Dicamba is a selective herbicide in the chlorophenoxy family of chemicals. It comes in several salt formulations and an acid formulation. These forms of dicamba have different properties in the environment. Products with dicamba frequently contain other herbicides as well.
Dicamba is an herbicide, which can be used pre and post-emergent. It is known for its power against perennial broadleaf and 2,4-D herbicide-resistant weeds. Dicamba is also knows as 3,6-dichloro-methoxybenzoic acid, as this is its chemical name. This substance is commonly used on nonagricultural crops, such as lawns, but people also use it for ornamental plantings, public and rail-roads rights-of-way and on uncultivated, open areas. To be more specific, it is used on broadleaf, brush, vines and woody plants. It can be applied to the leaves or to the soil.
Dicamba controls annual and perennial broadleaf weeds in grain crops and grasslands, and it is used to control brush and bracken in pastures. It will kill broadleaf weeds before and after they sprout. Legumes will be killed by Dicamba (3, 5). Combined with a phenoxyalkanoic acid or another herbicide, Dicamba be used in pastures, range land, and non-crop areas (fence-rows, roadways and wastage) to control weeds.
Dicamba is a selective, acid herbicide, it is a member of the benzoic family of chemicals. This substance is not that effective on all weeds. Most people use Dicamba as a sole active ingredient or with multiple other active ingredients in producing finished herbicides.
Dicamba is often combined with other herbicides such as 2,4-D or glyphosate, complicating the prediction of its persistence. Other factors affecting degradation are salts, surfactants and chemicals such as ethylene glycol, often grouped under the rubric of inert ingredients, that break down differently — or not at all.
Products containing dicamba may be liquids, dusts or granules. Products may be concentrated or ready-to-use. Currently, dicamba can be found in over 1100 products that are sold in the United States. It is used in agriculture, residential areas, and other sites.
Always follow label instructions and take steps to avoid exposure. If any exposures occur, be sure to follow the First Aid instructions on the product label carefully.
Physical properties
In its purest stage, Dicamba is odorless, white, solid, crystalline. Its technical acid is a pale buff crystalline solid. Its technical material is a stable one, which is resistant to hydrolysis and oxidation under normal conditions.
Under normal temperatures and pressures, Dicamba is stable, but it can be a fire hazard if it is exposed to heat or flame. In the presence of strong oxidizers, Dicamba poses a fire and explosion hazard.
When Dicamba decomposes, thermally, it releases toxic and corrosive fumes of chlorides and toxic oxides or carbon.
Dicamba is volatile and it presents a drift hazard.
How does Dicamba act?
Dicamba uses the natural plant auxins against them, as it similar to the 2,4-D herbicide. These hormones help to control plant growth. When plants are treated with dicamba, they grow in abnormal and uncontrollable ways, and often, the plants die. Dicamba is used on many broadleaf weeds and woody plants. This creates multiple blockages in the plant’s vascular system, reducing the movements of glucose and nutrients, eventually strangling the plant. This is why when the weed grows, it dies. Dicamba will leave the plant with an uncontrolled cell division and growth and with damaged cell membranes.
Dicamba percolates down into the soil and is degraded by microbes and water to form salts, chlorides, acids — and carbon dioxide. Half of the substance degrades within 30 to 60 days, depending on the amount of herbicide used, the moisture in the soil and microbial action present. This halfway point is known as its half-life. The next half-life of 30 to 60 days sees degradation of 25 percent of the compound and so on, reducing by half — and so on and so on for 180 days to a year until only 1.5 percent remains. Ultraviolet light hastens the process, but, short of a laboratory pass-through, the herbicide must get into the open — in a stream or river — to encounter UV light.
Dicamba is water soluble and highly mobile in soils, leading to its movement into water tables and bodies of water. Although water hastens the half-life of Dicamba, it does not degrade the chemical — it just facilitates its percolation through soil into the water table — or into the storm sewer. It retards nitrogen-fixing bacteria and certain algae, but encourages certain fungal growth. Once the compound is in the open, it is mildly toxic to birds, fish and honey bees.
Dicamba does not bind to soil particles and is highly soluble in water. It is therefore highly mobile in the soil and may contaminate groundwater. Its leaching potential increases with precipitation and the volume applied.
Possible side effects
Pure dicamba is low in toxicity if breathed. If inhaled, people may experience dizziness, and irritation of the nose, resulting in coughing. If you get pure dicamba on your skin, it is low in toxicity, however skin irritation may develop. If you get dicamba in your eyes, it is moderately toxic. If dicamba is swallowed, people have reported symptoms such as vomiting, loss of appetite and muscle spasms. If a large amount is swallowed, diarrhea and abdominal pain have been reported. In humans, dicamba is not absorbed through the skin very well. If swallowed, dicamba is taken in quickly. Following dicamba’s uptake, the chemical is rapidly eliminated in the urine, mostly unchanged. In some individuals, dicamba is a skin sensitizer and it may cause skin burns.
Pets may be exposed to dicamba if they come into contact with plants that have been treated with dicamba, either by eating the plants or walking through an area where dicamba was applied. Signs that a dog or a cat may have been exposed to dicamba include shortness of breath, muscle spasms and the animal may produce a lot of saliva. Birds may also be exposed to dicamba by eating dicamba granules and signs include wing drop, a loss of controlled movements, and weakness. Dicamba is not likely to harm fish because of its low toxicity. Among several studies in fish exposed to dicamba, results showed that dicamba was relatively non-toxic to fish.
All Dicamba containing products must bear the “Warning” sign.