Formulations of Herbicides

Herbicides in natural state may be solid or liquid, volatile or non-volatile, soluble or insoluble. Most of the herbicides molecules in their natural state are, therefore, difficult to apply.

The active ingredient in a herbicide is the chemical that controls the target weed. The herbicide product is rarely made up only of active ingredients. Often the herbicide is diluted in water or a petroleum solvent, and other chemicals are added before the product is offered for sale. These other chemicals may include wetting agents, spreaders, stickers, extenders, or diluents. They usually make the product easier to apply and more convenient to handle. This mixture of active and inert ingredients (inactive) is called a formulation.

The two major objectives of formulating herbicides are to ensure –

  1. ease of handling and
  2. high controlled activity on the target plants.

A. Water soluble concentrate (SC) 

Soluble liquid (SL)

Formulations are in the form of soluble liquids. It is a physically homogeneous mixture of herbicide concentrate and the carrier (usually water). E.g., Amine salts of 2,4-D, 2,4 5-T, diquat, paraquat and isopropylamine salt of glyphosate and imazethapyr.

Soluble powder (SP)

The formulation is dry and consists of the active ingredient and additives. Soluble powder formulations are similar to solutions (S), When mixed with water, these dry formulations dissolve readily and form a true solution.

Soluble granules (SG)

Soluble granules are dry and larger particle size than soluble powder. They are soluble salts of various compounds. Typical formulation contain 40 to 95 % active ingredient.

B. Emulsifiable concentrate (EC)

The ingredient is dissolved in solvent and an emulsifier is added to it. Since the emulsifier helps in uniform distribution of the chemical in water, no stirring is necessary while spraying. Eg. 2,4-D ester, Alachlor, Nitrofen, Diallate.

Gels (GL)

Gels are relatively new products that are thickened emulsifiable concentrate packed in water soluble bags.

C. Wettable powders (WP)

In an herbicide suspension the fine particles of the wettable powder are dispersed in a suitable carrier.

E.g. atrazine 80% WP, diuron 80% WP, and isoproturon 70% WP and almix20% WP.

D. Dry flowables (DF) or Water dispersible granules (WDG, WG, DG)

Dry flowable and water-dispersible granule formulations are much like wettable powders except that the active ingredient is formulated on a large particle (granule) instead of onto a ground powder.

E. Flowable liquid (FL)

Herbicides applied in water bodies as flowable liquids, direct from the container under pressure, without any dilution. These are known as flowable liquid formulations. E.g. acrolein and aromatic solvents.

F. Granules (G)

These are made by loading the toxicant on some dry, inert material, usually attaclay. The herbicide granules vary in size from 0.04 mm to 1.0 mm in diameter. Herbicide granules smaller than 0.04 mm are not used because they drift easily with wind. Eg: Butachlor, 2,4-DEE.

G. Others – Capsules, wax bars, soluble mulches, foam pieces, aerosols etc.