The World of Auxin Herbicides
By Judd Fitzgerald
Judd is a product manager for Helena Chemical Company for the western United States in the turf, ornamental, pest control and vegetation management markets. He has over 18 years of industry experience. Judd lives in Denver, CO.
We are living in a constantly evolving world of herbicide technology, and thankfully, Helena Chemical Company is well-positioned to help guide you through it. What I’m referring to is the introduction of “auxin-ready” row crops. To the non-row crop industry, this may not seem like a significant advancement in weed management, but it is. It is a reflection of the incredible tool many of us already trust for effective weed control – auxin herbicides.
Auxin herbicides are a huge family of herbicides that began with 2,4-D in the 1940’s. Over the next 70 years, auxin herbicides expanded to include the sub-families of phenoxy, benzoic acid and pyridines. While each sub-family has a different mode of action, they are all growth regulators. They regulate cell division and elongation, and they can impact plant processes such as vascular tissue, meristem differentiation and leaf initiation.
The marvel of this chemistry is they are selective. Going back 70 years to post World War II, there were no herbicides that could be used selectively to control broadleaves. The auxin family of herbicides would change the world.
How do phenoxys work? (2,4-D, MCPP, MCPA) – Circa 1945
- Phenoxy herbicides mimic a naturally occurring plant chemical called indole acetic acid (IAA).
- They cause unregulated IAA production in the plant, which leads to uncontrolled growth, twisting, thickening, elongation and eventually death as the weed literally grows itself to death.
How does benzoic acid work? (dicamba) – Circa 1965
- Dicamba works by stimulating abnormal cell growth in meristematic cells.
- This results in the blockage of phloem vascular tissue.
- Extensive destruction of cambia and phloem cells near the meristems occurs.
- The plant is killed by starvation resulting from an inability to translocate needed energy in the phloem.
How do pyridines work? (triclopyr, fluroxypyr, picloram, aminopyralid, clopyralid, aminocyclopyrachlor) – Circa 1970 to today
- Pyridines affect proteins in the plasma membrane, interfere with RNA production and change the properties and integrity of the plasma membrane.
- They affect protein synthesis and increase RNA concentration. Auxin-like molecules prevent normal and necessary fluctuation in auxin levels required for proper plant growth.
- Cell proliferation increases, and the plant's vascular system becomes blocked because of excessive cell division. The resulting growth crushes the vascular transport system.
These 3 different sub-families are commonly blended in 2-way and 3-way products. Alone, they can control roughly 80 different weeds, but combined, they can control upwards of 200 different weeds. Residual control can occur with the combination of both the benzoic acid and pyridine classes, which allows for a broader control spectrum.
What is so fascinating about this family of herbicides is both the EPA and FDA has allowed the use of specific actives in the group on certain crops that have been genetically modified to resist their activity. This alone signals the safety of the chemistry on food crops. This also shows the confidence in the herbicide family to be limited in plant resistance development.
What does this mean to those of us controlling weeds but not growing food? Take solace in your use of 2,4-D, dicamba, triclopyr, fluroxypyr and aminopyralid. These are proven tools we have used for years, and because they do an incredible job controlling weeds, the commercial agriculture market is signaling they will be around for a very long time.
Although auxin herbicides are fantastic weed control tools, Helena recognized 20 years ago an opportunity to further improve the formulation systems delivering these highly useful actives. Targeting inherent issues with commercial formulations at that time, Helena developed a very unique, patented formulation platform known as Soluble Acid Herbicides. This formulation system improves overall weed control performance and tank mix compatibility while reducing volatility and characteristic auxin odors.
Today, Helena has experienced over 15 years of commercial success selling a number of herbicides based on this novel technology. Below are a few examples of how the Soluble Acid Herbicides are optimized to bring our customers greater weed control efficiency:
- Makes the spray solution act more like an oil.
- A plant leaf surface is lipophilic (oil loving). Applications are typically made with water-based spray applications that are lipophobic (oil hating). See the problem? Water-based sprays are repelled by plant surfaces. Helena’s Soluble Acid Herbicides are formulated with ingredients to make the water solution act more like an oil solution. This allows a greater rate and degree of leaf adhesion and absorption resulting in enhanced weed control. It also typically allows for the use of less active ingredient to attain the same results.
- Keeps the herbicide wetter longer on the plant.
- Herbicide gets into the plant by a process of diffusion (movement of higher concentration to lower concentration). This process occurs as long as the herbicide is in liquid form. Once the liquid dries, it crystalizes on the leaf surface and no longer diffuses into the plant. Because our acid herbicides are more oil-like, they have the ability to stay wetter longer and are less likely to evaporate.
- Makes the herbicide solution acidic.
- Most plant surfaces are anionic (negatively charged). Most tap water used to make spray solutions tends to be alkaline. Acidic solutions are usually positively charged and alkaline solutions are usually negatively charged. See the problem? Without augmenting our spray water to make it acidic, the leaf surface is less prone to receive the alkaline solution. All of the Soluble Acid Herbicides Helena produces have a buffered acidity. We do this to combat the alkaline water almost all of us encounter in spray solutions.
Soluble Acid Herbicide formulations provide the following product advantages:
- Adjuvant Inclusive
- Ability to Use Less Active Ingredient
- Reduced Odor
- Reduced Volatility
- Enhanced Deposition
- Enhanced Rainfastness
- Enhanced Absorption
- Fast Activity
- Greater Efficacy
Helena’s single acid technology products:
Helena’s commercial pre-mix acid products:
- Brush Rhap® – 2,4-D acid, Dicamba acid - (IVM)
- On Deck® – 2,4-D acid, Dicamba acid - (T&O)
- Trump Card®– 2,4-D acid, Fluroxypyr – (IVM)
Helena’s co-formulated herbicide products (do not contain acid technology):
- Battleship® III– Fluroxypyr, Triclopyr, MCPA (“In-Can” Adjuvant System) – (T&O)
- EndRun® – 2,4-D, Dicamba, MCPA (“In-Can” Adjuvant System) – (T&O)
Your Helena sales representative is well versed in these technologies and how they can be used to gain better weed control, reduce active ingredient load in the environment and potentially save you money. Helena is committed to leading the industry with new herbicide formulations and is dedicated to being your source for experience and quality products. Visit www.helenaprofessional.com now for more information on our acid technology herbicides.