Full TGIF Record # 16329
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Web URL(s):http://www.wsweedscience.org//wp-content/uploads/proceedings-archive/1989.pdf#page=230
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Author(s):Mueller-Warrant, G. W.
Author Affiliation:USDA-ARS, National Forage Seed Prod. Res. Center, Corvallis, OR
Title:Influence of Temperature on Response of Roughstalk Bluegrass to Fenoxaprop.
Meeting Info.:Held March 13-16, 1989, Honolulu, HI.
Source:Proceedings of the Western Society of Weed Science. Vol. 42, March 1989, p. 218-220.
Publishing Information:Logan, UT: Plant Science Dept., Utah State University.
Keywords:TIC Keywords: Temperatures; Fenoxaprop-ethyl; Poa trivialis; Avena fatua; Lolium perenne; Application timing; Age; Weed control; Seedlings; Growth rate; Metabolism; Germination; Growth chambers; Herbicide application; Regrowth; Susceptibility; Survival
Abstract/Contents:"Fenoxaprop {(+/-)-2-[4-[(6-chloro-2-benzoxazoly)oxy]phenoxy]propanoic acid} was recently registered for control of roughstalk bluegrass (Poa trivialis) and wild oats (Avena fatua) in perennial ryegrass (Lolium perenne) grown for seed in Oregon. Control of roughstalk bluegrass in field trials varied substantially with timing of application and age of the weed, with seedlings being more easily controlled than older, more well-established plants. Sensitivity of perennial ryegrass also varied with date of application during the fall through the spring growing season, with greatest injury coming from treatments applied in April. Roughstalk bluegrass control was poor in the fall, satisfactory in late winter, but usually best in early spring. Optimum date of application was around March 1 in 1987, a year with a warmer than normal winter and around April 1 in 1988, a more normal winter. Since weather follows a general warming trend during late winter and early spring, it seemed probable that the temperature near time of treatment was a major factor in the response of these two species to fenoxaprop. However, since temperature influences growth rate of grasses, causing changes in size over time, response to fenoxaprop applied in the field at different dates included confounded effects of differing plant sizes and rates of metabolism. Tests were therefore conducted in growth chambers to more precisely define effects of temperature on the response of roughstalk bluegrass to fenoxaprop. Roughstalk bluegrass was germinated in a greenhouse under 16 C day/10 C night, 12-hr photoperiod conditions. Seedlings were thinned to a final density of 3 weeds per pot at 25 days after germination, and moved into growth chambers 3 days later. Growth chamber conditions were 12 hr light/12 hr dark photo periods, with a dark period temperature of 2 C in all chambers. Plants were grown in the light period at 5, 8, 11, and 14 C for 22 days prior to herbicide treatment. After herbicide treatment, plants were returned to growth chambers for 36 days before they were harvested for above ground fresh-weight yield. Following this harvest, the plants were allowed to regrow in the greenhouse for 17 days, after which time percent mortality was evaluated based on failure to regrow. The experiment was arranged as a complete factorial with four pre-treatment temperature regimes, four post-treatment temperature regimes, six rates of fenoxaprop (0, 56, 112, 168, 224, and 280 g ai/ha), and six replications within chambers. Susceptibility of roughstalk bluegrass to fenoxaprop was inversely related to pre-application temperature and directly related to post-application temperature. Since size of the weed at treatment increased with pre-application temperature, the effect of pre-application temperature can be explained as a decrease in susceptibility in larger plants. Reduction in roughstalk bluegrass growth caused by application of any rate of fenoxaprop was proportional to post-treatment temperature within the range tested from 5 to 14 C. Similar conclusions can be drawn from weed mortality evaluations based on failure to regrow after the fresh-weight harvest. Differences in survival disappeared at higher rates due to death of all plants. The growth chamber results suggest that fenoxaprop was most effective when applied to actively growing grass, which agrees with findings by other workers for other grasses. Similar control from equal rates of fenoxaprop was achieved for pre- and post-treatment temperature combinations of 4/8, 8/11, and 11/14 C. This result seems to indicate that, within this range of temperatures, delaying application for a few weeks during a period of continuously increasing temperature would have little, if any, net effect on performance of fenoxaprop. Larger plants present at later dates of treatment would be proportionately more sensitive due to their faster growth rates under the warmer conditions following treatment. However, if a general warming trend were broken by a period of cooler weather soon after treatment, herbicide performance might decline with delay in application date. Conversely, performance of fenoxaprop applied too early might be impaired by coolness of the weather at that time if an anticipated warming trend failed to materialize."
ASA/CSSA/SSSA Citation (Crop Science-Like - may be incomplete):
Mueller-Warrant, G. W. 1989. Influence of Temperature on Response of Roughstalk Bluegrass to Fenoxaprop.. Proc. West. Soc. Weed Sci. 42:p. 218-220.
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