A field without crops ready for pre-emergence herbicide applications to place before crops emerge. Proper application helps provide a good competition-free environment for crops to begin their development.

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Pre-Emergence Herbicide Applications

Steve Doench, Head of Sustainable Agronomy
Steve Doench, Head of Sustainable Agronomy

Planting season is underway, and despite the recent cooldown, lots of planting activity will be taking place now through May. Pre-emergence herbicide applications will be taking place soon before crops emerge, and proper application helps provide a good competition-free environment for crops to begin their development.

Important considerations for pre-emerge herbicides are:

    • Ensuring planned post applications have a different mode of actions to prevent weed resistance.
    • Allowing for any planned cover crops or rotational crops to avoid carryover effects.
    • Be mindful of cool weather conditions that can increase the chances of crop injury after application.
    • Good application timing is crucial as precipitation is needed to activate most soil-applied herbicides to control emerging weeds.

Pre-emergence herbicide applications often incorporate several active ingredients in a tank mix and may include a liquid fertilizer component. Because of the complexity of chemicals in a spray tank, it is good to make sure that the blend is compatible . Read and follow all label directions to make sure each product can be mixed and applied. Knowing whether tank mix ingredients work together can be done with a simple jar test to see how each product reacts when mixed. If a jar test is successful and follows the label directions, there still can be additional instructions to follow based on labels for the products in the tank mixture. So be informed about all requirements for all tank-mix partners.

Bottle on the leftBottle on the left is a tank mix without compatibility agent; the bottle on the right is the same tank mix with Exacto compatibility agent is a tankmix without compatability agent; the bottle on the right is the same tank mix with Exacto compatibility agent
Bottle on the left is a tank mix without compatibility agent; the bottle on the right is the same tank mix with Exacto compatibility agent.

The images above show a tank mix with various tank-mix ingredients and an Exacto compatibility agent, while the images on the right are the same tank-mix partners without a compatibility agent. The tank mix without the compatibility agent shows coagulation which might cause clogging and hinder the deposition of the active ingredient. Cleaning afterwards will be more difficult for the tank mix without the compatibility agent as well.

When filling tank mixes, it is vital to start with a spray tank at least half full of the carrier and then add products in a sequence that mixes best. Also, here labels provide the correct instructions but are often following the W-A-L-ES plan.

The W-A-L-E-S plan consists of the five following steps:

1. Wettable Powders (WP) then Flowables (F, DF)
2. Agitate then add anti-foaming compounds or buffers.
3. Liquid and Soluble products
4. Emulsifiable concentrates (EC)
5. Adjuvants

In these steps, dry ingredients are added first, followed by liquids, emulsifiable concentrates, and oil-based products.

Before and after adding the various products, proper agitation is required, and it is best to apply shortly after mixing.

For complex tank mixes, and if the product labels allow their use, compatibility agents and defoamers can add a lot of functionality to ensure herbicides are not adversely affected by pH, minerals (hard water), and fertilizers. Adding chemicals with different preferred environments can result in tank mixes that cause a lot of problems:
    • The chemicals separate out.
    • Clogged spray lines and nozzles.
    • Loose effectiveness during application.
    • Difficult to clean out.

Soil deposition aids adjuvants can help improve soil surface coverage and increase soil adsorption while reducing the runoff potential of soil-applied herbicides. They can also increase soil contact and slow evaporation to increase the amount of pesticide on the target and how long the herbicide can be active.

The Exacto Soil Deposition Aid Adjuvant significantly improved Palmer amaranth control with Balance Flexx (BF; 4 oz/ac) compared to the herbicide alone.
The Exacto Soil Deposition Aid Adjuvant significantly improved Palmer amaranth control with Balance Flexx (BF; 4 oz/ac) compared to the herbicide alone.

This is crucial to get optimal efficacy for herbicides that can interact with and control newly emerging weeds.

Finally, consider using a good tank cleaner to ensure that the tank is clean and ready to go for applications further in the season and there will be no accidental contamination.

Removal of herbicide compounds (glyphosate + dicamba or glyphosate + fomesafen) from tank surfaces with and without tank cleaners. Herbicide concentrations quantified by HPLC-MS.
Removal of herbicide compounds (glyphosate + dicamba or glyphosate + fomesafen) from tank surfaces with and without tank cleaners. Herbicide concentrations quantified by HPLC-MS.
A field without crops ready for pre-emergence herbicide applications to place before crops emerge. Proper application helps provide a good competition-free environment for crops to begin their development.

Pre-Emergence Herbicide Applications

Pre-emergence herbicide applications will be taking place before crops emerge. Proper application helps provide a good competition-free environment for crops to begin their development.

Utility adjuvants are added to pesticide tank mixes to improve spray mix characteristics such as spreading, penetration, droplet size, volatility and drift reduction.

When to Use Utility Adjuvants

Utility adjuvants are added to pesticide tank mixes to improve spray mix characteristics such as spreading, penetration, droplet size, volatility, and drift reduction.

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