Common Herbicide Application Mistakes: What Went Wrong?

 Herbicides are a crucial component of weed control in modern agriculture.

When applied correctly, herbicides help farmers protect their crops, improve yields and reduce competition from unwanted weeds. However, mistakes during herbicide application can lead to reduced efficacy, crop damage, increased costs and long-term weed resistance.

1. Incorrect Herbicide Selection

Using the wrong herbicide for a specific weed species or crop is a fundamental mistake that can render an application ineffective. Broadleaf weeds, for instance, require broadleaf  herbicide or non-selective herbicide for effective control. .

Consequences

• Poor weed control, leading to increased weed competition.
• Potential damage to the crop if the wrong herbicide is applied.
• Wasted time and resources on ineffective treatments.

How to Avoid It

• Properly identify the weed species present in your fields before selecting a herbicide. Tools such as field scouting apps or weed identification guides can assist in accurate identification.
• Match the herbicide to both the crop and the weeds it is designed to target. Always read the product label before application.

2. Application Timing Errors

Applying herbicides at the wrong time—either too early or too late in the growth stage of weeds—can drastically reduce their effectiveness. 

Consequences

• Reduced efficacy as weeds become less susceptible to the herbicide.
• Increased weed competition, resulting in lower crop yields.
• Higher costs if reapplication is required.

How to Avoid It

• For pre-emergent soil active herbicides, ensure timely application before weed germination occurs.
• For pre-seed  burndown and in in-crop herbicides, apply when weeds are small and actively growing.
• Monitor weed growth stages through regular field scouting and align applications with weather conditions to avoid delays.

3. Improper Spray Coverage

Inadequate spray coverage is one of the most common application mistakes. Poor coverage often results from insufficient water volume, incorrect nozzle choice or uneven distribution of the spray solution. This is particularly problematic for contact herbicides that rely on thorough coverage for efficacy.

Consequences

• Incomplete weed control, leaving patches of weeds to compete with crops.
• Potential for weed escapes, which can spread and increase long-term weed pressure.
• Wasted herbicide, leading to unnecessary costs.

How to Avoid It

• Use the correct nozzle type for the herbicide being applied. Flat fan nozzles are ideal for contact herbicides, while coarse drift-reducing nozzles may be better for soil active products.
• Maintain proper boom height and travel speed to achieve uniform coverage across the field.
• Increase water volume when applying herbicides that require thorough coverage, particularly when targeting dense weed populations.

4. Spray Drift and Volatilization

Spray drift occurs when herbicide droplets are carried by wind to unintended areas, while volatilization happens when herbicides evaporate and move as a vapor. Both can result in herbicides reaching non-target crops, water sources or natural habitats.

Consequences

• Crop damage in neighbouring fields, which may result in financial losse.
• Environmental contamination, potentially affecting water quality and wildlife.
• Reduced efficacy in the target field as the herbicide does not reach its intended location.

How to Avoid It

• Monitor weather conditions before and during application. Avoid spraying during windy conditions (wind speeds above 15 km/h) or when temperature inversions are present.
• Use drift-reducing nozzles and lower spray pressures to produce larger droplets that are less likely to drift.
• Choose herbicides with low volatility when spraying near sensitive crops or areas, and ensure you are keeping your sprayer speed down.

5. Tank Mix Compatibility Issues

Mixing incompatible herbicides or adding other chemicals, such as fertilizers or insecticides, can result in tank mix failure. Physical incompatibility may cause herbicides to clump, settle or clog the sprayer, while chemical incompatibility may reduce efficacy through antagonism.

Consequences

• Loss of herbicide activity, resulting in poor weed control.
• Equipment damage due to clogged nozzles or lines.
• Additional costs to clean equipment and repeat applications.

How to Avoid It

• Always perform a jar test before mixing products to confirm compatibility.
• Follow the herbicide label for proper mixing order. A general rule is to add products in the  WAMLEGS sequence: Wettable powders, agitate, microcapsule suspension, liquid flowables, emulsifiable concentrates, glyphosate and surfactants.
• Use clean water and ensure your water is tested, as too hard or soft of water can interact negatively with herbicides

6. Neglecting Calibration of Equipment

Improper calibration of sprayers can lead to under-application or over-application of herbicides. Both errors compromise weed control and may cause unintended crop damage or environmental harm.

Consequences

• Under-application reduces weed control, leading to resistance and yield loss.
• Over-application can cause crop injury, increase herbicide costs, and harm the environment.
• Inefficient use of the product, increases labour and operational costs.

How to Avoid It

• Regularly calibrate sprayers to ensure accurate application rates and even distribution.
• Check nozzle flow rates and replace any worn or damaged nozzles.
• Adjust ground speed and boom height to match field conditions and product requirements.

7. Ignoring Resistance Management

Repeated use of the same herbicide mode of action (MOA) can accelerate weed resistance. When resistance develops, weeds are no longer controlled by specific herbicides, reducing options for future management.

Consequences

• Increased weed pressure, as resistant weeds spread rapidly.
• Higher costs to control resistant populations with alternative or more expensive herbicides.
• Limited herbicide options for long-term weed management.

How to Avoid It

• Rotate herbicides with different modes of action to reduce selection pressure on weed populations.
• Incorporate cultural practices such as crop rotation, tillage, and cover crops to suppress weeds.
• Use tank mixes with multiple effective modes of action to delay resistance development.

Mistakes during herbicide application are costly, both in terms of crop yield and long-term weed management. By selecting the right herbicide, ensuring proper application timing, and calibrating equipment, farmers can improve the efficacy of their broadleaf herbicides and other crop protection products.

Attention to detail will help protect yields and maintain effective weed control strategies for years to come. Learning from these common mistakes and implementing best practices will set the foundation for successful and sustainable herbicide application.