Naturally occurring or synthetic substance which influences plant development or reproduction but has no nutritive value.

A substance applied to cotton plants which affects growth or senescence (e.g., Pix and Prep); abbreviated PGR.

See Growth Regulator.

A substance used for controlling or modifying plant growth processes without appreciable phytotoxic effect at the dosage applied.

An organic compound, either natural or synthetic, and other than a nutrient, that modifies or controls one or more specific physiological processes within a plant.

A substance that alters the expected growth, flowering or reproduction rate of plants. Fertilizers and other plant nutrients are excluded from this definition.