There is often a temptation to apply a double dose of herbicides to a crop when there is left over mixture in the spray tank, simply to avoid waste. However, this innocent action can lead to significant crop damage, especially with herbicides that should only be applied once at low concentrations. In the case of herbicides, more is not always better and caution must always be exercised.
Herbicides are the pivotal element in crop production for combatting weeds and optimising the crop yield. However, their application requires careful attention to the label directions.
Water quality
Water quality significantly affects the efficacy of herbicides. Factors such as the pH, hardness, turbidity and the presence of organic matter can influence how well herbicides perform.
Understanding and managing these factors can help ensure that herbicides are effective in controlling target weeds. Managing the water quality is crucial for the effective use of herbicides. By ensuring the water used for mixing herbicides is within the optimal pH range, has a low hardness and is free from excessive turbidity and organic matter, you can maximise its efficacy and achieve better weed control outcomes.
Regular water testing and the use of appropriate adjuvants and conditioners are essential practices in this regard. Always refer to the herbicide label and manufacturer’s guidelines for specific recommendations on the water quality requirements.
Compatibility
Caution must be exercised when engaging in tank mixing, as certain herbicides may not be compatible. Tank mixing serves to minimise costs by consolidating applications, thereby reducing labour, fuel and wear on spray equipment. Additionally, it optimises favourable spray conditions and can enhance weed control through synergistic effects – wherein certain herbicides boost the performance of others, resulting in superior weed management compared to individual or separate applications.
It’s important to note that some herbicides may be physically or chemically incompatible, rendering them unsuitable for tank mixing. Incompatibility can lead to application challenges, diminished weed control efficacy or even crop damage. Prior to attempting a new mix, it is advisable to seek professional guidance and carefully review the product-specific mixing instructions provided on the label.
Mixing sequence
Mixing agrochemicals, including herbicides, fungicides, insecticides and fertilisers, requires careful attention to ensure compatibility and effectiveness. The correct order of mixing can prevent chemical reactions that may cause clumping, settling or reduced efficacy.
The sequence in which herbicides are mixed is critical to ensure their efficacy and to prevent harmful chemical reactions. Always follow the manufacturer’s instructions regarding the mixing sequence.
Here is the general order of mixing agrochemicals:
Water → water conditioners → wettable powders (WP) and dry flowables (DF) → dispersible granules (DG) or water-dispersible granules (WDG) → flowables (F) or suspension concentrates (SC) → emulsifiable concentrates (EC) → solutions (S) → surfactants, adjuvants and oils → compatibility agents (if needed).
AGITATION
Maintain continuous agitation throughout the mixing and application process. Following this order helps to ensure that the agrochemicals are mixed correctly, preventing issues related to compatibility and efficacy. Always refer to the product labels and manufacturer recommendations for specific mixing instructions and compatibility guidelines.
Adhering to the herbicide dosage
Adhering to the herbicide dosage is crucial for several reasons, all of which contribute to effective weed control, environmental protection and sustainable agricultural practices. Optimal weed control using the recommended dosage ensures that herbicides effectively control target weeds, preventing competition for resources such as water, nutrients and sunlight.
The proper dosage minimises the risk of weed resurgence or resistance development, maintaining long-term weed suppression. Applying the correct dosage also reduces the risk of phytotoxicity or crop damage, which can occur with overdosing. Maintaining the health and vigour of crops is essential for maximising yields and profitability.
Adhering to the herbicide dosage is essential for achieving effective weed control, minimising environmental impacts, preserving biodiversity, managing resistance and ensuring economic efficiency. By following the recommended dosages and integrated pest management principles, farmers can maintain healthy crops, protect the environment and sustainably manage weed populations for long-term agricultural productivity.
Wind speed
The wind speed stands out as one of the most critical factors influencing the spray drift during herbicide applications. Elevated wind speeds can propel droplets away from their intended target area, resulting in off-target deposition and decreased effectiveness.
Prior to spraying, applicators must meticulously assess the wind speed and direction, and make the necessary adjustments to application parameters such as the nozzle selection, spray pressure and angle in order to mitigate drift risks.
Moreover, windy conditions can affect the spray coverage and uniformity, underscoring the importance of precise equipment calibration for optimal herbicide dispersion. By employing drift mitigation strategies and adhering to best practices, applicators can counteract the negative impact of wind on herbicide applications.
It’s worth noting that in windy conditions, the potential for pesticide loss from leaf surfaces and drift distance increases. Smaller droplets in particular tend to drift more due to their slower descent rate compared to larger droplets. While many herbicide labels advise against spraying in wind speeds exceeding 10 km/h or 15 km/h, it’s essential to always consult the specific guidelines provided on the product labels.
Rainfall
Precipitation events, such as rain or dew, play a significant role in determining the effectiveness of herbicide spray tank applications. Rainfall occurring shortly after herbicide application can wash away the herbicide from the target area, reducing its efficacy and potentially requiring reapplication. Conversely, during drought conditions, higher herbicide doses may be necessary to compensate for reduced plant uptake and translocation.
Dew or high moisture levels on plant surfaces can facilitate herbicide absorption, especially for contact herbicides. However, this moisture also heightens the risk of herbicide run-off and environmental contamination.
To optimise weed control outcomes while minimising the environmental impact, it’s crucial for operators to carefully time herbicide applications relative to precipitation events.
Additionally, selecting herbicides with appropriate rain fastness properties or incorporating a sticker adjuvant can help to enhance herbicide retention on target surfaces. This strategic approach can lead to more effective weed management while reducing potential environmental harm.
Time of application and weed/crop condition
The condition of weeds can significantly influence the efficacy of herbicide applications. Several factors come into play:
- Weed growth stage: Herbicides often have specific recommendations for the optimal growth stage of the target weeds. For example, some herbicides may be more effective against young, actively growing weeds, while others may target mature weeds. Applying herbicides at the correct growth stage can maximise efficacy.
- Weed density: The density of weeds in a certain area can impact the herbicide efficacy. Higher weed densities may require higher herbicide rates or more frequent applications to achieve adequate control.
- Weed species: Different weed species have varying levels of susceptibility to herbicides. Some weeds may be more resistant to certain herbicides or may require different treatment methods for effective control.
- Weed health and vigour: Healthy, vigorously growing weeds are generally more susceptible to herbicides compared to stressed or weakened weeds. Factors such as nutrient availability, moisture levels and overall plant health can influence weed susceptibility to herbicides.
- Application timing: Timing plays a crucial role in herbicide efficacy. Applying herbicides when weeds are actively growing and at their most vulnerable stage can improve control. Additionally, proper application techniques, including the spray volume, nozzle selection and application method, can impact the herbicide coverage and uptake by weeds.
Herbicide residual period and crop rotation
The residual period and crop rotation are crucial factors to consider when selecting herbicides, as they can significantly impact both the weed control efficacy and potential crop damage in subsequent seasons.
Crop rotation involves alternating different crops on the same piece of land over time. Certain herbicides may have restrictions or recommendations regarding crop rotation intervals due to their residual activity and potential for crop injury. When selecting herbicides, it’s essential to consider the rotation plans for future crops.
The residual period refers to the duration that a herbicide remains active in the soil after application. Herbicides with longer residual periods can provide extended weed control but may also pose a risk of carryover to subsequent crops.
When selecting herbicides, it’s important to consider the residual period in relation to the planting date of the next crop. Choosing herbicides with shorter residual periods or ones that degrade quickly in the soil may be necessary to minimise the risk of crop injury in subsequent seasons.
Summary
The use of herbicides remains integral to modern crop production, offering effective weed control and optimising yields. However, their application demands meticulous attention to label directions and best practices to avoid unintended consequences.
From avoiding double doses to ensuring proper water quality and adhering to mixing sequences and dosage recommendations, every step in the herbicide application process requires careful consideration.
Additionally, factors such as the wind speed, rainfall and weed/crop conditions further underscore the need for precision and timing in herbicide application. Moreover, understanding the residual period and considering crop rotation plans are crucial for long-term weed management and minimising potential crop damage.
By adhering to these principles and guidelines, farmers can harness the benefits of herbicides while safeguarding crop health, environmental sustainability and longterm agricultural productivity.
Optimise crop yield
Sources
- Brewer International (n.d.). The impact of weather conditions on herbicide spray tank applications. https://brewerint.com/newsinsights/the-impact-of-weather-conditions-on-herbicide-spraytank-applications/ [21 May 2024]
- Department of Primary Industries and Regional Development (n.d.). Factors affecting herbicide performance. Government of Western Australia. https://www.agric.wa.gov.au/grains-research-development/factors-affecting-herbicide-performance?page=0%2C4 [21 May 2024]
- Kriel G & Hanekom L, 2015. Follow these tank mixture guidelines. Grain SA. [21 May 2024]
- Tamil Nadu Agricultural University (n.d.). Herbicide formulation, mixture, adjuvant, application methods and equipment. http://www.eagri.org/eagri50/AGRO304/pdf/lec14.pdf [21 May 2024]
