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Cogongrass: Biology and Impacts

Cogongrass: Biology and Impacts. Greg MacDonald University of Florida. Introduction. Native to southeast Asia Infests nearly 500 million acres worldwide Found on every continent Except Antarctica Tropical and subtropical areas, limited spread to northern temperate regions

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Cogongrass: Biology and Impacts

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  1. Cogongrass: Biology and Impacts Greg MacDonald University of Florida

  2. Introduction • Native to southeast Asia • Infests nearly 500 million acres worldwide • Found on every continent • Except Antarctica • Tropical and subtropical areas, limited spread to northern temperate regions • Considered to be one of the worst weeds

  3. Introduction to U.S. • First appearance • Grand Bay, Alabama • Escape from crate packing in 1912 • Intentional introduction • Mississippi as a possible forage in 1921 • Florida introduction 1930s and 1940s • However, little economic (forage) benefit

  4. Cogongrass infestation in the southeastern United States points of introduction

  5. Adaptation • Highly adapted to poor soils • Ability to survive low nitrogen, phosophorus • Prefers low pH soils with low organic matter • Extremely drought tolerant through specialized rhizome features • Unique photosynthetic mechanism • C4 photosynthesis • Adapted to low light environments (<5% sun)

  6. Pyrogenic • Fire-based species • Accumulates excess leaves for fire • Burns hotter (15-20 C) than normal understory fires • Eliminates trees, shrubs, other forbs – maintains dominance

  7. Cogongrass Biology • Grows in loose to compact bunches, containing several leaves • Leaves arise from a central area along a rhizome • Originate directly from ground level

  8. Leaves • 1-4 feet in length, ½ to ¾ inch wide • Prominent, off-center, white mid-rib • Margins are finely serrated, accumulate silicates

  9. Seed Production • Predominately in the spring • Long, fluffy-white seedheads • Mowing, burning or fertilization may induce seedhead formation

  10. Seeds • Extremely small • Attached to a plume of long hairs • May be carried long distances by wind or humans • Over 3000 produced per plant • Relatively short lived, < 1 year

  11. Rhizomes • Comprise over 60% of total biomass • 40 tons per acre • Penetrate soil to a depth of 4 feet, but most found in the top 6 to 10 inches

  12. Rhizomes • Rapid regenerative capacity • Central core to resist breakage and drought tolerance • Scale leaves surround each bud

  13. Rhizomes • Multiple buds per rhizome section • Apical dominance maintains dormancy • Evidence of additional dormancy mechanisms

  14. Allelopathy • Rhizomes exude substances that retard the growth of other plants • Increasing cogongrass density excludes other vegetation

  15. Varieties of Cogongrass? • Var. major • Var. europa • Var. africana • Var. condensata • Var. latifolia • Imperata brasiliensis – Brazilian satintail

  16. var. ‘Rubra’ • Red variety of cogongrass • Sold widely in the ornamental trade • Red Baron, Japanese Blood Grass

  17. ‘Rubra’ • Will revert to the normal green biotype • Conflicting reports on aggressiveness • Appears to be cold-tolerant • Genetically related to I. brasiliensis??

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