Question

The herbicides applied after the emergence of weeds and crops are called as _________.

• A. Post-emergence herbicides
• B. Pre-emergence herbicides
• C. Pre-plant herbicides
• D. Pre-harvest herbicides

Hint:

Herbicide Application Timing:
1. Before Sowing: Pre-plant incorporation (PPI).
2. After Sowing, Before Germination: Pre-emergence (PRE).
3. After Crop/Weed Germination: Post-emergence (POST).

Answer 1

The Correct Option is A

Concept:
In weed science and chemical weed management, herbicides are systematically classified based on their time and method of application relative to the crop and weed growth stages.
The timing of chemical delivery determines whether the herbicide acts primarily through root uptake from soil or foliar absorption through weed leaves.
Selecting the proper application window ensures selective weed control while avoiding phytotoxic injury to the establishing main crop.
Understanding standard operational terminology is critical for field agronomy.

Step 1: Defining Time of Application Classes:
- Pre-plant incorporation (PPI): Applied and mixed into the soil before the crop is sown (e.g., Fluchloralin).
- Pre-emergence (PRE): Applied to the soil surface after sowing the crop seeds but before the crop and weed seedlings emerge above the ground (e.g., Pendimethalin, Atrazine).
- Post-emergence (POST): Applied directly onto the foliage after both the crop and weeds (or only the weeds) have emerged from the soil surface.
- Pre-harvest: Applied just before crop harvest as a desiccant or defoliant to facilitate mechanical harvesting.

Step 2: Identifying the Defined Term:
The question describes herbicides that are sprayed or applied after the emergence of both weeds and crops.
By standard agronomic definition, these chemicals are termed Post-emergence herbicides (e.g., 2,4-D, Sulfosulfuron, Clodinafop-propargyl).

Step 3: Final Answer:
Therefore, the herbicides applied after emergence are known as Post-emergence herbicides, matching option (A).