Diesel fuel will kill weeds, but this method is highly discouraged due to significant environmental and safety risks. Diesel fuel is a petroleum-based product composed of hydrocarbons that acts as a non-selective contact killer. While it destroys unwanted plant life on contact, using it as a herbicide introduces a hazardous chemical into the environment. The immediate effectiveness of diesel is outweighed by the long-term consequences to soil health and personal safety.
How Diesel Kills Plant Life
Diesel is not a targeted herbicide; instead, it causes rapid cellular destruction through physical and chemical means. When applied to the foliage and stem, the oil coats the surface. This coating dissolves the plant’s waxy cuticle layer, leading to rapid dehydration and tissue death.
The oily nature of the fuel prevents the exchange of gases, such as carbon dioxide and oxygen, suffocating the plant by blocking the stomata. The volatile organic compounds (VOCs) within the fuel are phytotoxic, directly poisoning the plant’s internal systems. If the fuel reaches the soil, the hydrocarbons chemically immobilize nitrogen, depriving the plant of this necessary nutrient.
Hazards of Using Fuel as a Herbicide
Applying diesel fuel to vegetation creates immediate physical hazards to property and human health. Diesel is flammable, and the vapors it releases can mix with air to become explosive, especially near dry plant material. This elevates the risk of fire, which can spread quickly through treated areas.
Direct contact with the fuel poses considerable health risks. Skin exposure can cause severe irritation, leading to dermatitis or eczema with repeated contact. Inhaling the fuel’s vapors can irritate the eyes and respiratory system, potentially causing central nervous system symptoms like dizziness and nausea.
The most severe hazard is chemical pneumonitis, a serious lung injury that can occur if aerosolized diesel droplets are inhaled or if the liquid is accidentally ingested and aspirated.
Long-Term Soil and Water Contamination
The long-term environmental damage caused by using diesel is extensive because the fuel is slow to degrade. Diesel is a mixture of total petroleum hydrocarbons (TPH), including polycyclic aromatic hydrocarbons (PAHs), which are persistent in the soil. These hydrocarbons are phytotoxic, meaning the soil becomes poisonous to new plant life, preventing the growth of desired plants for years.
The hydrophobic nature of the fuel causes it to coat soil particles, blocking microscopic pores. This reduces the soil’s air and water permeability and its water-holding capacity. Diesel contamination impacts the soil’s biological health by reducing the diversity and population of beneficial microorganisms and fungi.
This destruction of the soil food web, which includes earthworms, compromises the ecosystem’s ability to cycle nutrients and remain fertile.
Environmentally Sound Weed Control Methods
Safe and effective weed control involves using methods that do not rely on hazardous petroleum products. Physical removal methods, such as hand-pulling or hoeing, are effective because they remove the entire root system. Organic materials like cardboard or wood mulch can smother weeds by blocking sunlight, preventing germination and growth.
Heat is another non-chemical option, with boiling water poured directly onto the weeds to destroy the plant cells instantly. For spray application, horticultural vinegar, which contains a high concentration of acetic acid, dehydrates young or annual weeds on contact. For larger areas, approved commercial herbicides or specialized products like herbicidal soaps, which contain fatty acids, provide a more environmentally responsible solution.