A lawn fungicide is a chemical or biological agent applied to turfgrass to control fungal diseases like dollar spot, brown patch, or rust. These products function by either preventing infection or stopping the growth of an existing fungus. Proper application is paramount for effectiveness, ensuring the treatment reaches the target area at the correct concentration. Following label instructions precisely minimizes environmental impact and protects the health of the applicator and those using the lawn. This guide details the necessary steps for preparing the turf, applying the product, and ensuring post-treatment safety.
Preparing the Lawn and Selecting the Fungicide
Effective treatment begins with selecting the appropriate product based on the identified disease and its stage of development. Fungicides are broadly classified into two categories: contact and systemic. Contact fungicides remain on the surface of the grass blades, forming a protective barrier that prevents new fungal spores from penetrating the plant tissue.
These surface-level treatments often interfere with the fungus through multiple biochemical pathways, resulting in a lower risk of resistance development. Because they only protect the tissue they cover, contact fungicides must be applied preventatively and usually require more frequent reapplication.
Systemic fungicides, by contrast, are absorbed into the grass plant and move throughout its vascular system. This allows them to offer both protective and curative action, treating infections that have already entered the plant tissue. Systemic products are longer lasting, often remaining effective for several weeks, and they can protect new grass growth that emerges after the application.
Mowing the turf 24 hours before treatment is advisable, as this exposes the grass crown and ensures the fungicide contacts the target surface. This also prevents the fungicide from being immediately removed by mowing after it has been applied.
Checking the weather forecast is important, as rain or high winds can wash away or cause drift, rendering the application ineffective. Review the product label to determine if the lawn should be dry or if light pre-watering is necessary to enhance absorption. Gathering personal protective equipment (PPE), such as chemical-resistant gloves, eye protection, and a mask or respirator, is mandatory before handling any product.
Step-by-Step Application Methods
Calibration is the most important step, ensuring the precise amount of active ingredient is delivered to the target area. This prevents under-dosing or chemical burn from over-application. For liquid applications, calibration involves determining the output volume of the sprayer over a measured area while walking at a consistent pace.
An applicator can mark a test area, such as 1,000 square feet, fill the sprayer with plain water, and time how long it takes to walk and uniformly cover the area. By collecting the output of the nozzle for that measured time, the applicator determines their unique application rate, such as gallons per 1,000 square feet. Once the rate is established, the required amount of concentrated product is mixed with the determined volume of water.
When mixing liquid concentrates, it is recommended to fill the tank halfway with water first, then add the measured chemical, and finally top off the tank with the remaining water while agitating the mixture. When applying the mixed liquid, maintaining a steady, even walking speed is necessary to ensure uniform coverage across the entire turf surface. The sprayer nozzle should be held at a consistent height above the grass to create a uniform spray pattern. To avoid missed strips and achieve the best coverage, the technique involves slightly overlapping each pass.
For granular products, the application relies on selecting the correct setting on the spreader dial as specified on the product label. The dial setting controls the flow rate of the granules, which is necessary for delivering the correct amount of active ingredient per area. Both rotary (broadcast) and drop spreaders require the applicator to walk in straight lines at a consistent pace to maintain an even distribution.
Many professionals recommend applying the total amount of product in two passes, using half the recommended rate each time. For example, the first pass can be made horizontally across the lawn, and the second pass made vertically. This cross-hatch pattern reduces the risk of streaking or uneven treatment by ensuring coverage. Achieving a uniform application across the entire treated area is the foundation of effective fungicide treatment.
Post-Treatment Care and Re-Entry Safety
Post-treatment care must immediately follow the instructions on the product label, particularly regarding watering. Systemic fungicides often require watering shortly after application to move the active ingredient from the leaf surface into the soil and root zone where it can be absorbed. This “watering in” is usually done within 24 hours, but the specific timing and volume are product-dependent.
Conversely, contact fungicides must remain on the surface of the grass blades to form a protective barrier. Therefore, if a contact product was used, watering must be avoided for a specified period to prevent the fungicide from being washed off the leaf tissue. In both cases, consulting the label is the only way to determine the correct post-application watering schedule.
The Re-Entry Interval (REI) is a regulated safety requirement dictating the minimum time that must pass before people or pets can safely enter the treated area. For many turf fungicides, the REI is stated as “until the spray has dried,” which is common for water-based applications. However, depending on the chemical’s toxicity, the label may specify a fixed time, such as four, twelve, or twenty-four hours.
It is essential to strictly observe the longest specified interval if multiple products were mixed and applied. After the waiting period, the final step involves cleaning and storing the equipment and any remaining product. Application equipment should be thoroughly rinsed to prevent chemical residue from degrading the components. Unused fungicide or empty containers must be stored or disposed of according to local regulations and the product label directions.
Fungicide application is rarely a one-time treatment, and the disease life cycle often requires follow-up applications. To maintain long-term effectiveness and prevent the fungus from developing resistance, it is advisable to alternate between products with different modes of action for subsequent treatments. Consistent monitoring of the lawn and proper cultural practices, such as correct watering and mowing, remain the best defense against recurring fungal issues.