Mesotrione is a selective systemic herbicide used in turf and lawn management to control unwanted plant growth without harming desirable turfgrass species. It is absorbed by target plants through their leaves, shoots, and roots, providing both preventative and curative control against a broad range of weedy grasses and broadleaf plants. This analysis details the specific weeds Mesotrione targets and outlines the proper timing and strategy for its effective application.
The Mechanism of Action
Mesotrione functions by inhibiting the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD). This enzyme is crucial in the biochemical pathway that produces plastoquinones and tocopherols. Plastoquinones are necessary for creating carotenoids, which are pigments that protect a plant’s chlorophyll from excessive light energy.
When Mesotrione blocks carotenoid production, the plant can no longer protect its chlorophyll, leading to rapid degradation upon exposure to sunlight. The visible result is that treated weeds turn white or bleached, starting at the growing points. This whitening effect precedes the ultimate death of the susceptible plant.
Mesotrione is selective because desirable turfgrasses, such as Kentucky Bluegrass and Perennial Ryegrass, rapidly detoxify the compound. These tolerant grasses quickly break down the Mesotrione molecule into harmless byproducts. This rapid metabolism prevents the chemical from accumulating to toxic levels, ensuring the turf remains green while susceptible weeds die.
Specific Weeds Controlled
Mesotrione provides control over more than 40 different broadleaf and grassy weeds in turf and ornamental settings. The herbicide is particularly successful against annual species.
Grassy Weeds
Mesotrione is valuable for controlling annual grassy weeds, especially in newly seeded areas where other herbicides would prevent turfgrass germination. It provides excellent pre- and post-emergent control of crabgrass (large and smooth). The herbicide is also highly effective against other troublesome grass species, including:
- Barnyardgrass
- Foxtail
- Goosegrass
The active ingredient can also suppress perennial grasses difficult to manage with conventional treatments, such as creeping bentgrass and nimblewill. Furthermore, Mesotrione provides reliable control over yellow nutsedge, a sedge species often mistaken for a grass.
Broadleaf Weeds
The herbicide offers strong control over numerous common broadleaf weeds. It is effective in managing various types of clover (white and large), though established perennial clover may require a follow-up application. Highly susceptible targets often problematic during cooler seasons include:
- Common chickweed
- Henbit
- Mouseear chickweed
Mesotrione also works well on pervasive perennial broadleaf weeds like dandelions and buckhorn plantain. Established, mature perennial weeds may require a second application two to three weeks after the initial treatment for complete elimination. The product is also labeled for control of ground ivy (creeping Charlie) and oxalis.
Application Timing and Strategy
The efficacy of Mesotrione depends on applying it at the correct stage of weed development and turf establishment. The product is unique because it can be used for both pre-emergent and post-emergent control.
For pre-emergent control, the herbicide is applied to the soil surface to prevent susceptible weed seeds from sprouting. This timing is beneficial when establishing new cool-season turfgrass because Mesotrione does not inhibit the germination of desirable grasses like Kentucky Bluegrass or Tall Fescue. The application must be watered in lightly to activate the chemical barrier, providing residual protection for three to four weeks.
For post-emergent control, the application targets visible, actively growing weeds, absorbing the chemical through the foliage. To ensure maximum absorption, a non-ionic surfactant (NIS) must be included in the spray mixture. The surfactant helps the solution adhere to the leaves, increasing the herbicide’s translocation throughout the plant.
After a post-emergent application, avoid watering the treated area for at least 24 hours to allow sufficient absorption. Always wear appropriate personal protective equipment when mixing and applying the concentrated product. Spot treatments typically require accurate mixing ratios to treat localized weed infestations effectively.