💨 Low-Volume Herbicide Application, Adjuvants, and Dose Effects

This lesson explains how application technology affects herbicide performance and why dose quality matters just as much as herbicide choice.

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What Is Low-Volume Herbicide Application?

Low-volume application means using a smaller spray volume while still delivering the required amount of herbicide to the target weeds.

This approach is useful when:

• target weeds are clearly identifiable
• good spray coverage can still be achieved
• labour and transport efficiency matter

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Advantages of Low-Volume Application

• lower carrier volume
• easier field handling
• reduced application cost in some situations
• less unnecessary wetting of non-target area
• more targeted delivery when done properly

Limitations

• coverage failure if droplets are poorly distributed
• high dependence on sprayer calibration
• greater risk of dose variation if operator technique is poor

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Herbicide Mixtures

Herbicide mixtures involve combining two or more herbicides for broader or more dependable weed control.

Why mixtures are used

• broaden spectrum of control
• improve effectiveness in mixed weed flora
• reduce dependence on one active ingredient
• sometimes lower dose of each component

Types of mixtures

• tank mixtures prepared before spraying
• ready-mix products supplied by manufacturers

Mixtures are useful only when technically compatible and agronomically justified.

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Herbicide Rotation

Herbicide rotation means using different herbicides or different modes of action in sequence over seasons or crops.

Why rotation matters

• reduces risk of resistance buildup
• helps control weed-flora shift
• lowers repeated selection pressure from one molecule

Rotation should be planned by active ingredient or mode of action, not just by trade name.

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Herbicide Tolerance and Resistance

Tolerance

Tolerance is the natural ability of a plant species to survive a herbicide dose that would injure another species.

Resistance

Resistance is the inherited ability of a weed biotype to survive a herbicide treatment that once controlled it effectively.

This difference is important:

• tolerance is natural species behavior
• resistance develops or is selected within a population

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Effect of Sublethal Dose

Sublethal dose means a dose too low to kill the weed effectively.

This may happen because of:

• underdosing
• uneven spray
• wrong calibration
• drift loss
• dense crop canopy blocking coverage

Problems caused by sublethal dose

• survival of partially affected weeds
• regrowth
• poor control impression
• stronger selection for resistance

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Adjuvants in Herbicide Application

Adjuvants are materials added to improve herbicide application or activity.

Their functions may include:

• better spreading
• improved sticking
• increased penetration
• reduced evaporation
• buffering spray water
• reducing drift

Examples of adjuvant roles:

• surfactants
• stickers
• spreaders
• wetting agents
• drift control agents

Adjuvants do not replace the herbicide. They improve how the herbicide performs under field conditions.

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Managing Herbicide Residues in Soil

Residual herbicide hazard can be reduced by good management such as:

• using optimum dose
• crop rotation
• use of organic manures
• ploughing or dilution through cultivation
• leaching where appropriate
• use of safeners or activated carbon in special cases

This is especially important in intensive cropping systems with sensitive succeeding crops.

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Management Implication

Effective herbicide use depends on:

• correct dose
• correct calibration
• correct spray volume
• suitable adjuvant where required
• resistance prevention through rotation and integration

Poor application technology can make a good herbicide fail.

Summary Cheat Sheet

• Low-volume application uses less carrier volume but demands accurate calibration and good coverage.
• Herbicide mixtures broaden control, while herbicide rotation helps reduce resistance pressure.
• Tolerance is natural survival ability; resistance is inherited survival after repeated selection.
• Sublethal doses encourage weed survival and resistance development.
• Adjuvants improve herbicide performance by affecting spread, sticking, penetration, and drift behavior.

References

1 source • [1]

[1]

AGRO304 lecture handout