Response of Deltapine® Cotton Varieties to Plant Growth Regulator Applications
The plant growth regulator (PGR) mepiquat chloride benefits cotton production by helping to balance vegetative vs. reproductive growth. PGR applications of the appropriate timing and rate are essential to the management of cotton varieties in the coastal U.S.
The primary objectives of this study were to:
— Evaluate the growth habit of new cotton varieties – i.e. how tall is the variety without growth control.
— Evaluate the response of the varieties to mepiquat chloride application.
— Evaluate how aggressive (in both rate and timing) growth control applications should be for each of the tested products.
This study will help develop information so growers can best use new varieties when they enter the market.
Research Site Details
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 (130 lb/acre of actual nitrogen).
All other agronomic inputs were per local standards.
Application regimes of mepiquat chloride (standard 4.2% formulation) were 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 36 oz/acre applied with a delayed early application on June 30, 2018, 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 varieties were evaluated as follows:
— End-of-season plant height indicating the growth nature of the new variety.
— Height reduction from either the passively or aggressively managed treatments versus the untreated check, which did not receive a PGR application.
— Evaluation of the yield effects of PGR treatments used on all cotton varieties.
Understanding the Results
The 2018 growing season favored strong vegetative growth and high yield potential.
Averaged across all varieties, the average plant height of the untreated plots was 79 inches. The passive regime reduced the height by an average of 18.3 inches compared to the untreated control. The aggressive regime resulted in an average height reduction of 27.2 inches compared to the untreated control and an average height reduction of 8.9 inches compared to the passive regime (Figure 1).
Cotton varieties can vary in their growth response to PGR application rates and timings. In general, varieties with the most vegetative growth potential require intensive PGR management.
In this demonstration, the passive regime had an overall reduced rate and later timing of PGR application but still showed an average of a 22% reduction in height compared to the untreated plants.
The aggressive regime utilized the maximum labeled rate of 48 oz/acre split into three different applications of 16 oz/ acre. With the aggressive regime, the average height reduction was 34%. The earlier timing and higher application rates offered more power in growth control for the varieties tested.
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 variety helps in both proper placement and management decisions.
When averaged over all cotton varieties, the untreated plots had an average yield of 652.7 lb lint/acre. Both the passive and aggressive regime applications greatly increased yields with the highest yields being in the aggressively managed plots (Figure 4 and 5).
In this 2018 demonstration study, 67% of the yield variability can be accounted for in plant height (Figure 6). Taller plants yielded less. Treating with mepiquat chloride resulted in a more balanced vegetative and reproductive growth pattern.
What Does This Mean for Your Farm?
Correct PGR use is essential to optimize the growth habit of modern cotton varieties.
This study showed that well-timed, earlier applications of higher rates were better than the older techniques used in timing applications.
Newer cotton varieties 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. Applying those controls earlier is generally better and higher rates of mepiquat chloride (up to 16 oz/acre) are often needed.
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 needed consideration.