Tip •  2023-04-17

Five tips to make your post-emergence herbicide application a success

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sprayer in soybean field

1. Start with a two-pass weed control strategy

Starting with a two-pass weed control management strategy offers the greatest advantage over weeds, allowing a burndown or pre-emerge residual application to set a clean slate for controlling weeds. This solution also makes post-emergent weeds more manageable and provides more flexibility when it comes to the post-emergence pass.

2. Target weed size

The general rule of thumb is to tackle weeds as early as possible. An early post-emerge application will target weeds when they are smaller and easier to control, when crops are more tolerant in the growing early stages. Mike Cowborough, Field Crops Weed Management Specialist with the Ontario Ministry of Agriculture and Food reminds farmers that when annual weeds get beyond 10 cm tall, they are harder to manage and require higher rates of glyphosate in order to get acceptable control.

Check product labels for any specified weed growth and leaf stages to ensure you’re using the right product for the most effective control. The Corteva Agriscience™ Field Guide App is a great resource to help find weeds each product will control along with weed ID images to help you identify which weeds you have in your field.

3. Make the right mix

Always read the product label for recommended volume, spray droplet quality and any specific adjuvant requirements.

According to Tom Wolf of Sprayers 101, the decision on which application method is best for herbicides boils down to two main factors: (a) target type and (b) mode of action. He provides a handy chart to select the appropriate water volume and spray quality based on modes of action here.

Here are a few water volume reminders to keep in mind as you tank mix post-emergent applications:

  • Don’t skimp on water volume, opt for the mid to higher water volume recommendations on the product label.
  • A good rule of thumb is that 15 gallons/acre will work for most post-emergence herbicides and fungicides.
  • Increase water volumes to 20 gallons/acre if conditions are very dry, the crop canopy is very dense or the weeds are advanced, or if you’re spraying a contact only herbicide like Liberty® 200 SN.

4. Add the right surfactant

Product labels will detail the required surfactants. For many herbicides, including Corteva’s Classic™, Accent IS and other low use rate granules, surfactants are critical to ensure product spread on the leaf surface and penetrate through the weed’s waxy cuticle. If glyphosate is the tank-mix partner, you can often skip the surfactant. As always, read the label and if you have questions, contact your trusted agronomic advisor, retailer or local Corteva Agriscience™ Territory Manager.

5. Check weather conditions

Optimal conditions for most herbicide applications are when winds are between 3-16 km/hour. Always check weather conditions ahead of any application, taking note of the possibility of rain (to allow time for product uptake into target weeds) and temperature. Some products, like Liberty 200 SN work well in hot and sunny conditions, while others may not.

If possible, and under the right weather conditions, spray during daylight hours when herbicides perform better. As long as the wind conditions are right, a tank-mix like Enlist 1 and Liberty 200 SN will perform best when applied early afternoon under sunny conditions.

Be sure to check for temperature inversions before every application, especially at dawn or dusk. A temperature inversion (when a layer of warm air covers a layer of cooler air) can act like a lid and restrict air movement. Such an event can cause spray particles to become trapped in the warmer layer of air and stay suspended until wind movement increases, resulting in off-target movement. Never spray if you suspect a temperature inversion, because you risk damaging susceptible plants in nearby fields, lawns and gardens. For more information on weather and application timing, and tips on checking for temperature inversion, check out the Enlist Product Use Guide