Climate Change & Weed Management: Soybeans

How to use the tables:

First, locate the right table for the herbicide you’re using

Glyphosate (also known as RoundUp®) has its own table, while all other herbicides are in a separate table

For the “Other Herbicides” table, identify the brand/chemical you use based on the name and the group number

Then, see if the table has data for a weed species you’re trying to manage (e.g. Lambsquarters)

You can then see how the performance of the herbicide against the weed will change under different climate conditions.

  • A red “-“ means the herbicide will be less effective as the climate factor increases
  • A green “+” means the herbicide will be more effective as the climate factor increases
  • A blue “=” means there will be no change in efficacy
  • A white “ND” means there was no research data for that interaction
  • S and R refer to susceptible or resistant biotypes (e.g. "-R" means efficacy is reduced against resistant biotypes)

Glyphosate Efficacy in Soy

Photosynthetic pathwayCommon name
(Scientific name)
CO2TemperatureDroughtReference Number
C3​Velvetleaf
(Abutilon theophrasti)
ND​ND​16
C3​Common ragweed
(Ambriosia artemisiifolia)
+ (S+R) | – (R)ND​1498
C3​Giant ragweed
(Ambriosia trifida)
ND​+ND​9
C3​Common lambsquarters
(Chenopodium album)
ND​21018
C3​Horseweed
(Conyza canadensis)
ND​10
C4​Smooth pigweed
(Amaranthus hybridus)
ND​+ND​12
C4​Redroot pigweed
(Amaranthus retroflexus)
=ND​ND​18
C4​Yellow nutsedge
(Cyperus esculentus)
=ND​ND​7

Other Herbicides Efficacy in Soy

Herbicide 
(Trade name)
Herbicide group numberPhotosynthetic pathwayCommon name 
(Scientific name)
CO2TemperatureReference number
2-4, D4C3Wild buckwheat 
(Polygonum convolvulus)
+ND16
Bentazon 
(Basasgran®)
6C4Smooth pigweed 
(Amaranthus hybridus)
 
ND+12
Glufosinate 
(Liberty®)
10C4Smooth pigweed 
(Amaranthus hybridus)
ND+12
Imazethapyr 
(Pursuit®)
2C3Chickweed 
(Stellaria media)
=ND16
Linuron 
(Lorox®)
5C3Wild buckwheat 
(Polygonum convolvulus)
ND4
5C4Smooth pigweed 
(Amaranthus hybridus)
ND+11
Metolachlor 
(Dual Magnum®)
15C4Smooth pigweed 
(Amaranthus hybridus)
ND+11
Metribuzin5C3Common lambsquarters 
(Chenopodium album)
=ND16
Paraquat 
(Gramoxone®)
22C3Horseweed 
(Conyza canadensis)
ND14
22C4Common waterhemp 
(Amaranthus tuburculatus)
ND15
Large crabgrass 
(Digitaria sanguinalis)
ND15
Sethoxydim 
(Poast®)
1C3Wild oat 
(Avena fatua)
=ND16

Management Recommendations

Credit to Vipan Kumar, Associate Professor at Cornell School of Integrative Plant Science Soil and Crop Sciences Section, and Bryan Brown, Senior Extension Associate at NYS Integrated Pest Management, for reviewing the following recommendations:

  • For alternative POST applications against many weeds, alternatives to Roundup® (Glyphosate, WSSA herbicide group 9) include Liberty® (Glufosinate, group 10), 2,4-D (group 4), and especially Clarity® (Dicamba, group 4). 
  • Diversifying your weed control options is beneficial to offset herbicide resistance and the potential of decreasing herbicide efficacy with climate change. Instituting cultural and/or mechanical practices, such as cover crops, competitive crop rotation, improve agronomic practices (seed spacing, timing, etc.) will help the crop out-compete the weed population. 
  • Other considerations include mechanical tools such as, strategic tillage, seed destructor technology, chaff lining, electric weeders, etc. Using precision, spot sprayers, or spray drones can reduce overall application amounts for more expensive alternatives to glyphosate. 
  • Applying preemergent herbicide in the spring or using a burn down application in fall can help if you have a large seedbank of horseweed. For PRE-herbicide applications consider Dual Magnum® (metalachlor, group 15), metribuzin (group 5), Valor®(flumioxazin, group 14), Classic® (chlorimuron, group 2), or the premix Panther PRO® (containing metribuzin, flumioxazin, and imazethapyr). 
  • Horseweed (Conyza canadensis) bolts more readily when exposed to higher temperatures in the early spring; timely management will be critical.

Other Climate Factors

Drought

  • Glyphosate (Roundup®, 9) was less effective when applied to velvetleaf (Abutilon theophrasti) under drought conditions (see reference 16). Two papers looked at annual sowthistle (Sonchus oleraceus). One of the papers found that efficacy decreased for a resistant biotype, (reference 13) while the other paper found no change in efficacy for resistant biotypes and an increase in efficacy for susceptible biotypes (reference 11).
  • Sethoxydim (Poast®, 1) was less effective when applied to goosegrass (Eleusine indica) under drought conditions (reference 15).

Decreasing Humidity 

  • Glufosinate (Liberty®, 10) was less effective against wild oat (Avena fatua), palmer amaranth (Amaranthus palmeri), redroot pigweed (Amaranthus retroflexus), common waterhemp (Amaranthus tuburculatus), and green foxtail (Setaria viridis) under low humidity (Reference 16).

Interacting factors

  • Four papers looked at the combined effect of elevated CO₂ and higher temperatures on seven species – five of which are in New York. Species with stable glyphosate efficacy were downy brome (Bromus tectorum) and prickly lettuce (Lactuca serriola) (reference 3). Lambsquarters (Chenopodium album) showed decreased efficacy (reference 10). A mixture of glyphosate and 2,4-D was applied to horseweed (Conyza canadensis) and common reed (Phragmites australis), which resulted in decreased efficacy (reference 9). One paper (reference 1) studied different doses of imazethapyr being applied to susceptible and resistant biotypes of barnyardgrass (Echinochloa crus-galli). Susceptible biotypes either maintained or showed increased efficacy, depending on source seed location. Resistant biotypes for the weed populations both experienced decreased efficacies. 

 

The efficacy of herbicides is expected to either decreaseincrease, or maintain effectiveness depending on the specific chemistryspecies, and climate factor(s) involved. This web page focuses on problematic weeds in soy cropping systems and provides data sourced from the current scientific literature to help build an understanding of how these future shifts might affect weed management. Please note that research to date has mostly focused on glyphosate, which limits information on effective substitutions in weather conditions where glyphosate is less effective. Additionally, only a small group of weed species have been studied, so there are many common weeds with no available information on changing herbicide efficacy. However, given the currently available literature, we conclude that photosynthetic pathway, herbicide resistance, and herbicide chemistries will have the most impact on efficacy and management.  

See our other web pages and fact sheets in this series for information on photosynthetic pathways, herbicide resistance effects, and climate change impacts for additional commodity areas. Growers should refer to the current Cornell Pest Management Guidelines for information on pesticides labeled for use in New York State. Contact an area extension specialist for current information on best practices in weed management and herbicide rotation.

 

Credits

This content was authored by Caroline Marschner, Sharon Bachman, Isabella Colucci, John Pirrung, Sophie Westbrook, and Toni DiTommaso. We would also like to express our gratitude again to Vipan Kumar and Bryan Brown for their invaluable support and expert input on this project and these fact sheets.

Disclaimers

Read the pesticide label prior to use. The label is the law.  The information contained on this page is not a substitute for a pesticide label. Trade names used herein are for convenience only; no endorsement of products is intended, nor is criticism of unnamed products implied.

This work was supported by a joint research and extension program funded by the Cornell University Agricultural Experiment Station (Hatch funds) and Cornell Cooperative Extension (Smith Lever funds) received from the National Institutes for Food and Agriculture (NIFA,) U.S. Department of Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

References