OPTIMIZING PLANT GROWTH REGULATOR (PGR) USE IN COTTON

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The PhytoGen agronomy team continually evaluates the latest PGR research and conducts trials to evaluate PGR recommendations for PhytoGen® brand varieties.

Sometimes it pays to question and rethink even the most routine management decisions. Plant growth regulators (PGRs) are commonly used to manage vegetative growth and increase yields. Mepiquat chloride is the most popular PGR in cotton production due to its effectiveness and return on investment.

Mepiquat chloride applications inhibit cell elongation, reducing internode length and overall plant height. With less vegetative growth, plants focus energy on fruit set and boll fill — two mechanisms that can increase yield potential.

Although mepiquat chloride is a common crop input, often there is confusion about application timing and rates. It’s possible to stunt plants and reduce yield potential if mepiquat chloride is applied too early or when plants are stressed by drought or other factors. To further complicate application decisions, cotton varieties differ in their response to mepiquat chloride rates.

The PhytoGen agronomy team continually evaluates the latest PGR research and conducts trials to evaluate PGR recommendations for PhytoGen^® brand varieties.

Consider these tips to help optimize PGR applications and maximize yield potential:

Know the variety’s PGR response. Varieties respond to PGRs differently. For example, PhytoGen^® brand PHY 400 W3FE has a high PGR response rate while PhytoGen brand PHY 443 W3FE has a low rate. Dial in rates according to variety needs. For specific recommendations, check with your local cotton development specialist.
PGR decisions are made with dirty boots. No two fields are the same, so consider these questions before making PGR applications. Is the field irrigated or dryland? Stressed or actively growing? What is the plant height, node count and leaf size? Are plants beginning to put on squares, or are plants in early bloom? PGRs require a prescriptive approach for each field.
Pay close attention to internodes. Estimate vegetative potential by measuring internode length (the distance between two successive branches off the main stem). Measure the first fully expanded internode, typically between the fourth and fifth nodes from the top of the plant. Use the ranges below to gauge current growth rate:
- Low:. 5- to 1-inch internode
- Medium: 1- to 2-inch internode
- High: 2-inch (or more) internode
Less sometimes is more. Many PhytoGen brand varieties require less PGR than competitive varieties. Too much PGR, especially too early in the season, could lower yields. Check with your local PhytoGen team on specific recommendations. You could save on input costs and increase yield.

The charts below show how plant height and yield correlate to low (60 oz.), moderate (72 oz.) and high (84 oz.) season totals of mepiquat chloride. In the first graph (Figure 1), an increase in mepiquat chloride rates correlated with decreased plant height.

Across the three PGR regimens, the low and moderate mepiquat chloride rates maintained high yield potential while the high rate significantly reduced lint yield with all varieties (Figure 2).

PGR recommendations are highly dependent on variety and field conditions. If you've planted competitive brands in the past, your PhytoGen brand varieties may benefit from lower PGR rates than you are accustomed to applying. That said, the old adage is still true: PGRs can slow plant growth, but they will never shrink a plant.

Our team Is available to visit with you after planting to discuss PGR rates and help make PGR recommendations for varieties in your geography.

For questions about PGRs or other agronomic issues, contact your local PhytoGen team at https://phytogen.com/team.

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