ARS | Publication request: SIMULATION OF SHOOT EMERGENCE PATTERN OF COGONGRASS (IMPERATA CYLINDRICA) IN THE HUMID TROPICS

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 18, 2004
Publication Date: November 4, 2004
Citation: Ekeleme, F., Forcella, F., Archer, D.W., Chikoye, D., Akobundu, I.O. 2004. Simulation of shoot emergence pattern of cogongrass (Imperata Cylindrica) in the humid tropics. Weed Science. 52:961-967.

Interpretive Summary: Cogongrass is a perennial grass that has invaded many countries in the tropical and subtropical regions of the world. Its management has been challenging because it can regenerate itself from rhizome buds in the soil. The emergence pattern of this weed under field conditions has received little attention. Field trials were conducted in 2002 and 2003 in the humid forest zone of southeastern Nigeria. Information from these trials allowed us to construct a computer model that predicts the timing and extent of shoot emergence. The development of the model was based on hydrothermal time, which represents the amount of time at which both soil water and soil temperature at the 1" depth are above lower limits of growth for a particular plant species. A type of equation, called a Weibull function (basically, an S-shaped curve), was used to describe the relationship between hydrothermal time and shoot emergence. The model was evaluated against shoot emergence in southwestern Nigeria, where it predicted shoot emergence quite well. This is the first model of cogongrass shoot emergence based on hydrothermal time and developed using field observations. The primary beneficiaries of this research are other scientists and extension educators. The research helps to set a stage for further analyses of emergence patterns and the best times for cogongrass management.

Technical Abstract: Cogongrass is a noxious perennial grass that has invaded many countries in the tropical and subtropical regions of the world. Its management has been a significant challenge because of large rhizome and bud reserves in the soil. The emergence pattern of this weed under field conditions has received little attention. Field trials were conducted in 2002 and 2003 in the humid forest zone of southeastern Nigeria to model shoot emergence. The experiment had four treatments: (1) count and tag intact shoots, (2) count and kill shoots with paraquat, (3) count and kill shoots by cutting, and (4) count and cut shoots in field corn. The rationale for these treatments was to check the effect of different monitoring techniques on shoot emergence of cogongrass. The development of the model was based on hydrothermal time, which was calculated from soil moisture and soil temperature at 2 cm depth. A Weibull function was fitted to cumulative percentage shoot emergence values of treatment 4 and hydrothermal time. The model described cogongrass shoot emergence well (r**2 = 0.95, n = 36). The model was evaluated against shoot emergence from six treatments that simulated farmers' practices in southwestern Nigeria, wherein it predicted shoot emergence adequately (r**2 > 85, P < 0.001, n = 6 in each treatment). This is the first model of cogongrass shoot emergence based on hydrothermal time and developed using field observations. The model helps to set a stage for further analysis of emergence patterns and timing of cogongrass management.