Factors Limiting the Distribution of Cogongrass,Imperata cylindrica, and Torpedograss,Panicum repens

Abstract

Greenhouse, growth chamber, and laboratory studies were conducted to determine anatomical and morphological characteristics and cultural practices limiting the distribution of cogongrass, torpedograss, and johnsongrass in the United States. Cogongrass did not produce axillary buds along most of the rhizome nor regenerate when apical six-node-long rhizome segments were buried deeper than 8 cm. Both torpedograss and johnsongrass produced axillary buds along the entire lengths of their rhizomes. Torpedograss shoot emergence decreased at burial depths between 8 and 16 cm. Shoot emergence from johnsongrass rhizomes was not affected by burial as deep as 16 cm. Rhizomes of all three species were tolerant of desiccation. Cogongrass grew better in soil at pH 4.7 than in soil at pH 6.7, whereas torpedograss and johnsongrass grew equally well in either pH. It is postulated that cogongrass spread is limited by lack of axillary bud formation on most of the rhizome and the inability of rhizomes to send up new shoots if buried deeper than 8 cm. These factors could account for the intolerance of cogongrass to cultivation. Torpedograss appears to spread only vegetatively due to the lack of viable seed production.

Cogongrass (Imperata cylindrica) invasions in the US: Mechanisms, impacts, and threats to biodiversity

“…In experimental trials, cogongrass was shown to out-compete and displace bahiagrass (Paspalum notatum) seedlings, but was not able to colonize established bahiagrass stands . Additionally, it has been demonstrated that cogongrass inhibits bermudagrass (Cynodon dactylon) growth, but was less competitive than Johnsongrass (Sorghum halepense) (Wilcut et al, 1988). Competition studies utilized a combination of greenhouse, growth chamber, and natural areas settings (Table 1).…”

Imperata cylindrica, an alien invasive grass, maintains control over nitrogen availability in an establishing pine forest

“…It is a prolific seeder, producing as many as 3,000 seeds per plant (Holm et al 1977). Whether by seed or by rhizome, I. cylindrica can invade a variety of ecosystems from xeric uplands to shaded mesic sites (Jose et al 2002;Ramsey et al 2003) regardless of soil conditions, mostly favoring acidic soils (Wilcut et al 1988;Collins et al 2007). …”

Influence of Cultural Practices on Torpedograss Competition with Two Warm-Season Lawn Grasses

“…Although torpedograss is typically found in moist, sandy soils, it has been reported to grow on heavy upland soils (12,25,28). Environmental conditions such as acidic soils and occasional flooding do not appear to negatively affect torpedograss growth (28).…”

“…Poor torpedograss seed viability may indicate dissemination occurs primarily through vegetative propagation of rhizome‐contaminated soils (22,28). Torpedograss’ regenerates from rhizome fragments high in carbohydrate reserves (19,28). The rapid growth of torpedograss is capable of producing dense rhizome systems within a few months under favorable growing conditions (7).…”

“…Infrequent mowing and/or excessive mowing heights have been shown to increase weed competition for some weed populations in turfgrass systems (10). Unlike many weeds disseminated from seed that lack fully developed organs such as rhizomes for energy storage, torpedograss rhizomes have sufficient energy to support shoot re‐growth (28) above the interfering canopy. Torpedograss growth above the centipedegrass and St. Augustinegrass canopies was visually observed (photograph 1).…”