Weed killers, also known as herbicides, are chemical substances designed to control or eliminate unwanted vegetation, offering a way to maintain landscapes and garden areas. Proper application is necessary to ensure the product works as intended, maximizing its effectiveness against target plants. Following correct procedures helps minimize unintended damage to desirable plants and reduces environmental exposure. Using these products requires a measured approach for successful weed management and safety.
Selecting the Correct Product
The first step in effective weed control involves selecting the right product for the specific problem. Herbicides are classified as either selective or non-selective. Selective herbicides target specific plant types, such as killing broadleaf weeds like dandelions while leaving grass unharmed, making them suitable for lawns. Non-selective herbicides are toxic to nearly all plants they contact and are used where total vegetation control is desired, such as on driveways or patios.
A critical distinction is between pre-emergent and post-emergent herbicides, referring to the timing of application relative to the weed’s life cycle. Pre-emergent herbicides are applied to the soil before weed seeds germinate, creating a chemical barrier that stops growth. This type prevents annual weeds like crabgrass from establishing themselves. Post-emergent products are applied directly to weeds that are already actively growing above the soil surface.
Herbicides also come in different formulations, primarily liquids and granules. Liquid formulations, which can be ready-to-use or concentrated, allow for more precise spot-treatment and better coverage on weed foliage. Granular products are generally easier to apply over large areas using a broadcast spreader and are frequently combined with fertilizer, known as “weed and feed” products. Granules typically require moisture from dew or watering to release the active ingredient into the soil.
Essential Preparation Steps
Before application begins, thoroughly read the product label, as it contains specific instructions for mixing, application rates, and safety precautions. Application equipment must be prepared, involving cleaning residue from previous products or calibrating a granular spreader to the correct setting. Proper calibration ensures the herbicide is not under-applied, which reduces efficacy, or over-applied, which can damage desirable plants.
Personal protective equipment (PPE) is necessary when handling herbicides, especially concentrates. This includes wearing chemical-resistant gloves, safety glasses, and long-sleeved shirts and pants to minimize skin contact. If using a liquid concentrate, accurate mixing is required, involving measuring a precise volume of product into water to achieve the correct concentration. Improper dilution can lead to poor results or phytotoxicity (chemical damage to plants).
Application Techniques and Timing
Achieving even coverage is important for efficacy and preventing streaks of dead or untouched weeds. When applying liquid sprays, use a consistent, sweeping motion to lightly coat the weed foliage without causing the solution to drip or run off. Be mindful of wind, as spray droplets can easily drift onto non-target plants, causing unintended damage. Avoid application when wind speeds are above 10 to 15 miles per hour. Liquid formulations are best suited for spot treatments, allowing for targeted application.
For granular applications, use a calibrated spreader, walking at a steady pace to ensure uniform distribution across the area. Overlapping slightly with each pass helps prevent untreated strips, but excessive overlap can lead to too high a concentration. Granular products often need to be watered into the soil immediately after application, or applied when the foliage is wet with dew, to activate the herbicide.
Timing the application to environmental conditions and the plant’s growth phase significantly impacts results. Post-emergent herbicides are most effective during the weed’s active growth phase, typically when temperatures are between 65°F and 85°F. High temperatures (above 85°F) can cause weeds to slow their metabolism, reducing chemical uptake and increasing the risk of the product volatilizing into a harmful vapor.
Rainfall is another consideration. For post-emergent contact killers, a rain-free period is needed after application to allow the product to be absorbed before being washed away. This required time, known as the rainfast period, varies by product. Conversely, many pre-emergent and granular products rely on being watered in, either by irrigation or light rain, to move the active ingredient into the soil to form the protective barrier.
Post-Application Care and Safety
Immediately after application, all equipment must be cleaned to prevent corrosion and cross-contamination. Spray tanks and nozzles should be thoroughly rinsed with water. The rinse water must be disposed of properly according to label instructions, often by spraying it over a previously treated area. Any remaining concentrated product should be stored in its original container with the label intact, kept in a cool, dry, and locked location away from children and pets.
A necessary safety measure is observing the re-entry interval (REI), the time people and pets must stay off the treated area. For most residential liquid applications, keep pets and children off the lawn until the spray has completely dried, which can take a few hours to a full day depending on humidity and temperature. Some labels specify a longer interval, and following this instruction prevents accidental exposure. Empty product containers should be disposed of according to local waste regulations, often by rinsing them and placing them in the trash or recycling if permitted.