Understanding Pre-Emergent Herbicides: Balancing Environmental Protection and Performance

Vegetation managers responsible for roadsides, rail corridors, utility networks, substations, airports, industrial sites and other critical infrastructure face a growing range of challenges. One important consideration is understanding how a herbicide will behave after application and whether it is suitable for the site being managed.

All herbicides go through a rigorous registration process regulated by the Australian Pesticides and Veterinary Medicines Authority (APVMA). As part of this assessment, potential risks to the environment are considered. The product label then sets out how the herbicide must be used to manage these risks.

When assessing a herbicide, a useful starting point is to check the product label for guidance on:

• Spray nozzles and droplet sizes
• Buffer zones
• Protection of native plants
• Spray application weather condition restraints
• Soil moisture conditions 
• Water application rates

Labels that include this information have been assessed and registered by the APVMA. Following the label directions is an important part of ensuring the herbicide is used safely, effectively and in accordance with its registration

Understanding key herbicide characteristics
Pre-emergent, or residual, herbicides are becoming increasingly important tools for effective and economical control of unwanted vegetation. Rather than simply controlling weeds that are already present, they prevent weeds from establishing after application. Differences in how these herbicides behave in the environment can be better understood by looking at several key measurable characteristics.

Volatilisation
Herbicides can be classified as volatile or non-volatile. Volatilisation occurs when a herbicide changes from a liquid to a gas after application. Once in gas form, the herbicide can move away from the treated area and potentially cause off-target damage.

Binding
Herbicides that bind tightly to soil and organic matter are less likely to move from where they are applied, unless the soil itself moves. Tight binding is an important characteristic for pre-emergent herbicides. Where binding is weak, there is greater potential for the herbicide to move during rainfall and cause off-target damage.

Persistence
Persistence refers to how long a herbicide remains active in the soil. A herbicide with a longer half-life generally remains active for longer, providing longer-term weed control.

Solubility
Solubility refers to how easily a herbicide dissolves in water. Herbicides with high solubility have greater potential to move through the soil with water, which can increase the risk of off-target damage to surrounding vegetation or aquatic areas.

Together, these characteristics help determine where a pre-emergent herbicide sits in the soil, how it moves and how long it remains active – all important considerations when selecting a product for long-term vegetation management.

Applying these principles in practice
Looking at these characteristics together can help vegetation managers understand how a product is likely to behave in a particular environment.

This is where Esplanade^® Herbicide stands out. It is non-volatile, has low solubility and binds well in the soil where germinating weed seeds sit. When applied according to label directions, these characteristics can help minimise the potential for off-target movement. The label also provides detailed directions covering areas such as spray nozzles, application conditions, water rates and buffer zones.

Esplanade is registered for pre- and post-planting weed control in certain forestry plantations, including nominated tolerant species. Before application, always refer to the Tolerant Species table and Directions for Use on the product label to confirm the situations and species relevant to your site.

As a broad-spectrum residual herbicide, Esplanade controls weeds before they establish. By preventing new weeds from emerging, maturing and producing seed, an effective residual program can help reduce replenishment of the soil seed bank over time. For vegetation managers, this can mean fewer weeds establishing between treatments and less time spent repeatedly managing new growth.

Supporting resistance management 
Esplanade introduces an alternative mode of action for many traditional vegetation management programs. Incorporating different modes of action into weed control programs is a key principle of resistance management, helping reduce reliance on existing chemistry and supporting the long-term sustainability of herbicide tools.

Partnering for better outcomes
Effective vegetation management is more than choosing a herbicide. It requires the right product, applied in the right situation, as part of a well-planned long-term vegetation management program.

Drawing on expertise in herbicide technology and integrated vegetation management (IVM), Envu works closely with vegetation managers to address changing operational requirements, regulatory considerations and asset management objectives.

Whether reviewing existing vegetation management practices, identifying opportunities to improve maintenance programs, or considering the longer-term economic impact of vegetation control decisions, Envu is committed to sharing knowledge and helping organisations achieve effective, sustainable vegetation management outcomes.