🗂 Herbicide Classification, Formulations, and Methods of Application
Learn how herbicides are classified by selectivity, mobility, timing, chemistry, and formulation, and how application methods affect performance.
This lesson organizes herbicides into practical categories so that selection and application become technically meaningful rather than memorized by name alone.
Why Herbicide Classification Matters
Herbicides differ in:
- where they act
- how they move
- which weeds they control
- which crops tolerate them
- when they should be applied
Classification helps the agronomist choose the right herbicide for the right situation.
1. Classification Based on Target Site of Application
Soil-applied herbicides
These act mainly through roots or underground parts after placement in the soil.
Example:
- fluchloralin
Foliar-applied herbicides
These are sprayed on plant foliage and act through leaf absorption.
Examples:
- glyphosate
- paraquat
2. Classification Based on Selectivity
Selective herbicides
These control certain weeds without seriously injuring the crop when used correctly.
Example:
- atrazine in tolerant crops
Non-selective herbicides
These injure or kill most vegetation they contact.
Examples:
- paraquat
- glyphosate
3. Classification Based on Mobility in Plant
Contact herbicides
These kill only the plant parts with which they come in contact.
Example:
- paraquat
Translocated or systemic herbicides
These move from treated parts to untreated plant tissues through xylem, phloem, or both.
Example:
- glyphosate
4. Classification Based on Time of Application
Pre-plant application
Applied before sowing or planting.
Pre-plant incorporation
Applied before planting and mixed into the soil. This is important for volatile or light-sensitive herbicides.
Pre-emergence application
Applied after sowing but before emergence of crop or weeds, depending on the context.
Early post-emergence application
Applied soon after weed emergence at very early growth stages.
Post-emergence application
Applied after weeds or crop have emerged.
5. Classification Based on Chemical Nature
Herbicides may be grouped by chemical family, such as:
- phenoxy acids
- triazines
- dinitroanilines
- ureas
- amides
- bipyridyliums
- glycine derivatives
This grouping becomes important when studying:
- mode of action
- selectivity
- persistence
- resistance management
6. Formulations of Herbicides
Commercial herbicides are supplied in different formulations so they can be stored, diluted, handled, and applied effectively.
Common formulations include:
- EC: emulsifiable concentrate
- WP: wettable powder
- WDG or granules
- SC: suspension concentrate
- soluble salts
The formulation affects:
- ease of mixing
- spray behavior
- safety
- field convenience
7. Methods of Herbicide Application
Soil application methods
- surface application
- subsurface placement
- band application
- fumigation
- herbigation
Foliar application methods
- blanket spray
- directed spray
- protected spray
- spot treatment
Factors Affecting Method Selection
Method of application depends on:
- crop spacing
- weed spectrum
- herbicide selectivity
- soil texture
- moisture condition
- labour and equipment availability
- economics
Management Implication
Correct classification is not just theory. It determines:
- which herbicide to choose
- how to apply it
- when to apply it
- how to avoid crop injury and poor control
Summary Cheat Sheet
- Herbicides are classified by target site, selectivity, mobility, timing, and chemical family.
- Soil-applied and foliar-applied herbicides behave differently and must be used accordingly.
- Selective herbicides are crop-safe only when matched properly to crop, weed, and dose.
- Formulation affects handling and application efficiency.
- Method and timing of application are as important as herbicide choice itself.
References
1 source • [1]
References
AGRO304 lecture handout
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