Pre-emergent herbicides are a common tool in lawn care, designed to stop weeds before they appear above the soil surface. These products offer a proactive approach to weed control, contrasting with treatments that target existing weeds. Because they are widely used in residential areas, a natural question arises regarding their safety for family members, including children and pets. This article explores the safety profile of these products and outlines the necessary steps for safe application.
Understanding Pre-Emergent Herbicides
A pre-emergent herbicide functions by creating a chemical barrier in the uppermost layer of the soil before weed seeds germinate. The active ingredients target the vulnerable process of cell division in the young root and shoot tissues of the sprouting seedling. This disruption prevents the seedling from developing a viable root system, effectively killing the plant before it breaks the soil surface. Pre-emergents must be watered into the soil to become active.
These products are typically sold in two main forms: granular and liquid concentrates. Granular formulations consist of the active ingredient coated onto small pellets and are applied using a spreader. Liquid concentrates are mixed with water and sprayed over the turf, offering faster activation and more uniform coverage. Both forms rely on moisture, either from irrigation or rainfall, to dissolve the chemical and establish the continuous barrier in the soil.
Human and Pet Exposure Risks
When used according to label instructions, most regulated pre-emergent herbicides have low toxicity to mammals. The primary health risk to humans stems from acute exposure during the mixing and application process. Direct contact with the concentrated product can cause mild irritation to the skin or eyes. Inhalation of fine dust or mist can also lead to temporary respiratory discomfort.
For pets, the risk is slightly higher due to their proximity to the ground and potential for accidental ingestion. Granular products pose a particular hazard if a pet ingests a significant quantity of the pellets before they are watered into the soil. While most active ingredients are classified as low-toxicity, ingestion can still lead to gastrointestinal upset, such as vomiting, diarrhea, or excessive drooling. The greatest risk occurs immediately following application and before the product has been fully absorbed into the soil.
Safe Application and Storage Guidelines
Minimizing exposure begins with utilizing appropriate Personal Protective Equipment (PPE) during application. This includes wearing chemical-resistant gloves, long pants, long-sleeved shirts, and closed-toe shoes to prevent dermal contact. When applying powdered or liquid formulations, using a mask or respirator and protective eyewear is advisable to limit inhalation and eye exposure.
Accurate application is a fundamental safety measure, requiring the spreader or sprayer to be calibrated to the rate specified on the product label. Over-application increases the chemical concentration, elevating potential risks to people and the environment. After application, the treated area must be watered in to move the herbicide into the soil profile and start the barrier formation. This step significantly reduces the risk of contact exposure.
Keep children and pets off the treated lawn until the product has been watered in and the area is completely dry. This waiting period, often 24 to 48 hours, allows the chemical to bind to the soil particles, making it less accessible for dermal contact or accidental ingestion. Proper storage is equally important, requiring the product to be kept in its original, sealed container in a locked area, out of the reach of children and pets.
Environmental Impact and Water Safety
Water Quality
Beyond direct contact risks, the use of pre-emergent herbicides carries broader environmental considerations, particularly concerning water quality. If applied incorrectly or before heavy rainfall, the product can be washed away in surface runoff. This movement can carry active ingredients into storm drains, contaminating nearby streams or other bodies of water. The presence of herbicides in waterways can be harmful to aquatic life, including fish and invertebrates.
Non-Target Organisms
Pre-emergents can also negatively affect non-target plants if misapplied. Overspray onto flower beds or near the root zones of desirable ornamental plants can inhibit their growth. Long-term or excessive use may affect beneficial soil organisms, such as microbes and earthworms. Following the label precisely, particularly regarding application rates and weather conditions, is the most effective way to prevent these ecological issues.