The fall of 2018 brought many challenges to the region, making it difficult for fall anhydrous applications or a fall burndown. The February issue of CropTalk had the first part of this series. We hope to give you insight on options for spring management if you did not finish your traditional fall fieldwork. The first article, available on the Beck's website, focused on considerations for applying spring anhydrous. This article will focus on how to maximize the efficacy of a spring burndown.

Managing Marestail in the Spring

Marestail has an extended germination period, meaning it can germinate in the fall or spring. Marestail that germinates in the fall overwinters as a rosette and bolts in the spring. Germination in the spring can happen very early, just as soil temperatures start to rise. Whether the plant germinates in the fall or spring, controlling marestail when it is small is the key. Rosettes are much easier to control compared to plants that have bolted.

This means an EARLY burndown is key. How early? Applications should be made as air temperatures start to rise and the plants are actively growing for the herbicide to be effective. A spring burndown not only controls marestail, but also allows you the opportunity to control early emerging summer annuals like giant ragweed.

What Are My Control Options in the Spring?

In the spring, there are very effective options when it comes to marestail control. Products such as Sharpen® result in very effective control of marestail and giant ragweed, though most populations are resistant to glyphosate. Tank-mixing Roundup PowerMAX® with Sharpen can help control winter annuals that are susceptible to glyphosate, such as shepherd’s-purse, henbit, purple deadnettle, penny cress, etc. Reducing vegetation can also help eliminate areas for cutworm moths to lay their eggs in early spring.

A burndown offers the opportunity to use other herbicide modes of action (MOAs) and sites of action (SOAs) that cannot be used in-season. Gramoxone® tank mixed with metribuzin can be very effective on smaller marestail plants. This also allows the opportunity to use a group 22 + 5 herbicide, which cannot be used in-season.

What about Growth Regulators?

Growth regulators are very effective on marestail, even after the plant has bolted. Products such as 2,4-D, tank mixed with glyphosate, are very effective on marestail, and giant ragweed. However, as Enlist E3™ soybeans become available, we need to start looking at other burndown options such as Sharpen, Gramoxone and metribuzin to avoid over-reliance on 2,4-D. Dicamba is also very effective on marestail and giant ragweed. However, another MOA should be used to avoid over-reliance on dicamba if Xtendimax® is applied in-season to Roundup Ready 2 Xtend® soybeans.

Does This Change My Pre-emergence Application?

Products like Gramoxone will not have any residual value, while products such as Sharpen and metribuzin can have residual activity depending on the rate. The burndown application needs to be applied early enough to control the marestail while it’s small. However, this leaves more time in between the burndown and pre-emergence application.

This may allow new flushes of weeds, reducing the efficacy of the pre-emergence application. Pre-emergence herbicides need to reach the soil surface to be effective. If planting is delayed, select burndown products that have residual value such as Sharpen and metribuzin. For the pre-emergence application, select products that have residual and post-emergence activity or, add a product with post-emergence activity. Remember, this is only intended to clean up a few escapes. If there is heavy weed pressure, a second burndown application is needed to ensure the preemergence herbicide reaches the soil.

Individual results may vary. Always read and follow label directions.