Weed Control Considerations for Non-Glyphosate Tolerant Cotton
In 2023, Corteva’s US cottonseed brand, Phytogen, released a new GM cotton trait package, W3E1, targeting the southwest Cotton Belt region (Kansas, Oklahoma, Texas, and New Mexico). This trait package includes WideStike 3 for lepidopteran pest resistance as well as tolerance to Enlist One (2,4-D) and glufosinate. However, this trait package differs from the W3FE trait package Kansas cotton growers are used to in that it does not include tolerance to glyphosate. The varieties available since the 2025 growing season are PHY 136 and PHY 137. PHY 136 is an early- to mid-maturing variety, and PHY 137 is very early maturing.
Why consider non-glyphosate-tolerant cotton?
The primary motivation for producers to try these new varieties is reduced seed costs as the technology fee for glyphosate tolerance is omitted from the total seed cost. As seed cost is one of the greatest annual expenses in cotton production, this could be a significant cost-saving opportunity under the pressure of narrow profit margins. Additionally, non-glyphosate-tolerant cotton production systems open up the opportunity for using glyphosate in the off-season to control volunteer cotton in other phases of the crop rotation.
Grass and sedge control in non-glyphosate-tolerant cotton
Due to widespread glyphosate resistance in key weed species such as Palmer amaranth and kochia, the greatest weed control “loss” resulting from not spraying postemergence glyphosate will be grass control. The best options for postemergence grass control in non-glyphosate tolerant cotton are the Group 1 herbicides (Table 1). This includes herbicides like clethodim (Select, others) and quizalofop (Assure II, others). These products should be applied with COC or NIS for best activity. Glufosinate (Liberty, others) also has activity on grasses; however, it is less effective than glyphosate or a Group 1 product.
Glufosinate can also help manage nutsedge infestations. The ALS-inhibiting herbicides trifloxysulfuron (Envoke) and pyrithiobac can suppress yellow and purple nutsedge. In addition, S-metolachlor (Dual, others, and a component of Intermoc) can also suppress nutsedges.
Table 1. Grass and nutsedge response to selected cotton herbicides when applied according to label directions.
|
|
|
Annual grasses |
|||
|
Herbicide(s) |
Crop tolerance |
Barnyardgrass |
Crabgrass |
Fall panicum |
Foxtail |
|
Assure II |
E* |
E |
E |
E |
E |
|
Clethodim |
E |
G |
E |
E |
E |
|
Fusion |
E |
G |
E |
E |
E |
|
InterMoc (resistance cotton only) |
E |
G |
G |
G |
G |
|
Liberty and other glufosinate products (resistant cotton only) |
E |
G |
G |
G |
G |
|
Staple |
– |
– |
– |
– |
– |
|
Envoke |
|
|
|
|
|
|
|
|
Perennials |
|||
|
Herbicide(s) |
Crop tolerance |
Johnsongrass |
Yellow nutsedge |
- |
- |
|
Assure II |
E* |
G-E |
– |
- |
- |
|
Clethodim |
E |
G-E |
– |
- |
- |
|
Fusion |
E |
G-E |
– |
- |
- |
|
InterMoc (resistance cotton only) |
E |
F-G |
F |
- |
- |
|
Liberty and other glufosinate products (resistant cotton only) |
E |
F-G |
F |
- |
- |
|
Staple |
– |
– |
P-F |
- |
- |
|
Envoke |
|
|
P-F |
- |
- |
*E=Excellent, G=Good, F=Fair, P=Poor, and – weed not listed on the herbicide label.
Glyphosate injury to non-glyphosate-tolerant cotton
An added concern in non-glyphosate-tolerant cotton production systems is the potential for glyphosate injury from misapplication, tank contamination, or drift. When weed scientists in North Carolina sprayed 4-leaf cotton with drift rates of glyphosate, they reported a maximum of 13% yield loss following application of a 1/10 rate of glyphosate, with less than 1% yield loss caused by the 1/100 rate. However, at higher glyphosate rates (1/4 and 1/8), cotton lint yield was reduced, even though no visible injury was observed 7 weeks after application. Reductions were attributed to reduced boll set or delayed maturity. However, factors other than glyphosate rate can influence cotton yield loss caused by drift. Research conducted in Texas suggests that cotton yield loss is more likely when drift occurs during reproductive growth stages, and cotton yield loss was greater in high-yielding environments than in locations with drought stress in the North Carolina study.
For more detailed information, see the “2026 Chemical Weed Control for Field Crops, Pastures, and Noncropland” guide available online at https://www.bookstore.ksre.ksu.edu/pubs/CHEMWEEDGUIDE.pdf or check with your local K-State Research and Extension office for a paper copy.
The use of trade names is for clarity to readers and does not imply endorsement of a particular product, nor does exclusion imply non-approval. Always consult the herbicide label for the most current use requirements. Users should read and follow all label directions.
Sarah Ganske, Extension Weed Science Specialist
slancaster@ksu.edu
Logan Simon, Southwest Area Agronomist, Garden City
lsimon@ksu.edu
Patrick Geier, Weed Scientist - Southwest Research & Extension Center, Garden City
pgeier@ksu.edu