Pale, off-color patches in an otherwise uniform green lawn are a common source of frustration for homeowners. This “white grass” phenomenon is a general term describing invasive grasses or weeds whose color contrasts sharply with the desired turf. These disruptive patches are typically caused by species that grow faster, have a lighter hue, or go dormant at a different time than the surrounding lawn. Successfully removing these unwanted grasses requires a precise, multi-step approach that begins with accurate identification.
Identifying the Specific Invasive Grasses
Before selecting a control method, it is crucial to determine the exact species causing the discoloration, as removal strategies differ significantly. Two likely culprits in North American lawns are the annual Japanese Stiltgrass (Microstegium vimineum) and the perennial Nimblewill (Muhlenbergia schreberi). Japanese Stiltgrass is a summer annual with a pale, blue-green color and a distinctive silver or white mid-rib stripe down the center of its short, lance-shaped leaves. This invasive species thrives in shady, moist areas but can tolerate full sun, spreading aggressively by setting copious amounts of seed in late summer.
Nimblewill, a warm-season perennial grass, forms dense, fuzzy, grayish-green patches that stand out against cool-season turf during the hot summer months. Nimblewill spreads through weak, wiry stolons (above-ground runners) which root at the nodes to form new plants, making it difficult to pull completely. It is distinguishable by its fine texture and preference for moist, shady environments, though it can persist in sunny spots. If the pale color is uniform across the entire lawn, the issue may instead be a temporary nutrient deficiency, such as a lack of nitrogen or sulfur, causing general chlorosis (pale-green color).
Non-Chemical Removal Techniques
For small, isolated patches, mechanical removal is a viable first step for homeowners avoiding synthetic chemicals. Japanese Stiltgrass is an annual with a shallow, fibrous root system, making it easy to pull by hand, especially when the soil is moist. The most effective time to hand-pull or mow Stiltgrass is in late summer, ideally between late August and early September, just before the plant sets seed. Mowing or trimming at this time prevents the plant from dispersing seeds, which can remain viable in the soil for up to five years.
Nimblewill, being a perennial with spreading stolons, is less suited to simple hand-pulling, as root fragments allow the plant to regenerate. For this weed, a more aggressive approach is necessary, such as digging out the entire patch, including the roots and surrounding soil. For larger, heavily infested areas where the turf is compromised, soil solarization is a non-chemical option. This process involves covering the moistened area with clear plastic sheeting for four to six weeks during summer, using solar energy to heat the soil to temperatures lethal to the weeds and their seeds.
Cultural practices like promoting a dense, healthy lawn naturally suppress weed growth. Maintaining turf at the highest recommended mowing height encourages deep root growth and shades the soil, inhibiting the germination of light-dependent weed seeds. Regular aeration ensures the soil is not compacted, allowing for better nutrient uptake, which helps the desired grass outcompete invasive species.
Targeted Herbicide Application
When mechanical methods are impractical for large infestations, a targeted herbicide application offers the most efficient control, though correct product and timing are essential. The highly selective herbicide Mesotrione (often sold as Tenacity) is the industry standard for Nimblewill control in cool-season lawns. Mesotrione is a systemic bleaching herbicide; it interferes with the plant’s ability to photosynthesize, causing the Nimblewill patches to turn white as they die over two to three weeks.
Since Nimblewill is a perennial grass that spreads via stolons, a single application is rarely sufficient for complete elimination. Effective control requires two to three applications of Mesotrione, spaced two to three weeks apart, applied when the weed is actively growing in late spring or early summer. While Quinclorac is effective against other annual grasses like crabgrass, it provides poor control of both Japanese Stiltgrass and Nimblewill. For Japanese Stiltgrass, the most effective selective post-emergent herbicide is Fenoxaprop-p-ethyl, found in products like Acclaim Extra.
Herbicide application must be done before Stiltgrass sets seed in late summer to break the cycle of re-infestation. Always combine selective post-emergent herbicides with a non-ionic surfactant. This improves the herbicide’s uptake by penetrating the plant’s waxy leaf surface, significantly boosting efficacy. Regardless of the product chosen, always adhere strictly to the label instructions concerning application rates, temperature restrictions (generally below 85°F), and safety precautions.
Long-Term Prevention Strategies
The final step in eliminating white grass is preventing its return by building a strong, dense turf canopy. For Japanese Stiltgrass, which germinates earlier than common weeds like crabgrass, pre-emergent herbicides are a foundational preventative measure. Active ingredients like Prodiamine or Pendimethalin must be applied two to three weeks earlier than the crabgrass window (late winter or very early spring) to form a chemical barrier before Stiltgrass seeds sprout.
Following the removal of the invasive grass, overseeding is necessary to fill bare spots and deny new weeds the opportunity to establish. The ideal time for overseeding with cool-season grasses is early autumn, when cooler air temperatures and warm soil promote rapid germination and establishment. Preparing the area by lightly raking the soil surface improves seed-to-soil contact, and maintaining a consistently moist seedbed is necessary until the seedlings are established.
A comprehensive soil test, conducted every one to two years, is important for maintaining turf health. This test provides a detailed analysis of the soil’s nutrient profile and pH level, which influences nutrient availability to the grass roots. Most turf varieties thrive in a slightly acidic to neutral pH range of 6.0 to 7.0. Correcting imbalances with applications of lime (to raise pH) or sulfur (to lower pH) creates an environment that favors desired turf over opportunistic weeds.