Effective weed management is an integral part of successful farming. If weeds are not properly managed, they consume nutrients, sunlight, and water, thereby reducing crop quality and yield.
Selecting the correct herbicide is crucial. The first step to a better decision is to know the difference between pre-emergent herbicides and post-emergent herbicides.
Therefore, the central focus of this blog will be on a concept, pre-emergent vs post-emergent herbicides. Both types have different timings in terms of application and must be synchronized with your crop stages.
Weed Management and the Role of Herbicides
Weeds can reduce productivity and spike the farm costs. Manual removal is indeed slow, and traditional methods are now not enough.
Today, farmers use herbicides to achieve effective weed control as part of modern farming solutions. These chemical solutions are either applied before the weeds emerge or after they sprout.
That is precisely why you should have a clear understanding of the differences between pre-emergent and post-emergent herbicides. You can reduce your labor needs, ensure a healthy harvest, and protect your fields by applying these herbicides at the right time.
What Are Pre-Emergent and Post-Emergent Herbicides?
As the name suggests, pre-emergent herbicides are chemicals that you add to the soil before the weeds sprout. They form a sort of protective barrier that prevents weed germination. These types of herbicides do not kill the existing weeds, but they stop new ones from emerging.
Experienced farmers use them after the sowing stage, especially during the Kharif season (monsoonal crop) and Rabi season (winter crop), to prevent early weed competition.
On the other hand, post-emergent herbicides are used for the stage where weeds have already emerged from the soil. They are designed to target the already existing weeds throughout the stage of commercial crop growth.
They either work topically upon contact with the weed’s surface (contact herbicides) or act from within the plant after getting absorbed (systemic herbicides).
By understanding the timing and method of application for each, you can reduce unnecessary spray sessions and save time and money. Choosing from pre-emergent vs post-emergent herbicides entirely depends on your crop stage, the soil’s history, and the types of weeds you encounter.
Understanding the functions of both types can also support better weed control timing. Weed control timing is a critical factor that significantly influences the survival of your commercial crop.
When and Where to Use Each Type in Indian Crops
Indian cropping patterns vary by region. Therefore, your herbicide applications may also vary based on the same factor. The field’s condition and timing play crucial roles in a decision as important as pre-emergent vs post-emergent herbicides. Furthermore, here’s a detailed breakdown of the usage of both herbicide types, along with examples.
Pre-Emergent Use in Crops
Use the pre-emergent herbicides after sowing, but also before the first weeds can sprout. Pre-emergents need a moist soil for activation. Hence, they are more effective in monsoons, right after rainfall, and in irrigated fields.
Use cases:
- Wheat (Rabi Season): Farmers in northern Indian states often use pre-emergents within 2 to 3 days of sowing. This step is highly productive, as it prevents the growth of broadleaf weeds and annual grasses before they appear. Pendimethalin 38.7% CS + Metribuzin 70% WP makes an excellent pre-emergent for wheat production.
- Paddy (Kharif Season): In paddy fields with an existing crop, pre-emergents can effectively prevent weeds like Echinochloa, also known as barnyard grass. It acts to prevent the germination of weeds during the first 20 days.
- Maize and Cotton: These crops can greatly benefit from pre-emergent spraying, right after the sowing stage, when the seed is still establishing its roots.
The benefits of pre-emergents:
- Early eradication of weeds
- Reduced resource competition
- Fewer sprays in the long term
Maintain or refer to a herbicide usage guide that provides information based on tillage practices, soil moisture, and crop sensitivity. These factors establish a clear distinction in the concept of pre-emergent vs post-emergent herbicides.
Post-Emergent Use During Crop Growth Stages
Use the post-emergent herbicides after the weeds are visible in the field. They are more suitable when you want to control grassy weeds or broadleaf weeds after they have germinated.
Use cases:
- Soybeans and Pulses: Post-emergents assist us in tackling the late-emerging weeds during the growth stages. A combination of Clodinafop-propargyl 15% WP + Metsulfuron-methyl 1% WP has been known as a great post-emergent herbicide mixture when growing soybeans and other pulses.
- Sugarcane: Weeds such as Cynodon and Cyperus can be effectively controlled with post-emergent herbicides, applied 30 to 45 days after sowing.
- Vegetables (Brinjal, Tomato): For these, precision is the key. Use low-dose post-emergents that do not harm the crop foliage.
Timing matters when dealing with post-emergents. Late application or spraying during sensitive flowering stages can harm yields.
To put it simply, having a perspective on pre-emergent vs. post-emergent herbicides and thinking that you need only one of the two is incorrect. They are both equally essential and can indeed go hand in hand.
Choosing the Right Herbicide Based on Crop Stage and Weed Type
Herbicide application isn't just about killing the weeds. It is much more than just that. The three aspects that matter a lot in weed management are the when, the where, and the how.
When to apply, where to use it precisely, and how the weeds interact with your specific crop during its growth stages, the herbicide choice should always be made while considering two key factors: the crop stage and weed biology.
1. Start with the crop’s growth stage
The growth stage of your crop determines its sensitivity to chemical interference.
- Pre-emergent herbicides can be used before your crop or weeds germinate. They are the best solution for land preparation or right after sowing. For example, applying a pre-emergent in rabi crops like mustard or wheat helps in early root development.
- On the other hand, post-emergent herbicides are applied when weeds are already visible and competing for resources. For crops like maize and cotton, post-emergents are most effective during mid-season weed development.
But one thing to always remember is that the timing errors can lead to crop injury or improper weed management. Using a post-emergent herbicide too early or too late can lead to wasted money and lower yields. Hence, instead of trying to choose between pre-emergent vs post-emergent herbicides, you can use both to your advantage.
2. Know the type of weed you are targeting
Weeds differ in their life cycles, resistance patterns, and physical attributes, such as leaf shape and height. They are mainly categorized as:
- Broadleaf Weeds - Chenopodium aka bathua
- Grass-type Weeds - Echinochloa aka sawan
- Sedges - Cyperus aka motha
Dealing with broadleaf weeds may require different herbicides than those used for grasses, even when they coexist in the same crop field.
These weed types can be targeted using selective herbicides, which also protect the crop. Thoroughly examining and surveying the weeds, along with their locations, can also improve herbicide efficiency.
3. Understand the weed growth timings
Some weeds grow alongside the crop. Others emerge weeks later, in the commercial crop’s growth stage. This is exactly why weed control timing matters. The first wave requires pre-emergents, and the regrowth, along with late bloomer weeds, need post-emergents for efficient control.
A sequential strategy ensures longer control in high weed pressure areas. Basically, a planned sequence of pre-emergents followed by post-emergents. The fact that both types have their own benefits undermines the argument between pre-emergent and post-emergent herbicides. They can both benefit you with properly planned weed management.
4. Think about long-term effects: Resistance and Soil Health.
Repeated use of the same chemicals on the same piece of land creates stubborn and resistant weeds that do not respond to your weed management plans. Wherever possible, you should rotate the herbicide groups and use proper dosages. You can also combine manual or mechanical weeding with these techniques.
To understand more about incorporating manual methods, here’s an ICAR-Pantnagar research study that shows Pendimethalin 1 kg/ha + hand weeding in Indian mustard increased yield by 22%.
Not all herbicides are safe for your specific regions or specific crop. Therefore, check the label and the crop-specific guidelines before every use.
Calibrate and maintain the sprayers properly, and always consider the weather conditions. Especially in monsoon (kharif), as there is a high risk of dilution or the herbicides getting washed off.
Be A Partner
