Climate Change & Weed Management: Forages

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 Forage

Photosynthetic pathwayCommon name
(Scientific name)
CO2TemperatureDroughtReference Number
C3​Common ragweed
(Ambriosia artemisiifolia)
+ (S+R) | – (R)ND​1498
C3​Rescuegrass
(Bromus cartharticus)
=ND​ND​17
C3​Common lambsquarters
(Chenopodium album)
ND​21018
C3​Canada thistle
(Cirsium arvense)
ND​ND​24519
C3​Quackgrass
(Elymus repens)
ND​ND​245
C4​Yellow nutsedge
(Cyperus esculentus)
=ND​ND​7

Other Herbicides Efficacy in Forage

Herbicide 
(Trade name) 
Commodity
Herbicide group numberPhotosynthetic pathwayCommon name 
(Scientific name)
CO2TemperatureReference number
2-4, D4C3Wild buckwheat 
(Polygonum convolvulus)
+ND16
Atrazine 
(Aatrex®)
5C3Velvetleaf 
(Abutilon theophrasti)
ND+4
Common ragweed 
(Ambriosia artemisiifolia)
ND+4
Barley 
(Hordeum vulgare)
ND+16
Bromoxyynil 
(Maestro®)
6C4Kochia 
(Kochia scoparia)
=ND16
Dicamba 
(Clarity®)
4C4Kochia 
(Kochia scoparia)
ND4
Imazethapyr 
(Pursuit®)
2C3Chickweed 
(Stellaria media)
=ND16
Metolachlor 
(Dual Magnum®)
15C4Smooth pigweed 
(Amaranthus hybridus)
ND+11
Paraquat 
(Gramoxone®)
22C3Horseweed 
(Conyza canadensis)
ND14
C4Common waterhemp 
(Amaranthus tuburculatus)
ND15
Large crabgrass 
(Digitaria sanguinalis)
ND15
Sethoxydim 
(Poast®)
1C3Wild oat 
(Avena fatua)
=ND16

Management Recommendations

     Herbicide efficacy is expected to change under future climate conditions. In New York we are likely to see changes in herbicide efficacy as carbon dioxide (CO₂) and temperature levels increase, causing irregular precipitation patterns and making weed management even more difficult. In our search of scientific literature for research on herbicide efficacy under climate change conditions, a total of twenty-four experiment-based papers and two review-based papers reported on herbicide efficacy in forage cropping systems. Nine of these papers reported on glyphosate studies.  Four additional papers reported on six other chemistries: 2,4-D, sethoxydim (Poast®), bromoxynil (Maestro®), atrazine (Aatrex®), dicamba (Clarity®), and paraquat (Gramoxone®). These papers evaluate 45 weed species, of which only 47% (20 species) are currently in New York. Here we focus on these specific herbicide chemistries and these 20 species to provide relevant management recommendations for New York farmers. 

Other Climate Factors

  • Drought 
    • One review paper looked at sethoxydim (Poast®) and its effectiveness to control goosegrass (Eleucine indica, C4), which showed reduced efficacy. 
  • Airborne dust 
    • One experiment-based paper studied glyphosate and paraquat (Gramoxone®), both of which had reduced efficacy when controlling wild mustard (Sinapis arvensis, C3). 
  • UV-B Radiation 
    • Another experiment-based paper studied velvetleaf (Abutilon theophrasti, C3) and redroot amaranth (Amaranthus retroflexus, C4) when applying paraquat (Poast®), which resulted in a decrease in efficacy. 
  • Interacting Factors 
    • In addition to single climate factors, one experiment-based paper looked at the interaction of elevated CO₂ and higher temperatures and their combined effect on two species present in New York. Downy brome (Bromus tectorum) and prickly lettuce (Lactuca serriola) experienced no changes in glyphosate efficacy. One paper (reference 1) studied different doses of imazethapyr being applied to susceptible and resistant biotypes of barnyardgrass (Echinochloa crus-galli). Susceptible biotypes both maintained and showed an increase efficacy, these differences are based on different weed populations. Resistant biotypes for the weed populations both experience a decrease in efficacy.  

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 forage 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