Progress 07/01/98 to 06/30/04
Outputs
A seven-year experiment with glyphosate-resistant soybean was initiated in 1998 at the Black Belt Branch Experiment Station near Brooksville, MS. The experiment was designed to observe weed population shifts in a variety of different continuous conventional and glyphosate weed management systems. The field size was 7.8 ha, and prior to 1998 was in tall fescue (Festuca arundanacea Schreb.) pasture. Each year a 10-m by 10-m grid was imposed on the field using a global positioning system. At each grid location, a 1-m2 quadrate was used to determine the weed species present. In 1998 the most prevalent weed was yellow foxtail (Setaria glauca L.); however, in 2003 and 2004, four of the most prevalent weed species were yellow nutsedge (Cyperus esculentus L.), horsenettle (Solanum carolinense L.), broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash], and hophornbeam copperleaf (Acalypha ostryifolia Riddell). Field experiments were conducted to evaluate the effects of
residual grass herbicides applied mid-POST in tank-mixes with glyphosate on early-planted glyphosate-resistant soybean at two row spacings. Glyphosate was also applied alone at early or mid-POST, as well as sequential applications at these timings. It was thought that tank mixtures of glyphosate with metolachlor, flufenacet, dimethenamid, or pendimethalin might provide added residual control for subsequent weed flushes that would arise after the initial control from glyphosate. Interest in narrow row crop production has existed since 1939. Narrow row crop production offers yield advantages due to more efficient use of sunlight and quicker canopy closure. This study was conducted to determine the impact of various row spacings on soybean yield and weed management programs. Seeding rates used in this study were: 123500, 247100, 371000, and 494200 seeds per hectare. For each seeding rate, herbicide programs were determined in the following manner: total glyphosate program using the
herbicide recommendation software HADSS (RR HADSS), total glyphosate program standard for our geographical area (RR conventional), conventional herbicide program using HADSS (conventional HADSS), and conventional program standard for our geographical area (conventional standard). Over 85% control of hemp sesbania and johnsongrass was obtained with all weed control programs regardless of seeding rate. Pitted morningglory control was also more than 80% for all programs with the exception of the conventional standard program. Control of pitted morningglory control was variable (71 - 85%), depending on seeding rate. At least 90% sicklepod control was observed with each total glyphosate program; however, control was less than 60% with both conventional programs. The highest yields were obtained using a total glyphosate program at seeding rates of 247100, 371000, and 494200 seeds per hectare. Based on weed control and yield results, the RR conventional weed control program at a seeding rate
of 247100 seeds per hectare would be the optimum system for soybean production using 48 cm rows.
Impacts
Shifts in weed populations occur when any single herbicide system is used over an extended period of time, whether conventional or glyphosate systems. Judicious use of a variety of herbicide programs will help insure the viability of these programs, and prevent the selection of more tolerant or resistant weeds. In narrow row glyphosate-resistant soybean production systems, seeding rate plays an important role in effective weed control. Reducing seeding rate below recommended levels increased weed control costs, while higher seeding rates resulted in more seed costs with no benefits in weed control. Tank mixtures of residual herbicides with glyphosate extended the period of weed control such that a second glyphosate application was often not necessary.
Publications
- Shaw, D. R., W. H. Morris, E. P. Webster, and D. B. Smith. 2000. Spray volume and droplet size effects on herbicide deposition and common cocklebur (Xanthium strumarium) control. Weed Technol. 14:321-328.
- Smith, D. B., S. D. Askew, W. H. Morris, D. R. Shaw, and M. Boyette. 2000. Droplet size and leaf morphology effects on pesticide spray deposition. Trans. Am. Soc. Agric. Eng. 43:255-259.
- Akin, D. S., and D. R. Shaw. 2001. Purple nutsedge (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus) control in glyphosate-tolerant soybean (Glycine max). Weed Technol. 15:564-570.
- Akin, D. S., and D. R. Shaw. 2004. In-season applications of glyphosate to control redvine (Brunnichia ovata) in glyphosate-tolerant soybean. Weed Technology 17:241-248.
- Askew, S. D., D. R. Shaw, and J. E. Street. 2000. Graminicide application timing influences red rice (Oryza sativa) control and seedhead suppression in soybean (Glycine max). Weed Technol. 14:116-121.
- Bennett, A. C., and D. R. Shaw. 2000. Effect of Glycine max cultivar and weed control on weed seed characteristics. Weed Sci. 48:431-435.
- Bennett, A. C., and D. R. Shaw. 2000. Effect of preharvest desiccants on Group IV Glycine max seed viability. Weed Sci. 48:426-430.
- Bennett, A. C., and D. R. Shaw. 2000. Effect of preharvest desiccants on weed seed production and viability. Weed Technol. 14:530-537.
- Buehring, N. W., G. R. W. Nice, and D. R. Shaw. 2003. Sicklepod (Senna obtusifolia) control and soybean (Glycine max) response to soybean row spacing and population in three weed management systems. Weed Technol. 16:131-141.
- Medlin, C. R., and D. R. Shaw. 2000. Economic comparison of broadcast and site-specific herbicide applications in nontransgenic and glyphosate-tolerant soybean (Glycine max). Weed Sci. 48:653-670.
- Nice, G. R. W., N. W. Buehring, and D. R. Shaw. 2001. Sicklepod (Senna obtusifolia) response to shading, soybean (Glycine max) row spacing, and population in three management systems. Weed Technol. 15:155-162.
- Norris, J. L., D. R. Shaw, and C. E. Snipes. 2001. Weed control from herbicide combinations with three formulations of glyphosate. Weed Technol. 15:552-558.
- Norris, J. L., D. R. Shaw, and C. E. Snipes. 2002. Influence of row spacing and residual herbicides on weed control in glufosinate-resistant soybean (Glycine max). Weed Technol. 16:319-325.
- Palmer, E. W., D. R. Shaw, and J. C. Holloway. 2000. Broadleaf weed control in soybean (Glycine max) with CGA-277476 and four postemergence herbicides. Weed Technol. 14:617-623.
- Shaw, D. R., and J. C. Arnold. 2002. Weed control from herbicide combinations with glyphosate. Weed Technol. 16:1-6.
- Shaw, D. R., J. C. Arnold, C. E. Snipes, D. H. Laughlin, and J. A. Mills. 2001. Comparison of glypyhosate-resistant and conventional soybean (Glycine max) herbicide systems. Weed Technol. 15:676-685.
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Progress 01/01/03 to 12/31/03
Outputs
It has been theorized that complete reliance on glyphosate for weed control, particularly in continuous cropping or in rotations of glyphosate-resistant crops, will result in a shift in the weed spectrum towards more tolerant weed species, similar to what occurred with the ALS inhibiting herbicides in the late 1980s and early 1990s. Previous research has also shown that more diverse populations of perennial weeds with greater densities developed in reduced tillage systems. However, these populations and densities may be highly dependent on management practices. Little research has been found that deals with the long-term effects of weed management using glyphosate-resistant soybean on weed populations in a no-till production system. Research was conducted at the Black Belt Branch Experiment Station near Brooksville, MS from 1998 to present in a no-till production system. Weed control strategies evaluated were various combinations of glyphosate and conventional
herbicide systems. Large (0.3 ha) plots were used to better delineate weed population changes over time. The highest level of weed control was obtained with multiple applications of glyphosate POST, regardless of burndown treatment. Plots that received only conventional herbicides had higher populations of perennial species such as horsenettle (Solanum carolinense L.), broomsedge (Andropogon virginicus L.), and perennial tree species [e.g. hackberry (Celtis spp.)]. Decreased weed control following conventional herbicides may be, in part, due to delayed herbicide application due to environmental conditions. However, high levels of weed control following glyphosate demonstrated flexibility in timing of herbicide application using glyphosate. Increases in pitted morningglory were noted following continuous glyphosate usage, indicating selection toward species more tolerant to glyphosate.
Impacts
Shifts in weed populations occur when any single herbicide system is used over an extended period of time, whether conventional or glyphosate systems. Judicious use of a variety of herbicide programs will help insure the viability of these programs, and prevent the selection of more tolerant or resistant weeds.
Publications
- Shaw, D. R., and C. S. Bray. 2003. Foreign material and seed moisture in glyphosate-resistant and conventional soybean systems. Weed Technology 17:389-393.
- Easley, J. W., D. R. Shaw, and C. J. Gray. 2003. Tank mixtures for potential improvement of Roundup Ready soybean weed control. Proc. South. Weed Sci. 56:69.
- Gray, C. J., D. R. Shaw, F. E. LaMastus, and J. W. Easley. 2003. Weed shifts following pasture conversion with five years of soybean production. Proc. South. Weed Sci. 56:178.
- Smith, M. C., D. R. Shaw, and F. S. Kelley. 2003. A comparison of weed control with commercially available glyphosate formulations. Proc. South. Weed Sci. 56:38.
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Progress 01/01/02 to 12/31/02
Outputs
Research was conducted to compare weed scouting methods for site-specific weed management. The first employed overlaying fields with 025-ha grids, then physically counting weeds at the sampling points. The second involved tracing the perimeters of weed patches with a GPS unit based on visual estimates of above-threshold populations. In addition, 0.5-m multispectral imagery was collected and analyzed. Perimeter tracing showed general weed distributions and patches of high weed density; however some were missed. Weedy and weed-free areas were effectively differentiated from imagery. Perimeter tracing and imagery both show promise for site-specific weed management, but physically counting weeds is too time-consuming to be practical. A 5-year experiment designed to observe weed population shifts in a continuous monoculture was completed. The six most prevalent weed species were yellow nutsedge, horsenettle, large crabgrass, broadleaf signalgrass, smallflower morningglory,
and hophornbeam copperleaf. The greatest temporal stability came with hophornbeam copperleaf and yellow nutsedge. These species were predominately located in the higher and lower elevations of the field, respectively. Overall, the temporal stability of the field tended to be variable and unstable due to varying environmental conditions, as well as changes in herbicide programs. Weed populations were also monitored on two fields to determine the ability of remote sensing to detect these populations. Hyperspectral reflectance was measured for four weed species: sicklepod, pitted morningglory, entireleaf morningglory, and horsenettle, as well as bare soil. Data were analyzed using linear discriminant analysis (LDA) with indices as classification discriminants. Data were also analyzed using customized software, which performed a feature extraction technique that classified weed species and bare soil using spectral bands chosen as best for discriminating species. Classification accuracies
ranged from 29 to 99% for LDA. As expected, classification accuracies for entireleaf morningglory and pitted morningglory were low, since these are two closely-related species. Classification accuracies were slightly better using spectral bands, and ranged from 44 to 97%. Field studies were conducted to compare weed control with commercial glyphosate formulations. Weed control differentiation based on glyphosate formulation was minimal. Research also compared glyphosate alone and with various tank mixtures of other herbicides. Tank mixtures improved control of several species. Pitted morningglory and hemp sesbania control were both increased with the addition of diclosulam and fomesafen to glyphosate. The best prickly sida and velvetleaf control occurred when glyphosate was tank-mixed with diclosulam. Effective barnyardgrass control was achieved with all treatments; however, slight antagonism occurred when glyphosate was tank-mixed with fomesafen.
Impacts
Site-specific weed management can potentially reduce herbicide applications, providing both economic and environmental benefits. Remote sensing technology is maturing to the point that its applications in precision agriculture, and specifically in site-specific weed management, are evident. Transgenic soybean with glyphosate resistance provides effective, economical, and broad-spectrum weed control with glyphosate alone or with other herbicides.
Publications
- Kelley, F. S., D. R. Shaw, T. H. Koger, and F. E. LaMastus. 2002. Determining the optimal sampling density for scouting and mapping weed populations. Proc. South. Weed Sci. Soc. 55:190.
- Koger, T. H., D. R. Shaw, C. J. Gray, and K. N. Reddy. 2002. Potential use of remote sensing for detection of late-season weed infestations. Weed Sci. Soc. Am. Abstr. 42:3.
- Norris, J. L., D. R. Shaw, and C. E. Snipes. 2002. Influence of row spacing and residual herbicides on weed control in glufosinate-resistant soybean (Glycine max). Weed Technol. 16:319-325.
- Shaw, D. R., and J. C. Arnold. 2002. Weed control from herbicide combinations with glyphosate. Weed Technol. 16:1-6.
- Gray, C. J., D. R. Shaw, W. B. Henry, and M. L. Mortimer. 2002. Potential for crop and weed species differentiation using hyperspectral reflectance. Weed Sci. Soc. Am. Abstr. 42:76.
- Gray, C. J., D. R. Shaw, and M. L. Tagert. 2002. Control of volunteer Roundup Ready crops in soybean and cotton systems. Proc. South. Weed Sci. Soc. 55:40.
- Griffin, R. M., D. H. Poston, D. R. Shaw, and F. S. Kelley. 2002. Weed control in maturity group IV soybean grown in MS at various row spacings and planting dates. Proc. South. Weed Sci. Soc. 55:150.
- Kelley, F. S., D. R. Shaw, and R. M. Griffin. 2002. Preplant burndown and nutsedge control in soybean. Proc. South. Weed Sci. Soc. 55:42.
- Koger, T. H., D. R. Shaw, W. B. Henry, F. S. Kelley, L. M. Bruce, and K.N. Reddy. 2002. Isolation of distinguishable classification features for pitted morningglory (Ipomoea lacunosa) from hyperspectral remote sensing data. Proc. South. Weed Sci. Soc. 55:181.
- Koger, T. H., D. R. Shaw, F. S. Kelley, L. M. Bruce, and K.N. Reddy. 2002. Detection of pitted morningglory (Ipomoea lacunosa) in soybean with supervised data analysis techniques. Proc. South. Weed Sci. Soc. 55:129.
- Henry, W. B., D. R. Shaw, K. R. Reddy, L. M. Bruce, H. D. Tamhankar, and T. H. Koger. 2002. Detection of moisture stress using hyperspectral reflectance data from common cocklebur, sicklepod, and soybean. Proc. South. Weed Sci. Soc. 55:123.
- Henry. W. B., D. R. Shaw, K. R. Reddy, L. M. Bruce, and M. C. Smith. 2002. Detection of herbicide injury using hyperspectral reflectance data from corn, soybean, and four weed species. Weed Sci. Soc. Am. Abstr. 42:28.
- Tagert, M. L., D. R. Shaw, C. Smith, and T. H. Koger. 2002. Greenhouse and field evaluations of glyphosate formulations. Weed Sci. Soc. Am. Abstr. 42:43.
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Progress 01/01/01 to 12/31/01
Outputs
This research was conducted to determine if remote sensing could be used to detect the presence, and perhaps the degree, of moisture stress in common cocklebur (Xanthium strumarium L.), sicklepod [Senna obtusifolia (L.) Irwin and Barnaby], and soybean [Glycine max (L.) Merr.]. Another goal of this research was to determine if moisture stress impacts the ability to correctly differentiate species. Data suggest that, within a species, plants grown at 100% and 40% moisture could be correctly classified approximately 60 to 80% of the time, depending upon species and statistical analyses. Three ranges of leaf water potential were created, and common cocklebur was correctly classified into these ranges 58 to 68% of the time. Although moisture stress did influence the spectral response of these species, it did not decrease the ability to correctly classify between species. The trend was that as moisture stress increased, so too did the ability to distinguish between species.
Research was conducted on two fields in Brooksville, MS to evaluate the optimal sampling density required to accurately scout and map weed populations. In 2001, 50-m grids were imposed on two soybean fields, East field (15 ha) and South field (16 ha). Weed species were counted using a 4-m2 sample size at each grid point. Using the data collected on a 10-m grid system, the variance was analyzed between the two sample sizes. The five most prevalent weeds in these two fields were used in this analysis. East field detection capabilities with 50 and 10-m grid sizes indicate sicklepod, pitted morningglory, and purple nutsedge were not significantly different with respect to grid sizes. The use of 50-m grids tended to overestimate entireleaf morningglory populations and underestimate horsenettle populations. South field detection capabilities with 50 and 10-m grid sizes also differed with respect to weed species. Entireleaf morningglory populations were overestimated with the 50-m grid. In
addition, entireleaf morningglory was the only weed species that differed with the two grid sizes at both locations. Based on this research, the weed spectrum within a field would dictate the sample grid size. A field experiment was conducted near Starkville, MS to evaluate the control of both volunteer glyphosate-resistant soybean and cotton in desired glyphosate-resistant soybean and cotton systems. Cultivation incorporated into a producer's herbicide program increased control of volunteer glyphosate-resistant crops. Herbicide applications alone may not control volunteer crops adequately, particularly if no desirable crop to volunteer crop height differential is established. This may result in volunteer glyphosate-resistant crops being particularly problematic in no-till production systems.
Impacts
Remote sensing and site-specific weed management can substantially reduce the amount of herbicides applied, thus providing economical and environmental benefits. Sampling of weed populations without remote sensing is difficult and costly, given the variability in weed populations across fields. Transgenic herbicide systems provide substantial improvements in weed control over conventional systems, but transgenic, herbicide-resistant varieties can pose problems as weeds in subsequent crops.
Publications
- Baughman, T. A., D. R. Shaw, E. P. Webster, and M. Boyette. 2001. Effect of cotton (Gossypium hirsutum) tillage systems on off-site movement of fluometuron, norflurazon, and sediment in runoff. Weed Technol. 15:184-189.
- Medlin, C. R., D. R. Shaw, M. S. Cox, P. D. Gerard, M. J. Abshire, and M. C. Wardlaw. 2001. Using soil parameters to predict weed infestations in soybean (Glycine max). Weed Sci. 49:367-374.
- Nice, G. R. W., N. W. Buehring, and D. R. Shaw. 2001. Sicklepod (Senna obtusifolia) response to shading, soybean (Glycine max) row spacing, and population in three management systems. Weed Technol. 15:155-162.
- Norris, J. L., D. R. Shaw, and C. E. Snipes. 2001. Weed control from herbicide combinations with three formulations of glyphosate. Weed Technol. 15:552-558.
- Rankins, A., Jr., D. R. Shaw, and M. Boyette. 2001. Perennial grass filter strips for reducing herbicide losses in runoff. Weed Sci. 49:647-651.
- Seifert, S., D. R. Shaw, W. L. Kingery, C. E. Snipes, and R. A. Wesley. 2001. Imazaquin mobility and persistence in a Sharkey clay soil as influenced by tillage systems. Weed Sci. 49:571-577.
- Seifert, S., D. R. Shaw, R. M. Zablotowicz, R. A. Wesley, and W. L. Kingery. 2001. Effect of tillage on microbial characteristics and herbicide dissipation in a Sharkey clay soil. Weed Sci. 49:685-693.
- Shankle, M. W., D. R. Shaw, and M. Boyette. 2001. Confirmation of an enzyme-linked immunosorbent assay to detect fluometuron in soil. Weed Technol. 15:669-675.
- Shaw, D. R., J. C. Arnold, C. E. Snipes, D. H. Laughlin, and J. A. Mills. 2001. Comparison of glypyhosate-resistant and conventional soybean (Glycine max) herbicide systems. Weed Technol. 15:676-685.
- Akin, D. S., and D. R. Shaw. 2001. Purple nutsedge (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus) control in glyphosate-tolerant soybean (Glycine max). Weed Technol. 15:564-570.
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Progress 01/01/00 to 12/31/00
Outputs
Soybean production systems with glyphosate in transgenic cultivars provided better economic returns than conventional herbicide systems in the same cultivars. Soil-applied herbicides such as flumetsulam, imazaquin, chlorimuron plus metribuzin, and sulfentrazone plus chlorimuron enhanced control of some weeds over glyphosate alone. Tank-mixing glyphosate with acifluorfen, fomesafen, chlorimuron, cloransulam, and cloransulam plus flumetsulam at reduced rates was also beneficial in improving control of these weeds, and in some instances provided optimum weed control with fewer herbicide applications. Reducing soybean row spacing did not improve weed control in soybean as much in 2000 as in 1999, primarily due to drought conditions which did not lead to canopy closure in either wide or narrow row spacings. Aerial multispectral images were used in an attempt to determine reflectance differences between pitted morningglory, entireleaf morningglory, common cocklebur, and
sicklepod. Discriminant analysis indicated a high degree of correct classification for pitted morningglory and entireleaf morningglory, with greater error associated with common cocklebur and sicklepod classifications. Images collected later in the season increased the classification accuracy, primarily due to weeds being larger and pixels being more completely filled with uniform weed cover. Wavelet analysis provided a means of discriminating between weeds, soybean, soil, and cover crop residue accurately. This technique also was useful in detecting soybean and cotton stress caused by purple nutsedge or yellow nutsedge via leaf reflectance.
Impacts
Transgenic herbicide-tolerant systems effectively and economically control a broad spectrum of troublesome weeds in Mississippi. This research is helping to choose from the myriad of herbicide options available to producers, highlighting strengths and weaknesses. Remote sensing can play a significant role in detecting weed presence in specific portions of fields. This will enable site-specific applications of herbicides, providing both economic and environmental benefits.
Publications
- Shaw, D. R., W. H. Morris, E. P. Webster, and D. B. Smith. 2000. Spray volume and droplet size effects on herbicide deposition and common cocklebur (Xanthium strumarium) control. Weed Technol. 14:321-328.
- Smith, D. B., S. D. Askew, W. H. Morris, D. R. Shaw, and M. Boyette. 2000. Droplet size and leaf morphology effects on pesticide spray deposition. Trans. Am. Soc. Agric. Eng. 43:255-259.
- Webster, E. P., D. R. Shaw, T. A. Baughman, C. E. Snipes, and C. T. Bryson. 2000. Influence of cultivation timing on pyrithiobac performance in cotton (Gossypium hirsutum). Weed Technol. 14:116-121.
- Askew, S. D., D. R. Shaw, and J. E. Street. 2000. Graminicide application timing influences red rice (Oryza sativa) control and seedhead suppression in soybean (Glycine max). Weed Technol. 14:116-121.
- Bennett, A. C., and D. R. Shaw. 2000. Effect of Glycine max cultivar and weed control on weed seed characteristics. Weed Sci. 48:431-435. Bennett, A. C., and D. R. Shaw. 2000. Effect of preharvest desiccants on Group IV Glycine max seed viability. Weed Sci. 48:426-430.
- Bennett, A. C., and D. R. Shaw. 2000. Effect of preharvest desiccants on weed seed production and viability. Weed Technol. 14:530-537.
- Medlin, C. R., and D. R. Shaw. 2000. Economic comparison of broadcast and site-specific herbicide applications in nontransgenic and glyphosate-tolerant soybean (Glycine max). Weed Sci. 48:653-670.
- Medlin, C. R., D. R. Shaw, P. D. Gerard, and F. E. LaMastus. 2000. Using remote sensing to detect weed infestations in soybean (Glycine max). Weed Sci. 48:393-398.
- Palmer, E. W., D. R. Shaw, and J. C. Holloway. 2000. Broadleaf weed control in soybean (Glycine max) with CGA-277476 and four postemergence herbicides. Weed Technol. 14:617-623.
- Shaw, D.R., and C.L. Hill. 2000. Precision agriculture and remote sensing. Space 2000, Am. Civil Eng. Soc. 32:455-460.
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Progress 01/01/99 to 12/31/99
Outputs
Soybean production systems using transgenic, glyphosate-tolerant cultivars provided better economic returns than conventional herbicide systems, except when lower-yielding cultivars were selected or when weeds such as hemp sesbania were marginally controlled. Glufosinate was highly effective on a wide range of grass and broadleaf weeds in transgenic, glufosinate-tolerant cultivars. Soil-applied herbicides such as flumetsulam, imazaquin, chlorimuron plus metribuzin, and sulfentrazone plus chlorimuron enhanced control of pitted morningglory and hemp sesbania over glyphosate alone. Tank-mixing glyphosate with acifluorfen, fomesafen, chlorimuron, cloransulam, and cloransulam plus flumetsulam at reduced rates was also beneficial in improving control of these weeds, and in some instances provided optimum weed control with fewer herbicide applications. Reducing soybean row spacing improved soybean competitiveness, which reduced the need for a second postemergence application
of glufosinate or glyphosate, as was true when soybean seeding rates were increased. Glyphosate was most effective in reducing populations of the perennial weeds redvine and yellow nutsedge when three applications were used, or when two applications were used at higher rates or separated by more time between applications. Aerial multispectral images were used in an attempt to determine reflectance differences between pitted morningglory, entireleaf morningglory, common cocklebur, and sicklepod. Discriminant analysis indicated a high degree of correct classification for pitted morningglory and entireleaf morningglory, with greater error associated with common cocklebur and sicklepod classifications. Images collected later in the season increased the classification accuracy, primarily due to weeds being larger and pixels being more completely filled with uniform weed cover.
Impacts
Transgenic herbicide-tolerant systems effectively control weeds, but conventional systems will play a role. This research is helping to choose from the myriad of options available to producers, highlighting strengths and weaknesses. Remote sensing can play a significant role in detecting weed-infested areas of fields. This will be a major advancement in enabling site-specific weed management.
Publications
- Akin, D. S., Shaw, D. R., and Nice, G. W. 1999. Effects of Roundup Ultra and conventional herbicides on yellow nutsedge (Cyperus esculentus) in soybean. Proc. South. Weed Sci. Soc. 52:248.
- Akin, D. S., Shaw, D. R., and Norris, J. L. 1999. Efficacy of ALS-inhibiting broadleaf herbicides tank-mixed with Roundup Ultra in Roundup Ready soybean. Proc. South. Weed Sci. Soc. 52:54.
- Arnold, J. C., Shaw, D. R., and Norris, J. L. 1999. Assessment of efficacy and economics in Roundup Ready versus conventional soybean programs. Proc. South. Weed Sci. Soc. 52:217.
- Bennett, A. C., Shaw, D. R., and Akin, D. S. 1999. Efficacy of diphenylether herbicides tank-mixed with glyphosate. Proc. South. Weed Sci. Soc. 52:59.
- Bennett, A. C., Shaw, D. R., and Rankins, A., Jr. 1999. Effect of conventional herbicides on glyphosate-tolerant soybean injury and yield. Weed Sci. Soc. Am. Abst. 39:138.
- Brommer, C. L., and Shaw, D. R. 1999. Effect of broadleaf herbicides and adjuvants on the uptake and translocation of glyphosate in morningglory. Proc. South. Weed Sci. Soc. 52:245.
- Brommer, C. L., Shaw, D. R., Reddy, K. N., and Duke, S. O. 1999. Interaction of BAS 625 with selected broadleaf tank mixtures. Weed Sci. Soc. Am. Abst. 39:243.
- Flint, S. G., Holloway, J. C., Shaw, D. R., and Smith, M. C. 1999. Soil applied herbicide programs in a Roundup Ready system. Proc. South. Weed Sci. Soc. 52:58.
- Medlin, C. R., Shaw, D. R., Cox, M. S., Gerard, P. D., and LaMastus, F. E. 1999. Weed dispersal and soil relationships described by statistical analysis techniques. Proc. South. Weed Sci. Soc. 52:166.
- Nice, G. W., Buehring, N. W., Shaw, D. R., Dobbs, R., Jones, G., and Rankins, A., Jr. 1999. Effects of soybean row spacing, population density, and herbicide management techniques on sicklepod (Senna obtusifolia) and soybean production. Proc. South. Weed Sci. Soc. 52:248.
- Norris, J. L, Shaw, D. R., Snipes, C. E., and Akin, D. S. 1999. Influence of row spacing and residual herbicides on weed control in Roundup Ready and Liberty Link soybean. Proc. South. Weed Sci. Soc. 52:53.
- Palmer, E. W., Shaw, D. R., and Holloway, J. C., Jr. 1999. Evaluation of soil-applied herbicides in sequential programs with CGA-277476 in soybean (Glycine max). Weed Technol. 13:271-275.
- Palmer, E. W., Shaw, D. R., and Holloway, J. C., Jr. 1999. Influence of CGA-277476 on efficacy of postemergence graminicides. Weed Technol. 13:48-53.
- Smith, M. C., Shaw, D. R., and Bennett, A. C. 1999. Interaction of glyphosate rate and initial application timing on season-long weed control in Roundup Ready soybean. Proc. South. Weed Sci. Soc. 52:207.
- Smith, M. C., Shaw, D. R., and Schraer, S. M. 1999. Efficacy of soil-applied residual herbicides in Mississippi glyphosate-tolerant soybean. Weed Sci. Soc. Am. Abst. 39:7.
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Progress 07/01/98 to 12/01/98
Outputs
Glyphosate-tolerant soybean systems provided better economic returns than conventional herbicide systems, except when lower-yielding cultivars were selected or when weeds such as hemp sesbania were marginally controlled. Glufosinate was highly effective on a wide range of grass and broadleaf weeds. The soil-applied herbicides imazaquin, chlorimuron plus metribuzin, and sulfentrazone plus chlorimuron enhanced control of pitted morningglory and hemp sesbania over glyphosate alone. Tank-mixing glyphosate with acifluorfen, fomesafen, cloransulam, and imazapic at reduced rates was also beneficial in improving control of these weeds. Reducing soybean row spacing improved soybean competitiveness, which reduced the need for a second postemergence application of glyphosate, as was true when soybean seeding rates were increased. Glyphosate was most effective in reducing populations of the perennial weeds redvine and yellow nutsedge when three applications were used, or when two
applications were used at higher rates or separated by more time between applications. Aerial multispectral images were used in an attempt to determine reflectance differences between pitted morningglory, entireleaf morningglory, common cocklebur, and sicklepod. Discriminate analysis indicated a high degree of correct classification for pitted morningglory and entireleaf morningglory, with greater error associated with common cocklebur and sicklepod classifications. Spatial variability in pitted morningglory populations were partially described by the soil properties pH, K, and Na content.
Impacts
(N/A)
Publications
- ASKEW, S. D., J. E. STREET, D. R. SHAW. 1998. Herbicide combinations for red rice (Oryza sativa) control in soybean (Glycine max). Weed
- ELLIS, J. M., D. R. SHAW, W. L. BARRENTINE. 1998. Soybean (Glycine max) seed quality and harvesting efficiency as affected by preharvest weed populations. Weed Technol. 12:166-173.
- SCOTT, R .C. D. R. SHAW. 1998. Effect of SAN 582 on sethoxydim efficacy in johnsongrass (Sorghum halepense) and soybean (Glycine
- SCOTT, R. C., D. R. SHAW, W. L. BARRENTINE. 1998. Glyphosate tank mixtures with dimethenamid for burndown or postemergence applications in glyphosate-tolerant soybean. Weed Technol.12:23-26.
- SCOTT, RC ET AL.1998.Spray adjuvant, formulation, and environ. effects on synergism from POST-applied tank mixtures of SAN 582H with fluazifop-p, imazethapyr, and sethoxydim. Weed Technol.12:463-469
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