Herbicide classification and usein agriculture


An herbicide is a phytosanitary product used to kill undesired plants.If an herbicidekills only certain target plants while being relatively harmless to the desirable plants, it is called a selective herbicide; many interfere with weed growth because they are based on hormones presentin target plants. Othernon-selective herbicides are made for clearing big areas indiscriminately; they kill the whole plant that they come into contact with.

The active ingredients in herbicides are chemicals that can kill or suppress growth in certain unwanted plants. We know these plants as weeds,which consist of any vegetativematter that develops in a particular area and is capable of interfering with the development of other desired vegetation.

Herbicides, as well as other pesticides, are tested and recommended specifically for certain uses. This means that any given product is suitable for certain crops that tolerate it well, and for certain weed species that are susceptible to elimination by that herbicide.

Herbicide classification

Selective herbicides: These act on certain plants belonging to a given botanical family, and do not exert control over other plants belonging to other botanical families. For example: 2,4-D acts on weeds with broad leaves (dicots) and does not affect narrow leaves (grasses), Chlorimuron ethyl (brand name: Classic) controls broadleaf weed species present in the cultivation of soybeans, for example, without affecting the cropitself.

Non-selective or total herbicides: These control all kinds of plant matter, acting on any species of vegetation; they are, therefore, non-selective. For example: Glyphosate (brand name: Round Up) for the control of thin leaves and some broad leaves or 2,4-D for control of broadleaf weeds, do not present selectivity for any weed or crop.

Herbicides by mode of action againstweeds

  • Contact herbicides(Click Here): These herbicides act only in the places that have been covered by the product;thus, it is important to thoroughly coat the weeds that need to be controlled. The roots are not affected by these herbicides and can reappear. For example, Paraquat (Gramoxone), Lactofen (Charges), Bentazon (Basagran).
  • Systemic herbicides or internal action herbicides: Once applied on the weeds or surrounding soil, they are absorbed and destroy all the organs of the plant, including the roots. For example, 2,4-D, Glyphosate (Round Up), Sethoxydim(Poast), Clethodim(Select).

By the moment in which they are applied

  • Pre-seed Herbicides: These are applied before the sowing or planting of the crop to eliminate existing weeds. For example, Sulfamethazine (Boral SC).
  • Pre-emergent Herbicides: The application of these herbicides is done after sowing the crop, but before the germination of the crop and/or the weed. They destroy small weed plants after they germinate. For example, Imazaquin (Scepter), Flumetsulam (Presides), Pendimethalin (Herbadox).
  • Post-emergent Herbicides: These are applied after crop and weed germination; it is recommended to do it when the weed is in its initial stages of development. The ideal application time is whennarrow leaved speciesgrowinto clusters, andwhen broad leaved species have up to 4 real leaves. The affected crop can have late application when more developed weed growth is detected.

Herbicide application in agriculture

Whatever the herbicide’s mode of action or application window, there will be control of the existing susceptiblespecies in an area determined before sowing, or in a crop that is suffering from competition for resources.

For any herbicide to be applied, growers need to havesubstantial technical knowledge and respect for certain established rules, suchmixing procedure,environmental factors, timing and application technology, as well as the size of the weeds. For example, some herbicides can be used in conjunction with another type of herbicide with no negative effects; in other cases, this could cause a dangerous chemical interaction.

The practice of applying herbicides is most effective when combined with other strategies for weed management and prevention of weed resistance to herbicides. However, herbicides will continue to play an important role in agriculture for many years to come.

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