Progress 10/01/07 to 06/30/11
Outputs
OUTPUTS: The early focus of this project was primarily weed/crop interference to determine crop yield reductions and establish economic thresholds in various crops. This entailed examining the biology/ecology interactions of weeds and crops. Knowledge of weed interactions with crops allows weed scientists to determine effective weed management programs that could decrease crop yield loss, often with less herbicide usage. Timing of planting to give crops a competitive advantage over weeds was another tactic studied. Growth analysis of weed accessions from across Arkansas and the mid-South helped determine optimal timing of herbicide applications for various cropping areas. As weed resistance has evolved, these analyses have provided data for modeling resistance evolution. Because of increasing weed resistance, especially resistance to glyphosate, which is used widely in many crops, our effort became focused on integration of weed biology/ecology principles into resistance management programs. Accordingly, work in this project included a study of biological differences among Palmer amaranth (Amaranthus palmeri) and pitted morningglory (Ipomoea lacunosa) accessions and the extent to which genetic diversity could explain differences. With increasing weed resistance, weed science research is focusing more on a longer-term approach to weed management than simply that of current-season economic thresholds that of preventing evolution, spread, and reproduction of weeds that are or could become resistant. One of the major tenants of effective resistance-management programs is reducing seed input into the soil seedbank, thereby reducing the number of potentially resistant weed ecotypes. Studies were conducted to determine the effects of late-season glyphosate applications on the density and seed production on several weed species, including Palmer amaranth, pitted morningglory, entireleaf morningglory (Ipomoea herderacea var. integriuscula), prickly sida (Sida spinosa), broadleaf signalgrass (Urochloa platyphylla), sicklepod (Senna obtusifolia), and barnyardgrass (Echinochloa crus-galli). Diclofop-resistant Italian ryegrass has also received attention for development of sound control practices. Conclusions from these biology/ecology studies are shared with extension weed scientists, whose goal is to increase producer and consultant awareness of the impacts of biology and ecology on weed management programs. In many cases, alternative management programs can be devised that use weed biology as a basis for weed control. The justification, goals, and preliminary results of the project have been shared with producers, consultants, weed scientists, and industry personnel through experiment station field days and local and regional meetings such as the Arkansas Crop Protection Association, Delta Weed-Workers Informal Get-Together, Southern Weed Science Society, and Weed Science Society of America. Data on Palmer amaranth in the seedbank has been used in the glyphosate-resistant Palmer amaranth computer model, and data from evaluation of other weeds can be included in future management models. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
This project has provided information from which efficient weed management programs have been developed by integrating cultural methods of control based on weed biology/ecology principles. For example, we found that manipulation of soybean populations to increase their interference potential with weeds resulted in reduced herbicide inputs. Timing of planting to give crops a competitive advantage over weeds was another successful tactic studied. Arkansas university and extension service weed scientists have a strong, cooperative relationship, which has allowed the use of weed biology/ecology strategies in weed management to be quickly recommended to producers. For several decades, consultants and producers have counted on economic weed thresholds for determining when weeds must be controlled to prevent significant yield loss from weed interference. Much of the data used to establish thresholds was generated from work in this project. In the last decade, producers have faced the increasing evolution of herbicide-resistant weeds, so project efforts were concentrated on the interaction of crops and resistant weeds to mitigate resistance issues. Because of knowledge of weed biology, resistance management recommendations to producers could be quickly focused on long-term management rather than management for economic thresholds. A computer model developed for managing glyphosate-resistant Palmer amaranth emphasized the importance of controlling the weed soil seedbank to mitigate spread of resistant species. We showed that multiple applications of glyphosate, with one applied at weed flowering and followed by sequential application at 10 to 30 days after flowering reduced weed seed production 90 to 100% each year by preventing seed from developing viable embryos. After 3 years, the emerging non-glyphosate-resistant weed population was reduced 98% or more from the original infestation. The importance of weed densities and seed production is reflected in the computer model for glyphosate-resistant Palmer amaranth and in educational materials on resistant weeds developed by Arkansas weed specialists. This knowledge will allow use of glyphosate as a seed-reduction strategy and will be of value for crop producers in the mid-South to plan economical, sustainable resistance-management strategies. The integration of cultural control methods into weed management strategies may also be of economic benefit to Arkansas and mid-South crop producers.
Publications
- Bararpour, M., D. Oliver, and C. Bell. 2011. Comparison of HPPD inhibitors for weed control programs in corn. Proc. South. Weed Sci. Soc. 64:265.
- Bararpour, M. and D. Oliver. 2011. Effect of Roundup-Ready technology on weed population dynamics in soybean. Proc. South Weed Sci. Soc. 64:267.
- Bell, C. G. 2011. Weed control and economic evaluation in glyphosate-, glufosinate-, glyphosate acetyl transferase-resistant, and conventional soybean. M.S. thesis. University of Arkansas, Fayetteville. 104 pp.
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Progress 01/01/10 to 12/31/10
Outputs
OUTPUTS: Successful weed management programs depend on principles of weed biology and ecology. With the increasing need to develop weed management programs for herbicide-resistant weeds, there is also an increasing need to focus effort on the soil seedbank. Weed scientists have become aware that managing the soil seedbank is necessary to economical, sustainable crop production. A computer model, developed by a cooperative effort of Arkansas and UKweed scientists, for evaluating and recommending management strategies for glyphosate-resistant Palmer amaranth has shown the need for controlling weed seed production as part of a weed management program to mitigate resistance. In 2010, research continued to evaluate the effects of glyphosate technology (Roundup Ready) on the density and seed production of Palmer amaranth, pitted morningglory (Ipomoea lacunosa), entireleaf morningglory (Ipomoea herderacea var. integriuscula), prickly sida (Sida spinosa), broadleaf signalgrass (Urochloa platyphylla), and barnyardgrass (Echinochloa crus-galli). Glyphosate treatments were applied at different timings, and weed emergence was measured throughout the season. This research has been shared with extension weed scientists, who are increasing producer and consultants' awareness of the need for knowledge of the soil seedbank as a consideration for future weed management strategies and as a way of mitigating herbicide resistance. In searching for alternatives for managing glyphosate-resistant Palmer amaranth, glufosinate (Ignite) was evaluated in Liberty Link soybean to begin to determine if there will be a benefit to the soil seedbank. Another project that continued into 2010 is the development of early switchgrass establishment and control of weeds in switchgrass, a plant of interest as a potential biofuel crop. The justification, goals, and preliminary results of the project have been shared with producers, consultants, and industry personnel who attended experiment station field days and requested individual farm visits. Data were presented at the annual meeting of the Arkansas Crop Protection Association held in November. Data on Palmer amaranth in the seedbank can be used in the glyphosate-resistant Palmer amaranth computer model, and data from evaluation of other weeds can be included in future management PARTICIPANTS: Cooperative work on resistant weed populations is with Arkansas weed scientists Drs. Jason Norsworthy, Nilda Burgos, Bob Scott, and Ken Smith. A cooperator in the switchgrass work is Dr. Chuck West, with expertise in forage grasses. TARGET AUDIENCES: The target audience for this project is the Arkansas crop producer. With the increasing problem of herbicide-resistant weeds, it is important that producers understand the long-term effects of the soil seedbank and ways to reduce seed deposition. Arkansas weed scientists are experienced in getting appropriate research results promptly to producers through research and extension educational programs. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
With increasing incidences of herbicide-resistant weeds, it is important to consider management of weeds from the perspective of future crops as well as the present-year crop. The soil seedbank, therefore, must be considered. This project results in information that can be used immediately and with future crops in mind, such as programs to control density of the weed population, thereby reducing deposition of seeds to the soil to reduce future problems. The project showed that glyphosate technology can drastically reduce the addition of weed seed to the soil seedbank when glyphosate is used in weed management programs that prevent season-long emergence. After 3 years, the emerging non-glyphosate-resistant weed population was reduced 98% or more from the original infestation. The importance of weed densities and seed production is reflected in the computer model for glyphosate-resistant Palmer amaranth and in educational materials on resistant weeds developed by Arkansas weed specialists. This knowledge will allow use of glyphosate as a seed-reduction strategy and will be of value for crop producers in the mid-South to plan sustainable management strategies. For producers interested in the potential of switchgrass as a biofuel, weed management programs are being established as a result of this project.
Publications
- Burgos, N.R., Tseng, T.M., Shivrain, V.K., Sales, M.A., Alcober, E.A., Oliver, L.R. and. Scott, R.C. 2009. ACCase mutation profile of herbicide-resistant ryegrass in Arkansas. Vol. 49. Accessible at http://wssa.net/Meetings/WSSAAbstracts.
- Bell, C.G. and Oliver, L.R.. 2010. Weed control programs in soybean. Proc. South. Weed Sci. Soc. 63:6.
- Bararpour, M.T., Oliver, L.R. and Bell, C.G. 2010. Initial evaluation of Optimum GAT (glyphosate/ALS tolerance) technology in corn and soybean. Proc. South. Weed Sci. Soc. 63:120.
- Bell, C., Oliver, L.R. and Bararpour, M.T. 2010. Weed control programs in soybean. Abstr. AR Crop Prot. Assoc. 14:14-15.
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Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: Successful weed management programs depend on principles of weed biology and ecology. Consultants and producers have counted on economic weed thresholds for determining when weeds must be controlled to prevent significant yield loss from weed interference. However, with the costs of weed control rising and the need to manage for herbicide-resistant weeds increases, we believe that some weed management attention should also focus on the soil seedbank. We have seen how an infestation of glyphosate-resistant Palmer amaranth (Amaranthus palmeri) can evolve from a single small patch in a field to a major problem that may even require abandonment of the crop. Weed scientists have become aware that managing the soil seedbank is necessary to economical sustainable crop production. A computer model, developed by a cooperative effort of Arkansas and Australian weed scientists, for evaluating and recommending management strategies for glyphosate-resistant Palmer amaranth has shown the need for controlling weed seed production as part of a weed management program to mitigate resistance. In 2009, research was conducted for the third year to evaluate the effects on late-season glyphosate applications on the density and seed production of Palmer amaranth, pitted morningglory (Ipomoea lacunosa), entireleaf morningglory (Ipomoea herderacea var. integriuscula), prickly sida (Sida spinosa), broadleaf signalgrass (Urochloa platyphylla), and barnyardgrass (Echinochloa crus-galli). Glyphosate treatments ranged from a single application at the soybean V3 growth stage to applications at V3 followed by applications at V6, weed flowering, and 10-day sequential applications after weed flowering. This research has been shared with our extension weed scientists, who are also interested in increasing producer and consultants' awareness of the need for knowledge of the soil seedbank as a consideration for future weed management strategies and as a way of mitigating herbicide resistance. The justification, goals, and preliminary results of the project have been shared with producers, consultants, and industry personnel who attended experiment station field days. Data were presented at the annual meeting of the Arkansas Crop Protection Association held in November. Data on Palmer amaranth in the seedbank can be used in the glyphosate-resistant Palmer amaranth computer model, and data from evaluation of other weeds can be included in future management models. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Although most producers are not yet aware of the importance of considering the effects of their weed management programs on the soil seedbank, we believe awareness should and can be enhanced through educational materials presented by university scientists and extension service personnel, experiment station field days, and weed management models for specific weed problems. Because of the potential for site-specific management, it will perhaps be easier to consider management of weeds from the perspective of future crops as well as the present-year crop. This study showed that the glyphosate technology can drastically reduce the addition of weed seed to the soil seedbank. Results indicated that multiple glyphosate applications, with one applied at 0.42 kg ae/ha at weed flowering followed by a sequential application at 10 to 30 days after flowering reduced weed seed production 90 to 100% each year. At the end of 3 years, the emerging weed population was reduced 98% or more from the original infestation. The application at weed flowering (triggered by barnyardgrass one year and Palmer amaranth two years as the first species to flower) prevented seed from developing viable embryos (often referred to as 'blanking' seed production). This knowledge will allow use of glyphosate as a seed-reduction strategy and will be of value for crop producers in the mid-South to plan sustainable management strategies.
Publications
- Barapour, M.T. and Oliver, L.R. (2009). Effect of Roundup-Ready technology on weed population dynamics in soybean. In R.C. Scott editor. Abstr. Arkansas Crop Protection Association. Nov.1-Dec.1, 2009. Fayetteville, AR. p.13.
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: Principles of weed biology and ecology can be used to determine successful weed management programs in most crops. Interference studies of many weeds over the years show the importance of controlling weeds early, while they are still small. Cost of weed control is perhaps more important than ever. Rising input cost for soybean production is a major constraint for Arkansas producers. Thus, lowering fuel, seed, and herbicide cost can influence a producer's profit margin. Conventional soybean varieties can reduce cost by avoiding technology fees associated with Roundup Ready varieties, and early-maturing varieties can reduce irrigation cost. Planting any of these varieties at high populations can also reduce herbicide cost due to earlier canopy closure. Research was conducted to determine the influence of soybean maturity group (MG), soybean plant density, and herbicide program on soybean yield and weed management costs. Although there was a special interest in ultra-early maturity group (MG) soybean, under conditions at the test locations, yield and profit for MG IV soybean planted at 200,000 seed/A and treated with either a conventional or Roundup Ready herbicide program was generally better than MG II and III planted at 125,000 or 75,000 seed/A. Work with weed seed production as influenced by glyphosate applied at flowering showed that, although glyphosate applied every 10 d was more effective than single applications, the single application of 0.75 lb/A was most practical and reduced seed production of a number of species by 88 to 99%. Translocation of glyphosate in one of those weed species, sicklepod (Senna obtusifolia), caused bud and flower abscission, which reduced sicklepod seed production. Hoelon-resistant Italian ryegrass is a problem in Arkansas wheat. Although differences in control can be seen with different herbicide programs, split herbicide applications control the resistant biotypes better than do single applications. Tillage level, however, did not influence Italian ryegrass control. Because one of the most severe weed problems in several decades is glyphosate-resistant Palmer amaranth, plans are being made to study its biology and ecology to determine mechanisms of spread, seed production and dispersal, and interference potential. This information is needed for input to a Palmer amaranth model that can predict how rapidly resistance can occur under certain conditions and how management programs, including seed production programs, can affect evolution of resistance. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Because site-specific management is increasingly playing a role in weed management programs, rate of weed development, effects of timing of crop planting, interference potential of the increasing number of herbicide-resistant weeds, and effects of cultural practices need to be determined to provide optimal weed control and crop yield at a low cost. The results of this project contribute to the awareness of producers of the value of an integrated weed management program for sustainable and economical weed control.
Publications
- Lyons, F.H., Oliver, L.R., Purcell, L.C., and Popp, M.P. 2008. Profitable systems for ultra-early soybean production. Proc. South. Weed Sci. Soc. 61:6.
- Norsworthy, J.K., Giffith, G.M., Scott, R.C., Smith, K.L., and Oliver, L.R. 2008. Confirmation and control of glyphsoate-resistant Palmer amanranth. Weed Technol. 22:108-113.
- Walker, E.R. and Oliver, L.R. 2008. Weed seed production as influenced by glyphosate-applications at flowering across a weed species. Weed Technol. 22:318-325.
- Walker, E.R. and Oliver, L.R. 2008.Translocation and absorption of glyphosate in flowering sicklepod (Senna obtusifolia). Weed Sci. 56:338-343.Bararpour, M.T., Oliver, L.R., and Lyons, F.H. 2008. Hoelon-resistant Italian ryegrass control with pinoxaden (Axial).
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Progress 01/01/07 to 12/31/07
Outputs
As more societal emphasis is placed on sustainability and 'going green,' an understanding of weed biology and crop-weed ecology is gaining importance as a way of managing weeds using practices based on these principles. Weed management is most effective if weeds are controlled early when they are less competitive. Therefore, experiments have been conducted to determine emergence patterns of 76 weed species common to Arkansas. Emergence of annual grass species was from early April to early May. Broadleaf and perennial species emerged from April to mid-June. Duration of emergence during the season also differed among weed species, and species were classified as having quasi-simultaneous or short- or long-season continuous emergence. These data can aid in decisions about when to plant crops to avoid the worst infestations. Weed development rates, as calculated by growing degree days (GDD), can be used in crop management models to allow producers to make the most timely
herbicide applications for maximum weed control in their fields. GDD can also be used to predict flower initiation for timely glyphosate applications to reduce seed input into the soil seedbank. Interference potential of a glyphosate-resistant common ragweed ecotype was greater than that of the susceptible ecotype, emphasizing the importance of control early in the growing season to prevent significant soybean yield loss. By studying germination and viability following maturity on the mother plant, some predictions can be made as to the degree of contribution of certain weeds to the soil seedbank. For example, sicklepod seed from plants emerging earlier in the season and at lower fruiting positions had greater dormancy than late-season plants and seed from high fruiting position. Information from these studies forms the basis for designing experiments to test weed management systems developed from principles of crop-weed ecology, giving producers in the mid-South more alternatives for
weed control.
Impacts
Characterizing variability within a weed species is a cornerstone of site-specific management, which is increasingly playing a role in pest management. Emergence of annual grass species was from early April to early May. Broadleaf and perennial species emerged from April to mid-June. Predictive information on rate of weed development will allow producers to make the most timely herbicide applications for maximum control in their fields. Growing degree day (GDD) data also allows modeling of time(s) of emergence and growth and development of weed species common to crop production and enables cultural management practices to be devised that take advantage of weed/crop ecology and to reduce seed input into the soil seedbank. The importance of greater competitive potential in glyphosate-resistant common ragweed than in the susceptible ecotype alerts producers that the resistant ecotype should be controlled earlier than the susceptible one. Producers receive results of these
studies through recommendations for managing a particular crop and weed spectrum with cultural practices designed to increase economic benefits and, in some cases, to reduce herbicide use. A secondary benefit of this research is that it provides training in weed biology/ecology for students who will one day be in jobs in which they are responsible for weed management recommendations.
Publications
- Alford, J.L. 2007. Emergence patterns, growth, and seed viability of selected weeds. PhD dissertation. University of Arkansas, Fayetteville. 131 pp.
- Brewer, C.E. 2007. Arkansas glyphosate-resistant common ragweed (Ambrosia artemisiifolia). PhD dissertation. University of Arkansas, Fayetteville. 87 pp.
- Brewer, C.E. and Oliver, L.R. 2007. Reducing weed seed rain with late-season glyphosate applications. Weed Technol. 21:753-758.
- Lyons, F.H., Oliver, L.R., Purcell, L.C., and Popp., M.P. 2007. Profitable systems for ultra-early soybean production. Abstr. Ark. Crop Prot. Assoc. 11:7-8.
- Walker, E.R. and Oliver, L.R. 2007. Translocation and absorption of glyphosate in flowering sicklepod (Senna obtusifolia). Weed Sci. (accepted).
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Progress 01/01/06 to 12/31/06
Outputs
Weed management and crop sustainability can be improved with practices based on principles of crop-weed ecology. Weed management is most effective if weeds are controlled early when they are less competitive. Weed development rates, as calculated by growing degree days (GDD), can be used in crop management models to predict timely and precise herbicide applications. GDD can also be used to predict flower initiation for timely glyphosate applications to reduce seed input into the soil seedbank. GDD were calculated for five weed species. From cotyledon to flowering, GDD were 652 for broadleaf signalgrass (Brachiaria platyphylla), 326 for hemp sesbania (Sesbania exaltata), 469 for sicklepod (Senna obtusifolia), 451 for prickly sida (Sida spinosa), and 917 for velvetleaf (Abutilon theophrasti). Broadleaf signalgrass and hemp sesbania were fastest to develop from the cotyledon to the four-leaf stage. GDD measurements allow producers to predict weed development, thereby
providing knowledge of when to expect weeds to develop to a given stage and making the most timely herbicide applications for maximum weed control in their fields. The discovery of glyphosate-resistant common ragweed (Ambrosia artemisiifolia) in Arkansas created a need for determining yield loss of soybean based on full-season interference. Interference potentials were evaluated for a glyphosate-resistant and a susceptible ecotype. Common ragweed interference in soybean indicated that one resistant plant per row foot caused a 28% yield reduction, but three of the susceptible plants were needed to cause a similar yield reduction. Comparative growth analysis indicated that the resistant ecotype attained 18% more biomass, was 16% taller, and had 32% more leaf area than the susceptible ecotype when averaged over harvest intervals of 2 to 8 weeks after emergence. Photosynthetic efficiency was not different between ecotypes, and leaf area ratio indicated that more resources were invested
into leaf production in the resistant plants than the susceptible. The more competitive glyphosate-resistant common ragweed must be controlled early in the growing season to prevent significant soybean loss.
Impacts
Characterizing variability within a weed species is a cornerstone of site-specific management, which is increasingly playing a role in pest management. Predictive information on rate of weed development will allow producers to make the most timely herbicide applications for maximum control in their fields. The importance of greater competitive potential in glyphosate-resistant common ragweed than in the susceptible ecotype alerts producers that the resistant ecotype should be controlled earlier than the susceptible one.
Publications
- Alford, J.L. and Oliver L.R. 2006. Determining weed development using photothermal days. Abstr. Weed Sci. Soc. Am. 46:39.
- Alford, J.L. and Oliver, L.R. 2006. Seed germination and viability effects in response to growth hormones and herbicides. Proc. South. Weed Sci. Soc. 59:181.
- Bond, J.A., Oliver, L.R., and Stephenson, D.O. 2006. Response of Palmer amaranth (Amaranthus palmeri) accessions to glyphosate, fomesafen, and pyrithiobac. Weed Technol. 20:885-892.
- Bond, J.A. and Oliver, L.R. 2006. Comparative growth of Palmer amaranth (Amaranthus palmeri) accessions. Weed Sci. 54:121-126.
- Brewer, C.E., Oliver, L.R., and Scott, R.C. 2006. Update: Arkansas glyphosate-resistant common ragweed. Proc. South. Weed Sci. Soc. 59:188.
- Brewer, C.E., Oliver, L.R., Bararpour, M.T., and Lyons, F.H. 2006. Common ragweed interference in soybean. Abstr. Crop Prot. Assoc. 10:7-8.
- Griffith, G.M., Norsworthy, J.K., Scott, R.C., Smith, K.L., Oliver, L.R. and Bajwa, S.K. 2006. Palmer amaranth (Amaranthus palmeri) resistance to glyphosate in an Arkansas population. Abstr. Crop Prot. Assoc. 10:14-15.
- Stephenson, D.O., Oliver, L.R., and Gbur, E.E. 2006. Identification and characterization of pitted morningglory (Ipomoea lacunosa) ecotypes. Weed Sci. 54:78-86.
- Goldschmidt, N.V. and Oliver, L.R. 2006. Seedhead suppression of annual grasses with late-season herbicide applications. Proc. South. Weed Sci. Soc. 59:89.
- Goldschmidt, N.V. 2006. Weed seedbank reduction with late-season herbicide applications to annual grasses. M.S. Thesis. University of Arkansas, Fayetteville. 139 pp.
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Progress 01/01/05 to 12/31/05
Outputs
An extensive weed biology/ecology program is on-going in Arkansas to improve weed management practices and crop sustainability based on principles of crop-weed ecology. In crop production fields, a major seed load from weeds is deposited into the soil seedbank from weeds that escape early-season control. Two-year experiments were conducted in Arkansas to evaluate the effects of late-season applications of glyphosate, fluazifop, and clethodim on seed production potential of red rice and barnyardgrass, problem weeds in rice and soybean. One application of the labeled rate of glyphosate suppressed red rice seedheads 100% both years. Barnyardgrass seedhead suppression was 81% with two glyphosate applications the first year of the experiment; the second year, only one application reduced barnyardgrass seed production 100%. Two applications of fluazifop and clethodim were needed for adequate reduction of seed production. Late-season herbicide applications were an effective
and economical method for controlling grass escapes, providing late-season seedhead suppression, and reducing the soil seedbank. Limited research is available on the effects of weather on weed development, information that could aid in improving weed management practices. Development rate increased for velvetleaf and sicklepod as temperature, based on growing degree days (GDD), increased. However, development rate decreased for sicklepod, but increased for velvetleaf, as photoperiod increased. Photothermal base temperatures for plant development were determined for both species. Photothermal days for weeds can be used to determine weed development, which can be used to improve weed management models and management programs. Trials have been conducted to determine if residual herbicides should be used with glyphosate in a Roundup Ready soybean system. Early-season weed control was enhanced by using preemergence herbicides, although timely applications of glyphosate on small, actively
growing weeds provided adequate weed control and soybean yield. A new issue in Arkansas is the potential of glyphosate-resistant common ragweed to become a major weed problem. Studies have been initiated to evaluate the fitness and interference potential of the tolerant ragweed biotype as well as control programs for the weed. Increased reports of suspected ragweed tolerance indicate that weed control programs will have to be modified to control the resistant weeds and delay resistance development.
Impacts
Site-specific technology will play a key role in the future of pest management in order to increase crop production efficiency and sustainability. Characterizing variability within a weed species is a cornerstone of site-specific management. These studies help determine variability in populations of troublesome weeds so that optimum control measures can be implemented. Preventing seed rain by using herbicides at weed flowering may prevent ecological shifts to more troublesome species.
Publications
- Scott, R.C., Dillon, T.W., Meins, K.B., and Oliver, L.R. 2005. Investigation of a population of common ragweed suspected of glyphosate resistance. Proc. South. Weed Sci. Soc. 58:15.
- Scott, R.C., Burgos, N.L., and L.R. Oliver. 2005. ACCase-resistant ryegrass in Arkansas wheat. Proc. South. Weed Sci. Soc. 58:239.
- Alford, J.L. and Oliver, L.R. 2005. Determining weed development measuring growing degree days. Proc. South. Weed Sci. Soc. 58:221.
- Alford, J.L., Oliver, L.R., Brewer, C.E., and Bararpour, M.T. 2005. Effects of environmental conditions on Osprey (mesosulfuron) efficacy. Abstr. Ark. Crop Protection Assoc. 9:6-7.
- Bararpour, M.T., Bond, J.A., Brewer, C.E., and Oliver, L.R. 2005. Diclofop-resistant ryegrass control. Proc. South. Weed Sci. Soc. 58:30.
- Bararpour, M.T., Oliver, L.R., Burgos, N.R., and Scott, R.C. 2005. Ryegrass identification keys fact sheet. Ark. Coop. Extension Serv.: FSA2149-PD-11-05N. 2 pp.
- Bond, J.A., Stephenson, D.O., Barnes, J.W., Bararpour, M.T., and Oliver, L.R. 2005. Diclofop-resistant Italian ryegrass (Lolium multiflorum) control in imidazolinone-tolerant wheat. Weed Technol. 19:437-442.
- Brewer, C.E. and L.R. Oliver. 2005. Reducing seed rain with glyphosate applications. Proc. South. Weed Sci. Soc. 58:230.
- Brewer, C.E., Oliver, L.R., and Bararpour, M.T. 2005. Utility of residual herbicides in Roundup Ready soybean. Abstr. Ark. Crop Protection Assoc. 9:10-11.
- Goldschmidt, N.V., Oliver, L.R., Brewer, C.E., Bararpour, M.T., and Alford, J.L. 2005. Influence of seeding rate and glyphosate timing on weed management in soybean. Abstr. Ark. Crop Protection Assoc. 9:12-13.
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Progress 01/01/04 to 12/30/04
Outputs
An extensive weed biology/ecology program is on-going in Arkansas in order to improve weed management practices and crop sustainability based on principles of crop-weed ecology. Palmer amaranth accessions from humid areas in the United States produced more leaf area than plants from arid area and may be more competitive with crops. Genetic diversity could not be correlated to phenotypic diversity with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis; random amplified polymorphic DNA (RAPD); and intersimple sequence repeat (ISSR)-PCR. However, for pitted morningglory, 14 ISSR primers generated 1812 polymorphic fragments, which allowed separation of 64 United States accessions into four clusters: 1) Southeast Arkansas, Georgia, and Louisiana; 2) north Arkansas, Delaware, Kentucky, Missouri, and northeast North Carolina; 3) west-central Mississippi and one accession from west-central Arkansas; and 4) Alabama, Arkansas, east-cental
Mississippi, central North Carolina, and east-central Oklahoma. Variation was distributed along a latitudinal gradient but can be grouped geographically. Stage of growth of non-Roundup Ready grain sorghum cultivars determined severity of injury from glyphosate drift. The cultivars tolerated glyphosate rates of 0.001 to 0.01 lb ai/A, but 0.1 lb/A applied to 12-inch sorghum or at the early boot stage reduced yield because of severe injury and seedhead suppression. Three-leaf grain sorghum was more tolerant than larger plants to 0.1 lb/A glyphosate. Glyphosate was used to reduce biomass and seed production of spurred anoda (Anoda cristata), entireleaf morningglory (Ipomoea hederaceae var. integriuscula), hemp sesbania (Sesbania exaltata), and Florida pusley (Richardia scabra). Glyphosate at 1.5 lb/A applied at 3 weeks after emergence reduced biomass and seed production of all species. Glyphosate applied at weed flowering reduced seed production of all species 90 to 95%, but weed
flowering date was species specific. Reducing seed rain from weed species that have some tolerance to glyphosate is important to prevent ecological shifts to more troublesome weeds.
Impacts
Site-specific technology will play a key role in the future of pest management in order to increase crop production efficiency and sustainability. Characterizing variability within a weed species is a cornerstone of site-specific management. These studies help determine variability in populations of troublesome weeds so that optimum control measures can be implemented. Preventing seed rain by using herbicides at weed flowering may prevent ecological shifts to more troublesome species.
Publications
- Walker, E.R. and Oliver, L.R. 2004. Impact of late-season glyphosate applications on seed production of barnyardgrass (Echinochloa crus-galli), pitted morningglory (Ipomoea lacunosa), and sicklepod (Senna obtusifolia). Proc. South. Weed Sci. Soc. 57:216.
- Walker, E.R. and Oliver, L.R. 2004. Effect of glyphosate on barnyardgrass (Echinochloa crus-galli), pitted morningglory (Ipomoea lacunosa), and sicklepod (Senna obtusifolia) seed production. Abstr. Weed Sci. Soc. Am. 44:40-41.
- Alford, J.L., Oliver, L.R., Smith, K.L., and Bararpour, M.T. 2004. Differential tolerance of grain sorghum cultivars to glyphosate drift. Abstr. Ark. Crop Protection Assoc. 8:5.
- Bararpour, M.T., Oliver, L.R., and Burgos, N.R. 2004. Growth characteristics of Italian, rigid, poison, and perennial ryegrass. Proc. South. Weed Sci. Soc. 57:215.
- Bararpour, M.T., Oliver, L.R., and Burgos, N.R. 2004. Vegetative and reproductive characteristics of Italian, rigid, poison, and perennial ryegrass. Abstr. Ark. Crop Protection Assoc. 8:3.
- Bond, J.A. and Oliver, L.R. 2004. Variation among Palmer amaranth (Amaranthus palmeri) accessions. Proc. South. Weed Sci. Soc. 57:212.
- Bond, J.A. and Oliver, L.R. 2004. Comparative growth and response to herbicides of Palmer amaranth (Amaranthus palmeri) accessions. Abstr. Weed Sci. Soc. Am. 44:88.
- Bond, J.A. 2004. Variation in Palmer amaranth (Amaranthus palmeri) across the southern United States. Ph.D. dissertation. University of Arkansas. Fayetteville, AR. 99 pp.
- Goldschmidt, N.V. and Oliver, L.R. 2004. Late-season herbicide applications to reduce the annual grass seed bank. Abstr. Ark. Crop Protection Assoc. 8:2-3.
- Stephenson, D.O. 2004. Identification and characterization of pitted morningglory (Ipomoea lacunosa) ecotypes and biotypes. Ph.D. dissertation. University of Arkansas. Fayetteville, AR. 181 pp.
- Stephenson, D.O. and Oliver, L.R. 2004. Genetic variation of pitted morningglory (Ipomoea lacunosa) accessions using inter-single sequence repeats. Abstr. Weed Sci. Soc. Am. 44:66.
- Walker, E.R. 2004. Late-season glyphosate applications in glyphosate-tolerant soybean to reduce soil seedbank. Ph.D. dissertation. University of Arkansas. Fayetteville, AR. 258 pp.
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Progress 01/01/03 to 12/31/03
Outputs
Studies of weed biology/ecology are on-going in Arkansas so that weed management practices can be improved based on crop-weed ecology. Palmer amaranth accessions in the western and eastern portions of the species range grew differently based on differences in leaf area ratio, specific leaf area, net assimilation rate, and stem-leaf ratio among accessions. Therefore, Palmer amaranth accessions do respond to the climatic conditions of their area of origin. Arkansas accessions displayed variable characteristics, often showing characteristics either intermediate between those for western and eastern accessions or similar to western or eastern accessions. Inconsistent growth characteristics for Arkansas accessions suggest greater diversity of Palmer amaranth within Arkansas compared with other areas. Palmer amaranth plants originating in humid areas produce more leaf area than plants from more arid climates and should be more competitive with crops. Therefore, producers in
states located in the southern and eastern United states should be extremely sensitive to changes in weed growth when planning control strategies for fields where Palmer amaranth infestations are severe. A study was conducted to determine the possible genetic variability among pitted morningglory accessions collected from across their indigenous range using inter-simple sequence repeats (ISSR). Fourteen of the fifteen ISSR primers amplified different fragments of DNA that are polymorphic, indicating genetic variability among pitted morningglory accessions. An average of 134 fragments per primer were scored. Cluster analysis grouped DNA fragments into four clusters. In support of these findings other research has shown the existence of morphological variation within these same pitted morningglory samples. A field experiment was conducted to determine morphological differences among Lolium species and Arkansas diclofop-resistant ryegrass populations. All of the resistant ryegrass
populations from Arkansas were identified as Italian ryegrass, which had erect to prostrate growth habit, greenish to reddish color, green to red nodes, glumes shorter than spikelets (10 to 14 mm), and medium-sized seeds with 1- to 3-mm awns. Therefore, morphological variability exists in Arkansas diclofop-resistant Italian ryegrass.
Impacts
Site-specific technology will play a key role in the future of pest management in order to increase crop production efficiency and sustainability. Characterizing variability within a weed species is a cornerstone of site-specific management. These studies help determine variability in populations of troublesome weeds so that optimum control measures can be implemented.
Publications
- Popp, M.P., Manning, P.M., Keisling, T.C., Gordon, E.C., and Oliver, L.R. 2002. Analysis of a novel bedded planting system for dry clay soil management of full-season and double-crop soybean. Communications Soil Sci. and Plant Analysis. 34:2925-2950.
- Stephenson, D.O. and Oliver, L.R. 2003. Morphological identification and characterization of accessions within the pitted morningglory (Ipomoea lacunosa) species. Abstr. Weed Sci. Soc. Am. 43:511.
- Walker, E.R. and Oliver, L.R. 2003. Influence of glyphosate on seed production of barnyardgrass (Echinochloa crus-galli), pitted morningglory (Ipomoea lacunosa), and sicklepod (Senna obtusifolia). Abstr. Ark. Crop Prot. Assoc. 7:10-11.
- Bararpour, M.T., Oliver, L.R., and Burgos, N.R. 2003. Morphological characteristics of the Arkansas diclofop-resistant ryegrass population. Proc. South. Weed Sci. Soc. 56:187.
- Barnes, J.W. and Oliver, L.R. 2003. Cultural practices and glyphosate applications for sicklepod control in soybean. Weed Technol. 17:429-440.
- Brewer, C.E. and Oliver, L.R. 2003. Utilizing late-season glyphosate applications to reduce weed seed rain. Abstr. Ark. Crop Prot. Assoc. 7:17. Edwards, J.T. and Oliver, L.R. 2003. Emergence and growth of trumpetcreeper (Campsis radicans) as affected by rootstock size. Weed Technol. (accepted)
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Progress 01/01/02 to 12/31/02
Outputs
Studies of weed biology/ecology are on-going in Arkansas so that weed management practices can be improved based on crop-weed ecology. Experiments are being conducted to investigate the possible existence of pitted morningglory (Ipomoea lacunosa) biotypes based on their morphology and susceptibility to glyphosate. Accessions were collected from areas of the U.S. where pitted morningglory grows indigenously. There were no differences in glyphosate susceptibility among accessions from Arkansas, the central area of pitted morningglory native range, but other accessions differed in susceptibility even though environmental conditions and plant size were similar at glyphosate application. Because of the differing susceptibilities and morphological and physiological characteristics, the existence of pitted morningglory ecotypes is probable. Palmer amaranth (Amaranthus palmeri) accessions are also being studied. Variations in growth and development were noted among geographic
regions. Based on growth analysis for different accessions, producers in northern Arkansas should initiate Palmer amaranth control measures prior to 4 weeks after emergence. These studies will aid in determining optimal application timing for control of weeds depending on ecotypical growth parameters. A triple-crop rotation of short-season corn, early-maturing, soybean, and winter wheat increases the need for maximum weed control with minimum herbicide carryover but can be used to better utilize rainfall and diversify a producer's income. Mixed drilling or broadcasting of Roundup Ready and conventional soybean cultivars continues to show promise, especially at 100,000 to 200,000 seed/A of an upright Roundup Ready cultivar with 200,000 seed/A of a conventional cultivar. This system uses intraspecific competitiveness of soybean to suppress early-season weeds and reduce the number of glyphosate applications needed during the season. Studies are being conducted to identify optimum
glyphosate rates and timings to reduce weed seed production, germination, and viability in a glyphosate-tolerant soybean production system, ultimately reducing the soil seedbank. Sequential glyphosate applications at 0.5 lb/A applied to late-season weed escapes at initial weed flowering in glyphosate-tolerant soybean are effective at reducing weed pressure of certain weed species, such as barnyardgrass and pitted morningglory, the following year, with no associated reduction in soybean yield.
Impacts
Understanding weed emergence and flowering patterns, seed production potential, seed longevity, and soil seedbank dynamics allows production practices to be altered to improve the competitive advantage of soybeans, which can reduce herbicide inputs and increase yields for soybean producers. These studies also aid in predicting the dominance of species in various production practices and how control methods may affect seed production, emergence, and dynamics of the soil seedbank, which increases success of future crop production.
Publications
- Bararpour, M.T., Oliver, L.R., and Burgos, N.R. 2002. Vegetative and reproductive characteristics of Arkansas resistant ryegrass. Abstr. Ark. Crop Prot. Assoc. 6:12-13.
- Bond, J.A. and Oliver, L.R. 2002. Comparative growth of Arkansas Palmer amaranth (Amaranthus palmeri) accessions. Abstr. Ark. Crop Prot. Assoc. 6:10-11.
- Norsworthy, J.K. and Oliver, L.R. 2002. Pitted morningglory interference in drill-seeded glyphosate-tolerant soybean. Weed Sci. 50:26-33.
- Norsworthy, J.K. and Oliver, L.R. 2002. Hemp sesbania interference in drill-seeded glyphosate-tolerant soybean. Weed Sci. 50:34-41.
- Norsworthy, J.K. and Oliver, L.R. 2002. Effect of irrigation, soybean (Glycine max) density, and glyphosate on hemp sesbania (Sesbania exaltata) and pitted morningglory (Ipomoea lacunosa) interference in soybean. Weed Technol. 16:7-17.
- Oliver, L.R. and Barnes, J.W. 2002. Influence of weed density, emergence date, herbicide application, and tillage level on sicklepod (Senna obtusifolia) seed bank dynamics. Proc. South. Weed. Sci. Soc. 55:112-113.
- Oliver, D., Barrentine, J., and McClelland, M. 2002. Specific weed control for 2001. Crop, Soil, and Environmental Sciences Department, 297 pp.
- Popp, M.P., Keisling, T.C., McNew, R., Oliver, L.R., Dillon, C.R., and Wallace, D.M. 2002. Planting date, cultivar, and tillage system effects on dryland soybean production. Agron. J. 94:81-88.
- Stephenson, D.O., IV., Oliver, L.R., Barnes, J.W., Bond, J.A., and Walker, E.R. 2002. Use of glyphosate-susceptibility to identify pitted morningglory (Ipomoea lacunosa) ecotypes. Proc. South. Weed Sci. Soc. 55:183.
- Walker, E.R. and Oliver, L.R. 2002. Soil seedbank reduction in glyphosate-tolerant soybean. Proc. South. Weed Sci. Soc. 55:206-207.
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