General Herbicide Efficacy Trends
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.
The lack of research on herbicides other than glyphosate limits information on effective substitutions in weather where glyphosate is less effective. Most research has also been conducted on a small group of studied weed species, so there are many common weeds with no available information on changing herbicide efficacy.
Elevated CO₂
- C3 weeds will grow larger more quickly
- C4 weeds maintain current growth rate
Elevated CO₂ and Higher Temperatures
- May limit plant growth (C3 and C4)
- Resilient C3 plants will outgrow treatment window more quickly, shortening management reaction time
Herbicide Resistance
- Susceptible and resistant biotypes will react very differently to herbicide applications under future climate change conditions
Herbicide Chemistries
- Individual chemistries important to consider when managing weeds
- Glyphosate (group 9) efficacy is expected to decrease
- Atrazine (group 5, e.g., Aatrex®) is expected to increase
- Halosulfuron (group 2, e.g., Sandea®) may maintain efficacy
Glyphosate Efficacy Changes in Corn and Soy
In our search of scientific literature for research on herbicide efficacy under climate change conditions, a total of twenty experiment-based papers were conducted in corn and soy cropping systems. Glyphosate was studied in nineteen of these papers, with only seven other chemistries addressed (glufosinate (Liberty®), 2,4-D, MCPA, halosulfuron (Sandea®) — used in corn only; bentazon (Basagran®), fomesafen (Reflex®) – used in soy only; and linuron (Lorox®) – used in both corn and soy). Thirty-seven weed species were evaluated in these papers, of which only fourteen are currently in New York. Here we focus on glyphosate and these fourteen species to provide relevant management recommendations for NY farmers.
Table 1. Changes in glyphosate efficacy on 14 weeds present in NY, including photosynthetic pathway (C3 or C4) and glyphosate efficacy change under three climate factors: elevated CO₂, higher temperatures, and drought conditions.
Interacting Climate Factors
In addition to single climate factors, four papers looked at the interaction of elevated CO₂ and higher temperatures and their combined effect on 7 species – 5 of which are in New York. Species with no glyphosate efficacy changes were downy brome (Bromus tectorum) and prickly lettuce (Lactuca serriola). Lambsquarters(Chenopodium album) showed a reduction in efficacy. A mixture of glyphosate and 2,4-D was applied to horseweed (Conyza canadensis) and common reed (Phragmites australis), which resulted in a decrease in efficacy.
Weed Management Recommendations
Adapting weed management strategies to account for these changes is imperative. It will become more important to know your weeds and target them with the most effective available chemistry for the weather conditions expected during the treatment window. For management recommendations on corn, please visit the CALS Field Crops Corn Weed Control page. For soy weed management, please visit the Soy Weed Control page. Growers can refer to the current Cornell Pest Management Guidelines or talk to an extension specialist for more information on best practices in weed management and herbicide rotation.
References
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