|Koger Iii, Clifford|
Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2006
Publication Date: 9/1/2006
Citation: Nandula, V.K., Eubank, T.W., Poston, D.H., Koger Iii, C.H., Reddy, K.N. 2006. Factors effecting germination of horseweed (conyza canadensis). Weed Science. 54: 898-902. Interpretive Summary: Horseweed, also known as Canada fleabane or marestail, is a troublesome weed in reduced tillage cropping systems and in no-crop areas of the continental United States. Indoor experiments were conducted to determine the influence of environmental factors on germination and emergence of horseweed. Germination of horseweed seed differed across temperature regimes, light and dark environments, soil pH ranges, and different salt concentrations. Horseweed seedling emergence was maximum on the soil surface, and no seedlings emerged from seeds placed at a depth of 0.5 cm or deeper. These results are important because they show that horseweed is able to germinate under a wide array of environmental and soil conditions, which contribute to horseweed being so prolific under a wide variety of cropping and no-crop systems.
Technical Abstract: The influence of environmental factors on germination and emergence of horseweed was examined in growth chamber experiments. Germination was highest (61%) under high (24/20 C day/night, 13 h light) temperature regime compared to 32% in the low (18/12 C day/night, 13 h light) temperature regime, or both high (15%) and low (12%) regimes under 24 h darkness. Horseweed seed germination was observed under both light (13 h photoperiod) and complete darkness (24 h), but the 13-h photoperiod was more favorable for germination than total darkness. Germination under continuous darkness was only 7-15% compared to 15-61% under light. All other experiments were conducted under the high temperature regime. Germination was 19 to 36% over a pH range from 4 to 10, with a trend towards higher germination under neutral to alkaline conditions. Horseweed germination was greater than 20% at less than 40 mM NaCl concentration and lowest (4%) at 160 mM NaCl. These data suggest that even at high soil salinity conditions, horseweed may germinate. Germination of horseweed decreased from 25% to 2% as osmotic potential increased from 0 (distilled water) to minus 0.8 MPa. Two percent germination at an osmotic potential of minus 0.8 MPa indicates that horseweed can germinate under moderate water stress conditions. Horseweed seedling emergence was maximum on the soil surface and no seedlings emerged from seeds placed at a depth of 0.5 cm or higher.