| Project Title: | Long-Term Control Programs for Redvine in Soybeans |
| Project Leaders: | David R. Shaw, John D. Byrd, Jr.,M. Alan Blaine |
| Department: | Plant & Soil Sciences |
Elkins, W. C., D. R. Shaw, J. D. Byrd, Jr., M. A. Blaine, and C. H. Tingle. 1996. Long term redvine control programs. Proc. South. Weed Sci. Soc. 49:22.
Shaw, D. R., and W. C. Elkins. 1995. Tillage and herbicide combinations for redvine control. Proc. South. Soybean Conf., P.168.
A single location with a uniform population of redvine over a 4-acre area was selected near Greenwood, MS, in 1993. The site was tilled and seedbed prepared in a normal manner in the spring of 1993. Soybeans were planted into the entire area, and Command was applied preemergence as described above. All other herbicide treatments were applied 2 weeks prior to harvest. Following harvest, all tillage treatments were accomplished as described. In the spring of 1994, Command was applied to the same plots as in 1993, and soybeans were planted across the study. In the fall, no pre-harvest herbicide or tillage treatments were repeated to determine the impact of a single herbicide-deep tillage program on long-term redvine control in subsequent years.
In the fall of 1994, a second four-acre location near Greenwood was selected to repeat the same study, since a perennial weed such as redvine can give variable results. All herbicide and tillage treatments were repeated as in 1993 at the first location.
Data collected in 1993 essentially related to the preemergence application of Command. Variability in redvine populations was observed across the experiment, which is not unusual for a perennial weedy species. Overall, Command did not have a significant i nfluence on redvine populations in the year of application when compared to respective untreated checks. However, photosynthetic rates of redvine were reduced over 30% by an application of Command. Visually this could also be observed by partial bleaching of the leaves following Command treatment.
Yields were low overall in this experiment in 1993, due to the heavy infestation of redvine in all plots. Command did not improve soybean yield in any instance.
Redvine populations in July of 1994 indicated no difference in control between Banvel or Roundup applications across all five tillage practices, and reductions were as much as 90%. Command provided little reduction in stand counts across all tillage opera tions.
Among tillage operations, subsoil with no herbicide treatment resulted in 10% redvine ground cover. The disk and paraplow with no herbicide resulted in groundcover of 36%. The chisel plow and moldboard plow resulted in groundcover of 20% when no herbicide was used. Roundup and Banvel applications resulted in groundcover of 0% to 9% in all tillage practices and no difference in groundcover reduction between the two. Groundcover reductions due to applications of Banvel or Roundup were significant in all til lage practices except for subsoil and moldboard plowed plots. Command resulted in no reduction in ground cover within each tillage practice.
Soybean yield ranged from 40 to 57 bu/A in 1994. Little effects on yield due to herbicide applications or tillage practices occurred. Soybean moisture levels ranged from 11% to 13% moisture, within the recommended range of moisture percent at harvest. Moi sture levels of 11% were found with moldboard plow alone or in combination with Banvel at 2.0 lb ai/A. Chisel plow alone or with Command at 1.0 lb ai/A resulted in moisture levels of 13%.
In 1995, the percentage of redvine cover just prior to harvest was 14% and 19% with the moldboard plow and paraplow operations, respectively, with no herbicide treatment. The disk with no herbicide had a redvine groundcover of 38%. The chisel plow and sub soil operation resulted in groundcover levels of 28% and 25%, respectively, when no herbicide was used. No treatment with Roundup or Banvel had redvine groundcover above 6%, which was a significant reduction from the untreated plots in all tillage operati ons. Command failed to reduce groundcover in all tillage operations.
Stem count data reflects similar trends as percent groundcover. With the use of Banvel or Roundup, regardless of tillage operation, stem counts were 1505 stems/ha or less, compared to 20056 stems/ha in the disk without herbicide treatment.
Comparison of data from an identical study begun in 1993 indicates patterns much like the 1994-1995 study. Tillage operations and herbicide application for this study were completed in the fall of 1993, with Command applied spring 1993 and each following year at planting. Roundup and Banvel applications in all tillage treatments resulted in groundcover of 1% to 10% in 1995, two years after application. Groundcover reductions (from disked check) were significant in all tillage operations except for subsoil . Repeated application of Command for three growing seasons did not reduce redvine groundcover.
In 1996, plots were maintained and soybeans were planted in both studies on June 20. This late planting date was due to extremely dry weather for the 45 days prior to that time. Redvine groundcover in the study established in 1993 (C96-51) indicated that Roundup and Banvel, the best herbicide programs overall, were not maintaining control in the Disk treatments the third year after application. However, reductions were noted following these treatments when the soil had been moldboard plowed, subsoiled or chisel plowed. Command continued to cause no reductions in redvine populations or groundcover after 4 years of continuous applications in soybeans. In the untreated checks, the subsoiling reduced redvine groundcover compared to most of the other tillage t reatments. Thus, substantial differences are beginning to arise in both herbicide-treated and untreated plots between tillage systems.
In the study established in 1994 (C96-52), no differences were noted in redvine groundcover when comparing an individual herbicide treatment to its untreated check within a tillage system. However, this lack of differences was partially due to significant differences in groundcover between untreated checks, i.e., the tillage treatments were affecting redvine populations. Combining moldboard plowing with a Roundup or Banvel application resulted in redvine groundcover of less than 6% 2.5 years after applica tion.
Soybean yields were measured from both studies. However, yields were low overall due to the late planting date and late harvest date. Soybeans were late in maturing and, as a result of the high rainfall on these heavy clay soils in October through Decembe r, plots were ultimately hand-harvested the week before Christmas. Very few significant differences occurred between treatments. This is not surprising, in that the deep-rooted perennial nature of redvine results in very little competition.
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