What are plant growth regulators?

Plant growth regulators (PGRs) are crop protection products used in a wide variety of crops worldwide to modify plant growth by interfering with plant hormones.

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The following types of hormones can be found in a plant:

1. Hormones that stimulate plant growth


Auxin hormones are commonly found in the growing regions of the plant such as the tip of the leaves, the tip of the shoot, or the buds. When auxins accumulate in the plant cell, the cells of the plant growing regions elongate, i.e., grow taller.


Gibberellins also cause cell elongation but are usually concentrated on the stem in the areas where new leaves, also known as nodes, are formed. Under the effect of gibberellins, the stem between the nodes elongates, i.e., the internode distance becomes longer. The more gibberellins, the longer the plant.

Gibberellins also influence seed germination. A seed will only start growing when enough gibberellins accumulate.

Gibberellins are present across all growth stages of the plant. Their concentration is highest during periods of rapid growth (Feekes 4‒6, Zadoks 30‒32).


Cytokinins promote cell division. If cytokinins are present in one cell, they divide it into two cells. Cell division means new cells and the emergence of new leaves, fruits, branches (tillers), etc.

2. Hormones that inhibit plant growth

Abscisic acid

During periods of draught, abscisic acid will accumulate at cell borders to keep the stomata of the plant cells closed. Stomata are small openings in the leaf that allow it to breathe but simultaneously cause it to lose water. Another function of abscisic acid is to inhibit seed germination (e.g., until growing conditions are optimal).

3. Hormones associated with fruit ripening


Ethylene is a gas that, once released, breaks down the cell walls of a fruit, making them softer. Ethylene also helps release sugar, making fruit taste sweet. The most common use of ethylene is on bananas, commonly shipped green from country of origin and given ethylene treatment to ripen shortly before reaching supermarkets. In cereals, ethylene induces ripening and stops further growth in the plant.

How do plant growth regulators work?

Different plant growth regulators (PGRs) interfere with different plant hormones and have different effects on plant growth. Even if two PGRs target the same hormone, their underlying chemistry can interfere differently with the targeted plant hormone.

Mode of action of cereal PGRs registered in the United States
Adjust SL (proprietary chlormequat chloride) Trinexapac-ethyl Ethephon
Inhibits early stages of gibberellin biosynthesis to reduce plant height and increase stem thicknessInhibits late stages of gibberellin biosynthesis to reduce plant height and increase stem thicknessReleases ethylene to reduce crop height
Long residual activityShort residual activity
Has a slow onset of action, creating a more gradual response as CCC acts in the early stages of gibberellin biosynthesisHas a rapid onset of action as trinexapac-ethyl acts in the late stage of gibberellin synthesis
Formulated to work effectively at temperatures as low as 34°FHarsh field conditions at or following application timing can cause crop damage.Induces ripening and consequently stops further growth processes in a plant

Wheat growth stages and application timing of different plant growth regulators
Wheat growth stages and application timing

When to use plant growth regulators

A plant growth regulator can be a valuable cereal management tool for growers looking to:

  • Maximize yield potential
  • Protect investments on crop input
  • Improve harvest efficiency
  • Increase grain quality
  • Reduce disease risk
  • Reduce lodging risk
Evaluating your lodging risk
When am I at risk for root lodging? When am I at risk for stem lodging?
Cereal crops are planted late (backward crop), and the focus is to maximize tillers.Cereal crops are planted early and show lots of growth.
Season is wet, resulting in less compact soil conditions.Spring is warm, promoting lots of growth.
 Cereal fields are highly populated (due to overseeding or heavy nitrogen levels), resulting in weak stems.
Cereal variety is prone to lodging.
When working with high yield wheat management

PGRs can be applied via ground boom or aerial application. For specific uses and tank mixing, always read and follow label directions. For more user instructions on Adjust SL, go to Application recommendations.

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Certain statements may not be applicable in all geographical regions. Product labeling and associated claims may differ based on government requirements.
Pending EPA registration, Adjust SL is not yet registered for sale or use in the U.S.