Full TGIF Record # 65965
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Publication Type:
i
Report
Content Type:Abstract or Summary only
Author(s):Waltz, Aaron L.; Martin, Alex R.; Roeth, Fred W.; Lindquist, John L.
Author Affiliation:Waltz: Research Assistant; Martin and Roeth: Professors; Lindquist: Assistant Professor, Department of Agronomy, University of Nebraska, Lincoln, NE
Title:Glyphosate efficacy with varying time of day applications
Meeting Info.:Columbus, OH: December 14-16, 1999
Source:Proceedings of the North Central Weed Science Society. Vol. 54, 1999, p. 141-142.
# of Pages:2
Publishing Information:Champaign, IL: North Central Weed Science Society
Keywords:TIC Keywords: Glyphosate; Herbicide evaluation; Time-of-day; Application timing; Weed control; Agriculture; Application rates; Biomass; Dry weight; Herbicide injury; Photosynthesis; Transpiration; Stomatal conductance; Environmental factors; Humidity
Abstract/Contents:"The widespread use of herbicide-resistant crops has led to the increased use of glyphosate. The portion of U.S. soybeans treated with glyphosate increased from 25% in 1996 to 46% in 1998. Increased use of glyphosate has given rise to several observations. One of these observations is that weed control with glyphosate may be affected by the time of day that an application is made. This study was implemented to examine this possible time of day effect on weed control with glyphosate. Velvetleaf was chosen as the subject weed because of its economic importance in agricultural fields and its widespread germination window for repeated studies throughout a summer. An experiment was designed as a split-plot randomized complete block with a factorial arrangement of treatments. The plots were split with time to control the effect of possible drift damage. The experiment was conducted three times during the summer of 1999: July 8, August 12, and September 1. Time was the main factor with five or seven levels depending on the experimental day. The day was normalized from 0 (sunrise) to 1 (sunset) with applications made at -0.1, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.1 of the normalized day. The normalization was done to adjust for the change of daylight at each date. There were four rates of glyphosate as well as a weedy control for each main plot. The rates of glyphosate included 0.28 kg ai/ha, 0.56 kg ai/ha, 0.84 kg ai/ha, and 1.12 kg ai/ha. Velvetleaf was planted monoculture in 76 cm rows and thinned to 20 plants/3 m row in one row of each plot. Variables mesaured include freshweight biomass, dryweight biomass, injury (scale from 1 to 10, 1 being no injury, 10 being no green plant material), and percent mortality (number of dead plants out of 20 then multiplied by 100). An automated weather data network weather station was used to measure climatological variables such as air temperature, wind speed, and relative humidity. The Li-Cor 6200 Leaf Photosynthesis System was used to measure physiological plant variables such as photosynthesis, transpiration, and stomatal conductance. There is evidence that the time of day glyphosate is applied does have an effect on velvetleaf control. Each experimental date showed slightly different relationships between time of glyphosate application and weed control (as determined by percent mortality), however, in all cases, an application made later in the day was better with respect to weed control than an application before sunrise or an early morning application. On August 8 at the 0.56 kg ai/ha rate, percent mortality was 10, 45, 90, 95, 93, 95 and 65% at -0.1, 0.1, 0.3, 0.5, 0.7, and 0.9 [and 1.1], respectively. Similar trends were seen with fresh weight biomass, dry weight biomass, and injury data. Each rate was studied separately and the relationship between rates was different. In all cases, the 0.28 kg ai/ha application was least effective in weed control and varied little throughout the day. On two of the three provided nearly 100% control at all application times. On August 8, however, the applications made before sunrise showed poor velvetleaf control. The next important step is to examine what is the main driving force behind this time of day effect. Investigating velvetleaf control at one rate for one of the experimental days shows a positive correlation with air temperature and a negative correlation with relative humidity. Relative humidity may not be the driving force in this case since the weed control was highest at low relative humidity (40%) and lowest at high relative humidity (95%). Another correlation was evident between weed control and photosynthetic rate, suggesting that control may be somewhat dependent upon the activity level of the plant during application. These relationships require further study and examination to determine what is causing the time of day effect with glyphosate applications."
Language:English
References:0
Note:This item is an abstract only!
ASA/CSSA/SSSA Citation (Crop Science-Like - may be incomplete):
Waltz, A. L., A. R. Martin, F. W. Roeth, and J. L. Lindquist. 1999. Glyphosate efficacy with varying time of day applications. Proc. North Cent. Weed Sci. Soc. 54:p. 141-142.
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