PGR Growth Regulators (3/3) Mode of use

Growth regulators are chemical compounds that alter or regulate grass growth. These products are essential in the maintenance of sports surfaces and green areas as they help to control turf growth, improve turf quality and density, and reduce the need for mowing.

However, it is important to consider the rebound effect, where the turf experiences accelerated growth once the effect of the regulator wears off. To avoid these rebounds, it is necessary to overlap treatments appropriately.

Mode of application

The application of growth regulators requires a precise strategy to maximise their efficacy and minimise rebound effects. Studies by Dr. William Kreuser and Dr. D. J. Soldat have established specific degree day intervals for the application of growth regulators. species C3 (such as Agrostis and Poa annua on greens):

*The range indicates low-high application rates.

For C4 species, the base temperature for the calculation of degree days is 10°C. For example, on Bermuda greens with an average temperature of 15°C, 10 units are subtracted from the average degree day, adjusting the application interval accordingly.

Effect of temperature

The effect of growth regulators can vary with temperature. Studies, such as those by Branham et al. indicate that turfgrasses break down these compounds more rapidly as temperature increases, reducing their effectiveness during the summer months. Dr Karl Danneberger demonstrated this with the use of Trinexapac-ethyl, noting that in spring and autumn, application intervals were 13 to 27 days, while in summer, the intervals were reduced to approximately 8 days.

Use of weather stations

Weather stations WatchDog are invaluable tools in the calculation of degree days, essential for the accurate management of turf and crop growth regulators. These stations provide real-time weather data, including daily maximum and minimum temperatures, allowing managers to accurately calculate cumulative degree days.

By having access to accurate and up-to-date information, it is possible to determine the optimal times for the application of growth regulators, avoiding the rebound effect and ensuring effective growth suppression.

Weather stations WatchDog not only facilitate the calculation of degree days, but also provide a disease and pest prediction model based on the continuous recording of key variables such as temperature, humidity and rainfall.

Practical applications of Grades Day

The calculation of degree days allows estimating the optimal time for the application of growth regulators, suppression of flowering on Poa annua, herbicide application pre-emergents, and avoid the rebound effect. It is a crucial tool for planning effective and timely treatments.

Recommendations for Use

How to apply?

1. Start and Rate Adjustment: Start at half the recommended rate and apply every two weeks until the desired level of regulation is achieved. Reduce the dose on the first application by 30% to avoid stress on the lawn.
2. Programming: Use the degree day method to schedule applications. It is advisable to apply some foliar nitrogen or iron to improve turf response.
3. Post-Application Irrigation: Water the lawn about 4 hours after application to wash the surfactant off the blades and avoid burns.
4. Specific Considerations:
   • Adjust application rate according to turf species and variety.
   • Avoid application on Zoysia or Paspalum grasses.
   • The maximum action of the regulator occurs after 20 days and is removed after 35 days.
   • The effect decreases more rapidly with increasing temperature.
   • Multiple applications are more effective than a single high dose.

Combination of regulators:

• Mixing Trinexapac with Paclobutrazol improves and prolongs the effect.
• Grass improves its photosynthetic efficiency, root-leaf ratio, and accumulation of reserves such as sugars and proteins.

Diseases:

• If the area has high disease pressure, apply fungicide along with the controller.

In conclusion, growth regulators are essential tools in turf management, especially on sports surfaces. Their correct application and choice according to the specific needs of each area can result in a turf of high quality, density and uniformity, facilitating its maintenance and improving its appearance and functionality.