Temperature Factors Limiting the Spread of Cogongrass (Imperata cylindrica) and Torpedograss (Panicum repens)

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Abstract
Greenhouse, growth chamber, and field studies were conducted to determine effects of temperature on the potential of cogongrass (Imperata cylindricaL. Beauv. # IMPCY) and torpedograss (Panicum repensL. # PANRE) to spread beyond present distribution in the Lower Coastal Plains of Southeastern United States. Johnsongrass [Sorghum halepense(L.) Pers. # SORHA] was included in the study for comparative purposes. Growth of each species was greater with day/night temperature regimes of 30/25 C than with 27/22 or 24/18 C. Apical six-node-long rhizome fragments of all three species were killed by a 24-h exposure to −4.5 C. Johnsongrass produced at least three to five times more dry matter than either cogongrass or torpedograss. Order of interspecific competitiveness under 30/25, 27/22, and 24/18 C day/night temperature regimes was johnsongrass > torpedograss > cogongrass. After 2 yr, johnsongrass and torpedograss competition reduced common bermudagrass [Cyndon dactylon(L.) Pers. # CYNDA] yield by 99 and 37%, respectively, while cogongrass competition did not affect common bermudagrass yield. It is concluded that cogongrass and torpedograss are unlikely to spread into more temperate regions of the United States. However, both species are apt to become even more widespread and troublesome in the Lower Coastal Plains of Southeastern United States.