Diuron is a herbicide designed to manage unwanted plant growth. It belongs to the urea class of herbicides and is a white, crystalline solid in its pure form. As a systemic herbicide, it is absorbed by plants and transported throughout their system. Diuron controls both annual and perennial broadleaf weeds and grasses, making it a versatile tool for vegetation management.
Diuron’s Mechanism of Action
Diuron works by interfering with a biological process in plants: photosynthesis. It acts as a Photosystem II (PSII) inhibitor. This herbicide binds to a site on the D1 protein within the Photosystem II complex, located in the thylakoid membranes of plant chloroplasts. This binding disrupts the electron transport chain, which converts light energy into chemical energy for plant growth.
By blocking electron flow, diuron prevents the plant from producing adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH). Without these, the plant cannot fix carbon dioxide or produce necessary nutrients for survival. This disruption also forms reactive oxygen species, causing oxidative damage to leaf tissues, including cell membrane peroxidation. This damage results in visible symptoms like chlorosis (yellowing) and necrosis (tissue death), ultimately leading to the plant’s demise. Maximal inhibition of photosynthesis often occurs within minutes at higher concentrations.
Where Diuron is Used
Diuron is used to control a broad spectrum of weeds. In agriculture, it serves as both a pre-emergent and post-emergent herbicide, meaning it can be applied before weeds germinate or after they have emerged. Common crops include cotton, sugarcane, potatoes, citrus, and alfalfa. In cotton, it is frequently used for “layby” weed control and as an active ingredient in defoliants, aiding harvest preparation.
Beyond agriculture, diuron is used for total vegetation control in non-crop areas. These applications include industrial sites, railway lines, roadsides, and rights-of-way, where complete elimination of plant growth is desired. It is also found in forestry applications and for managing aquatic weeds, such as filamentous algae and certain submerged plants like bladderwort and naias. The herbicide targets annual grasses like crabgrass, barnyardgrass, and foxtail, as well as broadleaf weeds such as pigweed, lambsquarters, and purslane.
Environmental and Health Safety
Diuron’s properties raise environmental and health considerations due to its persistence and mobility. It is persistent in soil, water, and groundwater, with an average field dissipation half-life around 90 days. Its low tendency to bind to soil particles, especially in low organic matter or coarse soils, increases its potential for leaching into groundwater and runoff into surface waters. Diuron has been detected in surface water at concentrations ranging from 2.7 to 2849 parts per billion (ppb) and in groundwater from 0.34 to 5.37 ppb.
Diuron in aquatic environments poses risks to non-target organisms, especially aquatic life. It is moderately toxic to fish (48-hour LC50 values: 4.3-42 mg/L) and moderately to highly toxic to aquatic invertebrates (LC50 values: 1-2.5 mg/L). Even at low concentrations (0.1 ppb), diuron can reduce photosynthesis in aquatic plants. Concerns also exist about its impact on beneficial soil microbes if nitrogen turnover or carbon mineralization are affected by more than 25%.
Regarding human health, exposure to diuron can occur through dermal contact, inhalation, or ingestion. Acute exposure may cause irritation to the skin, eyes, nose, and throat. Chronic exposure can lead to damage to the developing fetus and effects on liver function. The U.S. Environmental Protection Agency (EPA) has classified diuron as a “known/likely” human carcinogen, based on studies showing increased incidences of bladder, kidney, and breast cancers in laboratory animals. It has also been shown to cause genetic damage in developing embryos and bone marrow cells in mice, and reduce birth weights in laboratory animals exposed during pregnancy.
To mitigate these risks, strict safety precautions are advised during handling and application. Workers should wear personal protective equipment (PPE), including gloves, eye protection, and protective clothing, to minimize skin and eye contact. Proper application methods, such as using low spray pressure, are crucial to reduce spray drift, especially near sensitive crops or water bodies. Safe storage practices are also important, ensuring the product is kept away from food, drink, and animal feed. Responsible disposal of the herbicide and its containers is necessary to prevent environmental contamination, and regulatory agencies establish restrictions on application rates and locations to manage potential risks.