Wild violets (Viola spp.) are perennial broadleaf plants that are a tenacious and frustrating weed in manicured turfgrass. These plants, with their distinct heart-shaped leaves and springtime purple, blue, or white flowers, spread aggressively to form dense patches that compete directly with lawn grasses. The challenge in controlling them lies in finding a treatment that can eliminate this persistent broadleaf invader while leaving the surrounding narrow-leaf turfgrass completely unharmed. The key to successful removal is understanding the plant’s biology and applying specialized selective chemistry at the optimal time of year.
Why Wild Violets Are Difficult to Control
Wild violets are difficult to control because their physical characteristics provide strong natural defenses against typical weed control methods. The plant’s leaves are covered in a thick, glossy, waxy cuticle, a layer that functions to repel water and, consequently, liquid herbicides. This protective barrier prevents many common contact weed killers from penetrating the leaf surface and being absorbed into the plant’s system.
Beneath the soil, the plant possesses an extensive root system with fleshy, horizontal underground stems known as rhizomes. These creeping rhizomes allow the violet to spread rapidly and regenerate quickly, even if the above-ground foliage is completely destroyed. Simply pulling the visible plant or spraying with a general herbicide that only kills the top growth is often ineffective, as the plant can rapidly sprout new shoots from the undamaged underground network.
Selective Active Ingredients That Spare Grass
The solution to selective control lies in a group of systemic compounds known as synthetic auxins, which mimic a plant growth hormone. These herbicides, which include 2,4-D, Dicamba, and MCPP, are often formulated together into what are commonly called “three-way” broadleaf weed killers. A more effective compound for wild violets, however, is Triclopyr, a synthetic auxin that is particularly potent against woody and tough perennial broadleaf weeds.
These selective herbicides function by exploiting a fundamental biological difference between broadleaf plants (dicots) and grasses (monocots). When a susceptible broadleaf plant absorbs the synthetic auxin, the chemical overwhelms the plant’s natural growth regulation system. This causes uncontrolled cell division and elongation, ultimately leading to distorted growth and stem twisting.
Turfgrass, which is a monocot, possesses a biological tolerance to these growth regulators. Grass plants restrict the translocation of the herbicide within their structure and possess metabolic pathways that can rapidly break down the chemical into an inactive form. Furthermore, grasses lack the vascular cambium, a layer of dividing cells present in dicots, which is a primary target of the synthetic auxins. This inherent difference allows the compounds to devastate the wild violet while leaving the lawn undamaged.
Optimal Timing and Application Techniques
Application timing is the most influential factor for successful control. The most effective period to apply a systemic herbicide is in the fall, typically from late September through November, when the plant is preparing for winter dormancy. During this time, the wild violet begins to move stored carbohydrates and nutrients from its leaves down to its root system and rhizomes for overwintering.
Applying the herbicide during this downward flow means the chemical is effectively pulled along with the nutrients, ensuring it reaches and kills the entire underground root and rhizome system. Treatments made in the spring or summer often only kill the visible leaves, allowing the underground rhizomes to survive and push up new growth later. For maximum absorption, the active ingredient must make contact with the difficult waxy leaf surface.
To overcome the violet’s water-repellent cuticle, a non-ionic surfactant, often called a spreader-sticker, should be mixed with the herbicide solution. This additive reduces the surface tension of the spray droplets, allowing the chemical to spread across the waxy leaf and penetrate the cuticle.
Due to the plant’s resilience, multiple applications are usually required, often two to three treatments spaced several weeks apart, to completely exhaust the regenerative capacity of the rhizomes. Applications should also be avoided when temperatures are too high or too low, with daytime temperatures generally above 55°F being ideal for active chemical uptake and translocation.