Herbicides are chemical agents used to control or eliminate unwanted vegetation, commonly referred to as weeds. The simple answer to whether these products kill grass is yes, they can, but the outcome depends entirely on the specific chemical formulation. The potential for a product to damage turfgrass is determined by a fundamental distinction: whether the herbicide is selective or non-selective. Understanding this classification is the first step toward effective lawn management.
Understanding Selective and Non-Selective Herbicides
Non-selective herbicides are designed to kill virtually every plant they contact, making no distinction between desirable turfgrass and weeds. Products containing the active ingredient glyphosate disrupt basic biological functions common to nearly all plant life, such as cell growth or protein synthesis. They are used for total vegetation control along fence lines, in sidewalk cracks, or when clearing an area for a new landscape project.
Selective herbicides are formulated to target specific types of plants while leaving others unharmed, making them ideal for lawn care. These chemicals exploit biological differences between plant groups to eliminate broadleaf weeds, such as dandelions or clover, without damaging turfgrass. Products containing active ingredients like 2,4-D, Dicamba, or MCPA are common examples of selective formulations.
How Herbicides Target Weeds Without Harming Grass
The mechanism allowing selective herbicides to spare grass involves differences in plant structure and metabolism between monocots and dicots. Turfgrasses are monocots, characterized by narrow, upright leaves, while most broadleaf weeds are dicots. This difference in leaf morphology means that spray droplets are less likely to be retained or absorbed efficiently by the smooth, vertical blades of grass.
Selective herbicides, such as synthetic auxins, interfere with specific metabolic processes unique to dicot plants. These chemicals mimic natural growth hormones, causing uncontrolled cell growth, tissue deformation, and eventual death in the broadleaf weed. Grasses possess a different metabolic pathway that allows them to quickly degrade the herbicide into a non-toxic form before it causes widespread damage.
Common Reasons Turfgrass Dies After Herbicide Application
Even when using a selective herbicide, turfgrass can still suffer significant injury, most often due to misapplication or environmental factors. Applying a product at a concentration higher than the rate recommended on the label can overwhelm the grass’s natural detoxification capability. This overdose prevents the grass from quickly metabolizing the chemical, leading to yellowing, dieback, and death.
Weather conditions during application are another frequent cause of damage, as turfgrass becomes more vulnerable when stressed. Applying herbicides when temperatures exceed 85°F can cause the grass to absorb the chemical more rapidly or increase the volatility of some formulations. This volatility allows the chemical vapor to move and injure surrounding plants, including the turf.
Choosing the wrong selective product for a specific grass type can also result in damage. Some turf varieties, such as Bentgrass, are highly sensitive to common selective herbicides like 2,4-D, even at labeled rates. Accidental exposure to non-selective chemicals is also a risk, often occurring through wind drift of spray particles onto the lawn from a nearby treated area.
Protecting Your Lawn During Herbicide Use
Protecting your lawn begins with strictly adhering to the product label, which specifies the correct application rate and the types of grass the product is safe for. It is important to calibrate spray equipment to ensure the correct volume of chemical is dispersed, avoiding the mistake of over-application.
Before applying any product, check the weather forecast and avoid spraying during windy conditions to prevent chemical drift onto non-target areas. Applying herbicides when the air temperature is cool, such as in the early morning or late afternoon, minimizes plant stress and reduces the risk of chemical volatilization. Keeping children and pets off treated areas until the spray has completely dried is a necessary safety precaution.