Species Overview

Scientific: Imperata cylindrica

Common: cogongrass, cogon grass, blady grass, Brazilian satintail, alang-alang, lalang, speargrass, sword grass

Family: Poaceae (grass family)

Introduction History: Introduced into the United States in the early 1900s as packing material and later intentionally for forage and soil stabilization. [7, 16, 18, 28, 29, 61, 66, 80]

Origin: Tropical and subtropical Asia [7, 57]

Species Characteristics

General Description: Perennial grass that forms dense, nearly monospecific stands. Leaves are upright, stiff, bright green to yellow-green, and characterized by an off-center white midrib and finely serrated margins. Silvery-white, plume-like seed heads are produced in spring and are conspicuous above surrounding vegetation. Spreads locally via sharp, white rhizomes that are belowground. Typically associated with disturbed habitats but can inhabit most soil, water, and light conditions found in Florida.

Detailed Description: Perennial, rhizomatous C₄ grass forming dense, monotypic stands. Produces extensive belowground rhizome networks that can comprise 36–80% of total plant biomass, supporting rapid vegetative spread and resprouting following disturbance [22, 36, 45, 66, 71, 83, 84]

Habitat: Occurs across a wide range of environmental conditions including dry uplands, pine flatwoods, and disturbed sites, but is most competitive in well-drained soils [40, 57]. Salt tolerant [11, 30, 42, 43, 86]

Invaded Range: Globally distributed across tropical and subtropical regions in agriculture, pasture, right-of-way, mines, and natural areas. In the United States, primarily concentrated in the southeastern Coastal Plain and present throughout most of Florida [7, 79, 87].

Leaves: Linear yellow-green blades with a distinct off-center midrib and finely serrate margins. [35, 36, 38, 60, 79, 80]

Flowers: Unbranched culm with silvery-white, compacted panicle. Flowering commonly occurs in spring or following disturbance [35, 39, 46, 67].

Rhizomes: Dense, scaly rhizomes typically located within15–40 cm (6—15.7 in) of the soil surface [13, 71, 80].

Impacts

Categorization/Regulation: FISC Category I; UF/IFAS Assessment: “Prohibited”; Federal Noxious Weed; Florida Noxious Weed

• Aggressive clonal expansion and rhizome dominance allow rapid spread [4, 26, 71].

• Forms dense monotypic stands reducing biodiversity [1, 5, 23, 25, 58, 80]

• Alters fire regimes by increasing fuel loads [33, 49, 53, 61, 75, 80]

• Broad abiotic tolerance contributes to invasion success of cogongrass [8, 9, 27, 40, 46, 52, 57, 61, 63, 68, 69]

• Anthropogenic dispersal is a major spread vector [9, 10, 55, 56, 65, 83, 84]

Prevent spread via equipment sanitation and limiting soil movement. Avoid disturbance in invaded sites. Maintain reporting systems to ensure active management efforts before populations are impactful.

Mow or prescribed burn prior to herbicide application to remove built-up thatch and promote active growth herbicide uptake. Do not mow when seed heads are present. Do not burn without a follow-up herbicide treatment.

Mechanical control through repetitive plowing or tilling is effective but only logistically feasible in agronomic settings or areas where non-target root damage is not a concern. Rarely suitable for natural areas due to costs, non-target root and seedbank damage and may increase spread through rhizome fragmentation [69, 83].

No approved biological control agents currently available [6, 64, 88, 89].

Foliar applications with glyphosate (2-5% v/v) and/or imazapyr (0.5-1% v/v) are most effective and should always include a compatible surfactant. Tank mixes of glyphosate + imazapyr provides greater and more persistent control [24, 62]. If using imazapyr, practitioners should use rates appropriate for the application site to avoid non-target damage. The label for the product provides specific instructions regarding non-target damage, maximum quantity per unit area, and replanting intervals.

Other ALS-inhibiting herbicides have demonstrated adequate control in combination treatments with imazapyr, though peer-reviewed validation remains limited [24, 57]. Glufosinate + imazapyr has been shown to be a potentially useful tank mix if glyphosate is not permitted [73]. Grass selective chemical applications with fluazifop-p-butyl have potential for use in restoration planning [44].

Treatment Timing:

Late-season applications improve herbicide translocation to rhizomes [2, 62, 85]. Peninsular populations which are not subject to freezing temperatures may remain green throughout the winter but experience drought-induced dormancy that may reduce the effectiveness of chemical treatment. Regardless of formulation applied, expect multi-year (2-3 years) follow-up monitoring and treatments [2, 57].