Broadleaf weeds are common invaders of turfgrass, distinguished from desirable grasses by their leaf structure. Unlike the parallel veins found in turf, broadleaf plants possess a network of netted veins and emerge from the seed with two initial leaves. The goal is to eradicate these unwanted plants without damaging the surrounding lawn. Various methods exist, ranging from manual removal to the precise application of chemical controls.
Mechanical and Organic Removal Methods
Manual removal is the most direct and chemical-free method for eliminating individual broadleaf weeds, especially those with taproots like dandelions. Using a hand tool, such as a specialized dandelion fork or weeding knife, allows for the extraction of the entire root structure. This process is easier and more effective when the soil is moist, as wet soil releases the taproot with less resistance and reduces the chance of root breakage.
For widespread or numerous weeds, non-chemical spot treatments offer an alternative. Horticultural vinegar, which contains a higher concentration of acetic acid, can effectively burn the foliage of small, young weeds upon contact. This method works by rapidly desiccating the plant tissue, but it often requires repeated application because the acid may not penetrate deeply enough to kill the root.
Boiling water poured directly onto the weed’s crown and leaves instantly destroys the plant’s cellular structure. Corn gluten meal functions as a natural pre-emergent, releasing peptides that inhibit the root growth of germinating seeds. This product must be applied before weed seeds sprout to be effective.
Using Selective Herbicides for Control
Chemical control offers an efficient method for managing large infestations of broadleaf weeds using selective herbicides. A selective herbicide targets the unique growth pathways of broadleaf plants while leaving turfgrass unharmed. This contrasts sharply with non-selective products, which kill nearly all vegetation they contact, including the lawn itself.
Most selective broadleaf weed killers contain a mixture of active ingredients designed to manage a wider spectrum of species. Common components include 2,4-D, Dicamba, and MCPP, which act as synthetic auxins, mimicking natural plant hormones. When absorbed, these chemicals cause uncontrolled, rapid cell growth in the broadleaf plant, leading to distorted stems and leaves, and ultimately, death.
Herbicides are categorized as either contact or systemic treatments. Contact herbicides destroy the plant tissue they touch and are best for small, annual weeds, but they may not kill the root of perennial weeds. Systemic herbicides are absorbed through the leaves and translocated throughout the plant, including down to the roots, providing more complete control over established perennial species.
Products are sold in various formats. Liquid concentrates or ready-to-spray formulas are effective for precise spot treatments or broadcast application. Granular products, often marketed as “weed-and-feed” fertilizers, combine the herbicide with nutrients. When selecting a product, confirm that the formulation is safe for the specific type of turfgrass present, as some ingredients can damage sensitive varieties like St. Augustine or Centipede grass.
Timing and Effective Application
The success of any broadleaf weed control method relies heavily on precise timing and application technique. Post-emergent herbicides, which target existing weeds, are most effective when the weeds are young and actively growing. This active growth phase typically occurs during the spring and early fall when temperatures are moderate, allowing the weeds to readily absorb and transport the chemical.
Apply herbicides when the air temperature is between 60 and 85 degrees Fahrenheit. Applying treatments above 90 degrees can increase the risk of damage to the turfgrass and cause the herbicide to volatilize, making it less effective. The application should also be made when no rain is expected for at least 24 hours to prevent the product from washing off the leaves before absorption.
To maximize absorption, withhold mowing for two days both before and after the application of a liquid post-emergent herbicide. Allowing the weeds to grow undisturbed ensures a larger leaf surface area is available to intercept the spray. The waiting period after application allows the systemic chemical sufficient time to translocate down to the root system.
For liquid sprays, ensure full and uniform coverage of the weed foliage without excessive runoff. Granular products require the foliage to be lightly damp, often achieved by applying in the early morning dew or shortly after a light watering, so the granules can stick to the leaves. Proper calibration of the spreader or sprayer is necessary to deliver the exact recommended rate, preventing both under-application and turf-damaging over-application.
Long-Term Weed Prevention
Shifting the focus to enhancing the health and density of the turf is the most sustainable approach to long-term broadleaf weed prevention. A healthy lawn forms a dense canopy that naturally crowds out and shades the soil, inhibiting the germination of weed seeds. Cultural practices that promote robust turf growth are the foundation of this preventative strategy.
The correct mowing height is a powerful tool in weed management, as taller grass blades create deeper root systems and cast more shade upon the soil. Mowing at the highest recommended height for the specific turfgrass variety, often between three and four inches, helps to keep the soil cooler and prevents sunlight from reaching dormant weed seeds. Removing no more than one-third of the grass blade length in a single mowing session avoids stressing the turf.
Proper watering practices are necessary to maintain a strong lawn capable of outcompeting weeds. Watering deeply and infrequently encourages the grass roots to grow deep into the soil, making the turf more resilient to drought and heat stress. Shallow, frequent watering keeps the upper soil layer constantly moist, which favors the germination of shallow-rooted weed seeds.
Following a fertilization schedule supplies the necessary nutrients to promote lateral growth and increase turf density. Providing the correct balance of nitrogen, phosphorus, and potassium at the proper times encourages the grass to spread and fill in any bare patches. A thick, well-fed lawn leaves little space or light for broadleaf weeds to establish themselves.