The Foxtails: A Comprehensive Field Guy for Knowing & Controlling Your Weeds

Three familiar weeds in corn and soybeans are the foxtails: giant, green, and yellow. Most fields have a mix of these foxtail species, with giant being the most common, but green is more prevalent in the northern states. 

All are summer annual grasses that were introduced from China in the early 1900s. The foxtails are in the Poaceae family and are of the genus Setaria. The word setaria comes from the Latin term seta, which means bristle or hair. Their seed heads do resemble the tail of a fox, thus the “foxtails.”

Keys to Identify the foxtail species:  

Seed head comparison:

Although it is quite easy to distinguish between the foxtails late in the season with their different seed heads, this would be too late to use in a herbicide selection decision. 

📸: BASF Contributing Writer/Featuring a close up shot of giant, green and yellow Foxtail seed heads.

Ligule comparison:

One key to identifying the foxtails early is to examine the collar region and look at the ligule. Yellow foxtail has very long (up to 1/2 inch) and sparse ligule hairs, while giant and green have short ligule hairs.

Leaf Blade Hair Comparison:

A second identifier early in the season is looking for hair on the leaf blade. The most distinguishable is giant foxtail, which has short hairs on the upper side of the leaf blade resembling a crew cut and is visible when you hold it to the light. Yellow foxtail has very long and sparse hairs on the upper side of the leaf blade, while green foxtail has no hairs on the leaf blade. We were taught to remember some of this with the saying "green is clean."

📸: BASF Contributing Writer/Featuring closeup shots of distinguishing characteristics in Giant Foxtail (Setaria faberi - Left), Green Foxtail (Setaria viridis - Middle), and Yellow Foxtail (Setaria pumila - Right).

Giant Foxtail: Setaria faberi 

As its name implies, giant foxtail is the largest of the three weedy foxtail species and can grow as tall as two to four feet. The seed head is large and can be up to 8 inches long, so much so that it bends over from its’ weight and has a characteristic droop. Rolling the stem between your fingers, you can determine it has a round stem.

Green Foxtail: Setaria viridis 

This plant can have a lot of variability but is usually shorter than the other foxtails. Some green foxtail biotypes, including robust purple foxtail, robust white foxtail, and giant green foxtail, can reach 3 to 4 feet in height. The seedhead bends a little, but not as much as giant foxtail. It also has a mostly round stem.

Yellow Foxtail: Setaria pumila

Also known as pigeon grass in the northern plains, it has a flat stem that is noticeable when rolling it between your fingers. This foxtail tillers early and can withstand mowing, so it is more common on lawns and roadsides than the other foxtails. It flowers later in the summer, and its' erect seed head can sometimes make a glistening yellow border along roadsides. 

Foxtail Management with Herbicides:

In general, the foxtails are not highly competitive and can be managed effectively with a good crop stand and the use of herbicides. Comparing the three species, yellow foxtail can be harder to control with many postemergence herbicides than the other foxtails.

Effective Weed Management for Corn

In corn, the use of group 15 soil-applied herbicides such as Outlook^® Herbicide or Zidua^® Herbicide offers good control. Post-applications of group 27 herbicides such as Armezon^® Pro Herbicide, group 9 glyphosate, or group 10 Liberty® Herbicides are also effective.

Effective Weed Management for Soybeans

In soybeans, group 15 soil-applied herbicides such as Outlook^® Herbicide, Verdict^® Herbicide or Zidua^® Herbicide offer good control. Post-applied group 10 Liberty^® Herbicide, group 9 glyphosate, and group 1 Poast^® Herbicides are also effective.

Herbicide resistance of the foxtails has been documented for group 5 atrazine, group 1 acetyl CoA carboxylase post-grass herbicides, group 2 ALS, and group 3 DNA herbicides in the US.

📸: @zhikun sun via Canva/Featuring a close up shot of a common weed known as green foxtail (Setarria viridis).

Foxtail Weed Look-a-Likes

Fall panicum can be confused for green foxtail as it also has a hairy ligule and no hairs on leaf blade, but you will not find hairs on the fall panicum’s leaf sheath, whereas green foxtail’s leaf sheaf margin does have hairs. As Fall panicum gets larger, it has a light-colored mid-vein on the leaves, and its nodes on stems are somewhat swollen. 

Foxtail barley has a seed head that looks more like a broom than a foxtail and is a native perennial grass found in pastures and marginal areas.

This content is being brought to you in partnership with Grow Smart^® Live and contributing guest authors. BASF provides the information in this article as a service to its customers; however, the views expressed by guest writers are their own and do not necessarily reflect the views of BASF.

Always read and follow label directions. Grow Smart, Outlook, Zidua, Armezon, Liberty, Verdict and Poast are registered trademarks of BASF. All other trademarks are the property of their respective owners and use of any such trademark does not imply any affiliation with or endorsement by its owner. © 2024 BASF Corporation. All rights reserved.