Dr Fred Yelverton, North Carolina State University
Plant growth regulators (PGRs) are widely used in all segments of turfgrass management. The term PGRs is descriptive; they are used to manage plant growth. PGRs can be grouped into two general categories: 1) Herbicide growth regulators and 2) True plant growth regulators. Herbicide growth regulators are typically used to reduce seedhead production and are used primarily in low maintenance turfgrasses such as highway rights-of-way and industrial sites. The products typically produce significant discoloration of turfgrasses. True PGRs are commonly used in highly maintained turfgrass such as golf courses and sports fields. These products include trinexapac-ethyl (Primo), paclobutrazol, flurprimidol, and ethephon. These products are used to suppress vegetative growth and improve turfgrass quality. Discoloration from these products is usually minimal. Trinexapac-ethyl, paclobutrazol, and flurprimidol reduce vegetative growth by a temporary inhibition of gibberellins in plants. Gibberellins are naturally occurring plant hormones that are responsible for cell elongation (among other things). Once the products are taken up into plants, the gibberellin biosynthesis pathway is interrupted and cell elongation is inhibited. The result is a more compact plant that requires less mowing. Data show these products can reduce plant growth by 50% or sometimes even more. This translates into significant mowing reduction that is a significant management tool for turfgrasses. Ethephon works by altering ethylene production in plants. This product can be used for seedhead reduction in plants and is specifically used for seedhead reduction of Poa annua.
