Quinclorac Crabgrass Killer: Post-Emergent Spot Treatment Guide

The Mechanism: Why Quinclorac is the Post-Emergent Standard

Quinclorac is a synthetic auxin herbicide (HRAC Group 4) that mimics the plant hormone indole-3-acetic acid (IAA). When absorbed by the foliage and roots of susceptible weeds like smooth and large crabgrass, it triggers uncontrolled, disorganized cell division. This results in severe epinasty (twisting and curling of stems), chlorosis (yellowing), and eventual necrosis. Unlike contact herbicides that only burn the leaves, quinclorac is systemic, translocating through the plant's phloem and xylem to destroy the root system.

While pre-emergent herbicides like prodiamine remain the first line of defense, NC State Extension notes that post-emergent control is necessary when pre-emergent barriers fail or when crabgrass emerges from deep soil cracks. Quinclorac stands alone as the most effective post-emergent option for mature crabgrass in cool-season lawns and Bermudagrass.

Selecting Your Quinclorac Crabgrass Killer (Products & Costs)

Not all quinclorac formulations are identical. The concentration and added solvents dictate the price and efficacy. As of 2026, here are the primary professional-grade options available to homeowners:

• Drive XLR8 (BASF): The industry gold standard. Contains 1.5 lbs of quinclorac per gallon. The XLR8 formulation includes built-in solvents that improve leaf penetration. Expect to pay $55 to $68 for a 16 oz bottle.
• QuinKill Max (PBI Gordon): A direct generic competitor with the same 1.5 lbs/gal concentration. Usually priced slightly lower, around $45 to $55 for 16 oz.
• Fertilome Weed-Out with Crabgrass Control: A consumer-grade, ready-to-spray or diluted version. While cheaper upfront ($25-$35), the lower concentration and lack of professional surfactant packages make it less reliable for mature, multi-tiller crabgrass.

The Surfactant Requirement: Don't Skip the MSO

Quinclorac has a waxy cuticle penetration barrier. Applying it without a surfactant will result in a 40% to 60% reduction in efficacy. You must use a Methylated Seed Oil (MSO), not a standard Non-Ionic Surfactant (NIS). MSO modifies the surface tension of the spray droplet and actively dissolves the epicuticular wax on the crabgrass leaf, driving the active ingredient into the tissue. Mix MSO at a 0.5% v/v rate (approximately 1.3 fluid ounces per gallon of water).

Step-by-Step Spot Treatment Protocol

The most common mistake homeowners make with spot treatments is diluting the herbicide dose. Spot treatment requires the exact same rate per 1,000 square feet as a broadcast application; you are simply delivering that dose in a smaller volume of water directly to the weed patch.

1. Prepare the Turf: Do not mow for 2 days prior to application. Crabgrass needs maximum leaf surface area to absorb the systemic herbicide.
2. Mix the Solution: Fill your pump sprayer halfway with water. Add the quinclorac, agitate, then add the MSO surfactant. Fill the rest of the tank and agitate again.
3. Apply at the Right Time: Spray in the early morning or late evening when temperatures are between 65°F and 85°F. Ensure no rain is forecast for at least 6 hours.
4. Spray Technique: Use a flat-fan nozzle held 12 to 18 inches above the turf. Walk at a steady pace, ensuring the crabgrass is thoroughly wet but not to the point of runoff (dripping).
5. Post-Application Wait: Do not mow for 2 to 3 days after spraying to allow maximum translocation to the roots.

Turfgrass Safety Matrix: Who Can Use Quinclorac?

Quinclorac is highly selective, but it will severely damage or kill certain warm-season grasses. Always verify your turf type before mixing a tank. According to UMass Extension, misapplication on sensitive grasses causes severe stunting and chlorosis that can last for months.

Troubleshooting: Why Your Spot Treatment Failed

If your crabgrass is still thriving two weeks after application, one of the following failure modes is likely responsible:

• Targeting 3-to-4 Tiller Crabgrass with a Single Pass: Quinclorac struggles to kill large, multi-tiller crabgrass in one application. The label explicitly requires a second application 14 to 21 days after the first for mature weeds. If you only sprayed once, the initial shock killed the primary tillers, but secondary tillers recovered.
• Applying in High Heat (>85°F): When temperatures exceed 85°F, crabgrass closes its stomata to conserve water, halting herbicide uptake. Furthermore, spraying auxin herbicides in high heat drastically increases the risk of phytotoxicity (chemical burn) to your desirable turf.
• Using the Wrong Surfactant: If you used a basic dish soap or a standard Non-Ionic Surfactant (NIS) instead of an MSO, the herbicide likely sat on the waxy leaf surface and evaporated before penetrating the cuticle.
• Mowing Too Soon: Mowing 12 hours after application physically removes the treated leaf tissue before the systemic active ingredient has time to translocate down to the crown and roots.

"When spot-treating late-season crabgrass in August, the plant is already shifting its energy toward seed production rather than vegetative growth. Translocation slows down. For late-summer applications, ensure you are using the maximum 0.73 fl oz rate per 1,000 sq ft and be prepared for a slower visual kill—it may take 21 days to see complete necrosis compared to 10 days in early June."

Managing the Aftermath and Preventing Return

Once the crabgrass turns brown and brittle, rake out the dead debris to expose the bare soil beneath. Crabgrass is an opportunistic pioneer species; leaving a bare patch in your lawn simply invites the next wave of weed seeds to germinate. Immediately following the removal of the dead weed mat, overseed the spot with a turf-type tall fescue or Kentucky bluegrass blend matching your existing lawn. Keep the new seed moist and apply a starter fertilizer to ensure the desirable grass outcompetes any remaining crabgrass seeds in the soil seed bank.