint Yield of More Responsive Deltapine® cotton varieties by PGR regime from 2011 through 2020.


  • PGR use in cotton crops is a tool that can be used to help manage excessive vegetative development and increase yield potential.

  • Significant differences exist in the response of Deltapine® cotton varieties to PGR application.

  • In Less Responsive cotton varieties, the negative response to excessive growth that can occur from inadequate rates of PGR application is greater than in More Responsive cotton varieties (Figure 3).

  • For this reason, understanding the PGR sensitivity of cotton varieties is essential in developing a management plan for the product planted on a given farm or field.

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