Weeds pose a tremendous threat to agriculture as they affect the quality and quantity of agricultural production as well as profit. Asides from reducing agricultural yield in farms, weeds also present fire hazards and may impede work crews in industrial sites. In Nigeria, herbicides have become a widely practised method of removing undesirable plants, proving to be more effective and economical than hand-pulling and hoeing which once held sway as a means of weed control. In this article, we’ll be discussing the types of herbicides in Nigeria. The types of herbicides that would be discussed here are classified according to selectivity, mobility, and timing of application.
The types of herbicides in Nigeria would be discussed below:
-
Types of Herbicides According to Selectivity
The types of herbicides according to their selectivity are selective herbicides and non-selective herbicides.
-
Selective Herbicides
Selective herbicides are formulated to specifically kill kinds of weeds that pose harm to the desired plants on the farm without harming the crop plants or pasture. To achieve effective weed management with selective herbicides, they should be applied at the prescribed application rate, either through weed foliage or soil containing weed seeds or seedlings. Since selective herbicides are designed to control specific weeds, for example, broadleaf weeds or grasses, it is important that you read the product label of the herbicide to be sure of the exact type of weeds it is designed to eliminate. Examples of selective herbicides you can find in Nigeria include but are not limited to,
-
Non-Selective Herbicides
Unlike selective herbicides that are designed to kill specific types of undesirable plants, non-selective herbicides are formulated to control a broad spectrum of weeds both grasses and broadleaf weeds. The purpose of non-selective herbicides is therefore to kill all vegetation, whether by contact or systemic mode of action. This type of herbicide can be applied to weed foliage or soil containing weed seeds or seedlings, however, it’s best to apply non-selective herbicides to weed foliage to achieve effective weed control. In Nigeria, the non-selective herbicides in the market have paraquat or glyphosate as active ingredients. Some examples of non-selective herbicides in
Nigeria includes paraquat and glyphosate.
-
Types of Herbicides According to Mobility
The herbicides categorized according to mobility are contact herbicides and translocated herbicides.
-
Contact Herbicides
Contact herbicides are formulated to eliminate all the plant parts onto whose surfaces the chemical is applied. This type of herbicide has limited movement within the undesirable plant it’s applied to, so the targeted weed must be completely covered with contact materials during application to achieve effective weed control. Contact herbicides are most effective against annual weeds. This type of herbicide usually produces rapid results, as fast as 24 hours after application of the chemical on the weed parts. Examples of contact herbicides in Nigeria include paraquat, oxyfluorfen, diquat, and bromoxynil.
-
Translocated Herbicides
Translocated herbicides work by circulating the chemical absorbed by the roots or foliage of the targeted weed plants to distant tissues within the plant system through the xylem and phloem. When using translocated herbicides for weed control, it takes about two weeks or thereabout for the targeted undesirable plants to begin to develop symptoms of rot. This type of herbicide may be effective in eliminating all kinds of weeds but are most effective against perennial weeds. To experience effective weed control with translocated herbicides, it is essential to uniformly apply the chemical on the target undesirable plants.
-
Types of Herbicides According to Timing of Application
There are three categories of herbicides according to the timing of application. They include pre-planting herbicides, pre-emergence herbicides and post-emergence herbicides.
-
Pre Planting Herbicides
Pre-planting herbicides are formulated to control weeds on a planting field before the crop is planted. This type of herbicide is effective against annual weeds and is usually applied a few days to weeks of planting. To achieve effective weed control with pre-planting herbicides, it is important to read the label to note the types of target weeds and the recommended rate, as well as perform the herbicide application when the grasses or broadleaf weeds are young and thriving as the effect of pre-plant herbicides on mature weeds are not so effective. So, In the case where the weeds are already tall and mature, you should mow first and return to spray the chemicals in a few days, even if the new regrowth is minimal. Examples of pre-planting herbicides in Nigeria include Paraforce(paraquat), and Metaforce (S-Metolachor).
-
Preemergence Herbicides
Pre-emergence herbicides are used after crop planting has been done, but before crops and/or weeds emerge through the soil surface. This type of herbicide is also referred to as residual herbicide. Preemergence herbicides control weeds by root, shoot and seed absorption. The application of pre-emergence herbicides immediately after planting are proven to provide weed control, especially when weather or busy schedules make it difficult for a timely postemergence herbicide application when the crops and weeds emerge through the soil surface.
Before the application of any pre-emergence herbicide, it is important to know the following: weed spectrum, length of residual activity, modes of action, application timing flexibility and crop rotation flexibility. Some pre-emergence herbicides in Nigeria include Forestop (Pendementhalin) and Butaforce (Butachlor).
-
Postemergence Herbicides
Post-emergence herbicides are specifically designed to attack weeds after they might have emerged through the soil surface. They provide control against existing weeds on the farm and can also help prevent future ones. Post-emergence herbicides may attack the foliage of the weed or flow systemically through the roots of the weed, depending on if the herbicide is in contact or translocated material. Post-emergence herbicides may also be selective or non-selective and may come in the form of spray-on formulas or granular applications.
Post-emergence herbicides are best applied on rainless days, after which the chemicals would be left to dry for eight hours or so, before being watered. Before using any post-emergence herbicide, consider the rate of application, residual action, and the target weeds of the chemical. Examples of post-emergence herbicides include Aminoforce, Basagran, and Diuron.