Formulation of herbicides

In order for the herbicides to obtain a practical value it is necessary to formulate them, that is to say, to fuse them with solvents, diluents and adjuvants, in this way it is possible to create a product called formulation, which is equivalent to its commercial presentation. When speaking of formulation, reference is usually made to the solid, liquid or gaseous form as the chemical is made for application.

Thus, herbicides are brought to the market as formulations, which are presented under a wide variety of trade names, and are sometimes removed as pure chemicals. The formulation is the way in which the pesticide is presented for sale.

One of the main reasons for formulating an herbicide is that the user is allowed an easy, uniform and rapid distribution of the herbicide with a suitable carrier, the water being the carrier most used in most agricultural cases, So that a minimum amount of herbicide can spread evenly over large tracts of soil.

Other justifiable grounds for formulating an herbicide would be to increase or improve the biological activity or effectiveness of the herbicide, to simplify the manipulation of the pesticide by the user (increased safety, reduced risk). In summary, the formulation is made with the intention of optimizing or increasing the properties of a pesticide in all matters concerning its application, effectiveness, handling, safety and storage.

Formulation

From the outset, the herbicides are manufactured in an almost pure state, which is why they are called as a technical grade herbicide. They can be made in solid or liquid state, and it is very seldom suitable to apply it in this way on the crop. The formulated product of each herbicide to be applied with a sprinkler must be soluble or miscible, using a suitable element which in most cases is water. As well as showing good results on the crop, it must also have stability during transportation and storage, being able to withstand various extreme weather situations.

As well as soluble concentrates, water-soluble compounds are formulated in a dispersion of waterdispersed granules, which have finely ground solids in combination with dispersing suspending agents (surfactants, surfactants or adjuvants). These can be applied directly to the sprinkler tank and poured cleanly from the container.

When it comes to compounds with low solubility, the active ingredient can be ground into a dust, fused with an inert carrier and a surfactant to be marketed as a wettable dust (such as simazine). This type of formulation is commonly mixed with very little water, looking for a pasty mixture, before pouring it on the sprinkler tank.

The suspensible concentrates have been able to greatly displace the wettable dust, since the former have an active ingredient which has been finely ground, mixed with surfactants and, in some products, with some non-toxic solvents. That makes this type of formulation achieve a simpler and safer handling in comparison to the manipulation of the wettabledust, in addition it mixes much easier with the water in the tank of the sprinkler.

Active ingredients which are not soluble in water, especially those that are foliar application, could be dissolved in an organic solvent such as xylene, then mixed with surfactants and produce an emulsifiable concentrate. These propagate through the water to give rise to oilyemulsions in water, which are known for their milky appearance.

For reasons of operator safety and environmental impact, synthetic organic solvents are being replaced with emulsifiable concentrates based on vegetable oil and new water based formulas, such as ‘structured surfactant systems’.

Certainly there are a large number of herbicides which are formulated to be used with a water sprayer as a carrier, but there is also, to a lesser extent, a group of active ingredients which are used as dry formulations in the form of granules. These are small particles, almost always with a size of less than 10mm3 and usually have concentrations of active ingredient between 2% and 20%. A tractor-type or rucksack-type pellet applicator is mostly implemented, however, some granulates are ideal for manual dispersion, being useful in small farms, where there is no availability of machinery for the application.

Salts and esters

Different herbicides (such as 2,4-D) are weak acids and react with bases to create salts and with alcohols to produce esters. The salts have solubility in water but not in oil and also have low volatility, while the esters have no water insolubility and if they have oil solubility, also with high volatility.

Esters almost always have anherbicidal activity above the salts, but given their high volatility, it can cause damage to plants outside the space to be treated. Esters of almost all groups of herbicides including aryloxyphenoxyalkanoic acid esters do not have volatility.