PGR Growth regulators (2/3) Classes and classification

Growth Regulators

Growth regulators are chemical compounds that alter or regulate the growth or behaviour of turf. 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. There are several classes of growth regulators, classified according to their mode of action and the type of uptake they have on plants.

Classification of Growth Regulators

Growth regulators are mainly classified into two types, according to their mode of absorption and their action on gibberellic acid, a plant hormone that promotes plant growth and development.

• Root absorption: This type includes compounds such as paclobutrazol and prohexadione calcium. Paclobutrazol is known to be the most aggressive and long-lasting of the growth regulators. Prohexadione calcium is also effective, although its action may vary depending on environmental conditions and turf species. Both compounds inhibit early gibberellic acid biosynthesis, resulting in a significant reduction in turfgrass growth.

• Absorption by the whole plant: This includes trinexapac-ethyl, which has a less intense and less long-lasting effect compared to the root-absorbed regulators. However, it is also characterised by a lesser rebound effect. This compound inhibits the biosynthesis of gibberellic acid in its final phase, which helps to keep grass growth under control.

Classes of Growth Regulators

There are five main classes of growth regulators, each with specific characteristics according to their mode of action and absorption.

Class A: Trinexapac-ethyl

Trinexapac-ethyl is a foliar uptake growth regulator that inhibits late stage gibberellic acid biosynthesis. It is most commonly used on sports surfaces because of its significant benefits: it reduces the need for mowing, increases turf uniformity and density, and improves the overall quality of the green area.

Class B: Paclobutrazol, Prohexadione Calcium, Flurprimidol

These regulators, absorbed by the root, inhibit the biosynthesis of gibberellic acid in its initial phase. They are effective in eliminating Poa annua on Agrostis greens, helping to maintain the purity and quality of turf on golf courses and other sports fields. Paclobutrazol is the most aggressive and long-lasting, while prohexadione calcium offers a less aggressive but still effective option.

Class C: Mefluidide

Mefluidide is taken up by both leaves and roots and acts by inhibiting cell division in meristematic tissue. Its use is indicated to reduce seed head formation, which is essential to maintain a uniform and aesthetic appearance of the turf.

D: Methyl-sulfometuron and Glyphosate

These foliar-absorbed compounds are herbicides which, when used at low doses, can reduce the growth of some species present on sports surfaces. This helps maintain the dominance of the desired species and reduces competition for nutrients and space.

Class E: Ethephon and Gibberellic acid

These are either synthetically produced phytohormones or compounds that hydrolyse phytohormones. Ethephon, for example, generates ethylene and its main use is seed killing in Poa annua. Its application is recommended during all seasons, as it increases density, directs growth well and improves the vigour of the turf during summer stress. In spring, mefluidide is mainly used.

Strategies for the use of growth regulators

In the management of new greens in AgrostisAn effective strategy is the use of paclobutrazol to control the Poa annua. On old Agrostis greens heavily contaminated with Poa annua, it is recommended to use ethephon to invigorate the lawn. In both cases, it is recommended to use trinexapac-ethyl to increase turfgrass vigour and control excessive growth. Prohexadione calcium can also be used as a less aggressive alternative to paclobutrazol, providing effective growth control without the more severe long-term effects.

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.