Early Spring Soybean Weed Control: Managing Giant Ragweed and Kochia

Kochia and giant ragweed are formidable broadleaf soybean weeds that share many similarities, enabling you to scout for and manage them in tandem.

Here’s how chemical and cultural practices can help mitigate the risks of these weeds in soybean.

Kochia and giant ragweed: two early-season soybean weeds

(BASF + Matt Lavin)

Because they are similar, kochia and giant ragweed are often susceptible to the same chemical and cultural control methods. Here’s a breakdown of their shared traits to help you simplify your control protocol:

1. Early and long emergence timeframe

Both giant ragweed and kochia can germinate early, with most emergence coming in the first two to three weeks of the season, though additional emergence can occur almost all season long.

Kochia can germinate as early as January and continue to emerge into July. Giant ragweed seedlings first emerge in March and can continue into early August.

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2. Short seed life and fast germination

Both giant ragweed and kochia have a short seed life and fast germination, meaning early control of these soybean weeds is key to greatly reducing or eliminating them. More than

95% of kochia seeds die after two years.¹ Similarly, less than 1% of giant ragweed are viable by the end of the same period.²

By providing complete control and allowing no seed production in the first two years following a year with weed escapes, you can effectively rid the field of these weeds. If possible, delay tillage before planting in problem fields to control the large first flush of these weeds that germinate early in the season.

High potential for yield reduction

Giant ragweed grows quickly and can reach heights of up to 17'. Just one giant ragweed plant per 110 sq. ft. can reduce yields by up to 50%.³

Kochia’s erect plants feature stems between 1' and 4' high and can quickly overtake soybeans. Early-emerging kochia can reduce soybean yields by 70% or more.⁴

Herbicide timing for soybean weed control

Effective control of kochia and giant ragweed is achievable with a one-two punch of pre-emergence and post-emergence herbicides. Always read and follow the product label and instructions before application.

Pre-plant and burndown herbicides for soybeans

Tillage or burndown herbicides can help you control emerged weed populations before planting. Sharpen® is among the most effective burndown herbicides and works best when applied before planting. It also offers residual weed control. 2,4-D is often used as a burndown tank-mixed with Sharpen.

Your pre-emergence herbicide list for soybeans

Consult your pre-emergence herbicide list and apply soybean pre-emergence herbicide when soil temperatures are warm enough for weed germination and before weed emergence to reduce germination and target seedlings. Verdict® herbicide is a strong option for giant ragweed control.

Post-emergence herbicide for soybeans

Foliar application of a post-emergence herbicide for weeds in soybean should be made when kochia plants or giant ragweed are between 3" and 4", or as directed by the label. Liberty® ULTRA herbicide and 2,4-D are good post-emergence control options for giant ragweed in emerged soybeans. Both can be applied in a tank mix with glyphosate.

Time your herbicide application carefully. For example, herbicide applications to kochia are ineffective when applied during the early button stage, when dense leaf hairs can hinder foliar absorption.⁵

Non-chemical soybean weed control

Rotate your soybeans with crops that work well with delayed seeding and pre-seeding tillage to keep weed populations more manageable. Clean equipment thoroughly to avoid transferring weed seeds between fields.

Fall-sown cover crops can also limit weed pressure. For example, triticale has been found to reduce kochia densities up to 94%.⁶

Cereal rye works well to suppress giant ragweed. Research indicates that at least 3,500 pounds of dry cereal rye biomass per acre could effectively reduce giant ragweed density by up to 50%.⁷

Reach out to your nearby extension office agent or a company professional like your regional BASF representative with questions about control of soybean weeds.

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Endnotes

1. Patterson, Eric. Kochia scoparia: Basic Research in Biology and Ecology. Colorado State University Weed Science, Dec. 2019,https://agsci.colostate.edu/weedscience/wp-content/uploads/sites/84/2019/12/Patterson_KochiaBiologyEcology_BasicResearch.pdf. Accessed 26 Jan. 2026.
2. “Giant Ragweed (Ambrosia trifida L.).” Weeds Extension, Department of Plant, Soil and Microbial Sciences, Michigan State University,https://www.canr.msu.edu/weeds/extension/giant-ragweed. Accessed 26 Jan. 2026.
3. Johnson, Bill, et al. “Biology and Management of Giant Ragweed.” University of Delaware, www.udel.edu/content/dam/udelImages/canr/pdfs/extension/weed-science/GWC12_GtRagweed.pdf. Accessed 26 Jan. 2026.
4. “Kochia Management in Soybeans.” MU Extension, 2018, extension.missouri.edu/media/wysiwyg/Extensiondata/Pub/pdf/miscpubs/mx1135.pdf. Accessed 26 Jan. 2026.
5. Westra, Eric P. “Kochia.” Getting Rid Of Weeds, Grow - Integrated Weed Management, 25 June 2024, growiwm.org/weeds/kochia/. Accessed 26 Jan. 2026.
6. “Kochia.” Agricultural Biology, Colorado State University, 28 Dec. 2023, agsci.colostate.edu/agbio/imp-pests/kochia/. Accessed 26 Jan. 2026.
7. Wele, Rodrigo. “Cereal Rye Cover Crop Vs. Giant Ragweed.” Cover Crop Strategies, 2 Jan. 2024, www.covercropstrategies.com/articles/3029-cereal-rye-cover-crop-vs-giant-raweed. Accessed 26 Jan. 2026.