US data reveals UK GM trials unscientific

(the internet address of this page is www.btinternet.com/~nlpwessex/Documents/gmtrialsscience.htm )

"The results of this research indicate that cultivation or residual herbicide combinations are essential for consistent season-long weed control with glufosinate or glyphosate"
WSSA Abstracts, 1999, Ref: 112

"The results of field experiments showed that a weed management strategy with glufosinate must include multiple applications, residual herbicides or mechanical control"
WSSA Abstracts, 1998, Ref: 1.14

"...applications of residual herbicides....extends the time period in which glyphosate can be effectively applied"
WSSA Abstracts, 1998, Ref: 1.16

The scientific paper abstracts below published by the Weed Science Society of America reveal the extent to which the UK farm-scale trials on GM herbicide resistant crops are likely to be a less than meaningful exercise.  These papers demonstrate a great deal about the realities of such crops in practice, rather than the largely theoretical models regarding their usage which underpin the UK trials. The American experience suggests that there is little overlap between biotechnology theory and actual agricultural practice in this sphere.

The original hope was that the introduction of herbicide resistant genetically modified crops would allow substantial falls in herbicide applications - a single application of something like Monsanto's Roundup was all that many assumed would be necessary to manage crop weeds.

Unfortunately little or no independent agronomic data on the use of this technology was provided to American farmers prior to its commercial introduction [1].  In practice the realities of the technology have proven to be rather different now that several seasons experience with it are under US farmers belts and independent agronomists have finally been given a chance to take a closer look at it.

For single applications of glyphosate or glufosinate to give desired levels of weed control it is usually necessary to delay spraying until as much as possible of the weed population has germinated. This can mean leaving relatively long periods of uncontrolled growth for early germinating weeds, ultimately leading to losses in crop yields.

Not surprisingly, therefore, many agronomists in the US (now with the benefit of a few years experience of growing transgenic herbicide resistant crops) are now advising multiple applications of these herbicides - or their use in conjunction with other herbicides to achieve longer periods of weed control - in order to preserve crop yield potential.

Clearly there is still significant variation according to site and season as to what is most effective. However, except for cases where there are particularly favourable weed pattern conditions, single dose applications of chemicals like Roundup without assistance from any other chemical formulations appear to becoming predominantly a thing of the past in the US.  This is to such an extent that some studies no longer even attempt to include single application scenarios at all within their trials.

Unless the farm-scale trials in the UK take the practical agronomic realities of the technology into account much of the results they produce will have little or no relevance to the assessment of  the actual environmental impact of these novel herbicide resistant crops, if and when they are finally put to commercial use in the UK.

Without taking such factors into account it increasingly looks as if the millions of pounds worth of UK taxpayers money being spent on the farm-scale trials is going to be wasted. This stems from the basic error of failing to establish the likely agronomy of these crops once in commercial use before designing the scientific protocols for the environmental assessment that the farm-scale trials are supposed to be.

The situation is made doubly worse by the fact that the industry body 'SCIMAC' is in charge of setting the chemical regimes that are being tested on GM crops in the UK trials. With its strong representation from the biotechnology sector there is little incentive for SCIMAC to present agro-ecological scenarios which might prove 'unhelpful' to the eventual approval of the technology, even if such scenarios are the ones which will eventually apply in practice in order to maximise crop financial performance.

It is also interesting to note from the US studies the levels of active ingredient ('ai') used in the various applications of glyphosate and glufosinate (up to 1.12kg/ha or more in a single application in the case of glyphosate). This is particularly so given that evidence has recently emerged that the use of recommended rates of glyphosate in herbicide resistant crops may be increasing the incidence in soils of Fusarium - a disease causing fungal pathogen [2].  Such disruptions to soil biology may have long term consequences for the sustainability of soil fertility [3]. 

There are also indications from the US that the introduction of such technology may lead to 'weed shift' necessitating the use of additional herbicide types [4], [5], [6].

In the US many farming areas have little biodiversity left and therefore the impact of introducing new herbicide regimes on the local ecology may be of lesser concern. In the UK, however, there is still much more left to lose.

21 February 2001

NATURAL LAW PARTY WESSEX
nlpwessex@bigfoot.com
www.btinternet.com/~nlpwessex

[1] See article on why agronomic data was kept from US farmers when the technology was introduced www.btinternet.com/~nlpwessex/Documents/gmlemmings.htm

[2] Progressive Farmer, January 03, 2001 http://www.biotech-info.net/soil_fungus.html

[3] 'Dismantling the myth of genetics as the principal constraint on responsible global agricultural production' http://www.btinternet.com/~nlpwessex/Documents/geneticsmyth.htm

[4] WSSA Abstracts below: 2000 (51); 2000 (328); 1999 (336)

[5] Successful Farming, February 15, 2001 http://www.agriculture.com/default.sph/AgNews.class?FNC=topStoryDetail__ANewsindex_html___44941___1

[6] Progressive Farmer, June 12, 2000 http://www.biotech-info.net/weed_shift.html

[Addendum April 2001: see also 'UK GMO Field Trials - A Tragi-Comedy of Errors', ISIS Report March 15, 2001
http://www.i-sis.org/AEBCnorwich-pr.shtml for more information on scientific deficiencies of farm scale trials]

WSSA ABSTRACTS 2000 Meeting of the Weed Science Society of America, Volume 40, 2000 [extracts]

Barnyardgrass ( Echinochloa crus-galli) control in Liberty-link rice. B.J. Williams*, Northeast Res. Station, St. Joseph, LA; S.D. Linscombe, Rice Res. Station, Crowley, LA.

Barnyardgrass control in Liberty-link (glufosinate tolerant) rice was evaluated from 1997 to 1999 at the Northeast Research Station near St. Joseph, LA on a Sharkey clay. Glufosinate tolerant rice was drill seeded at 140 kg/ha in rows 19 cm apart. Permanent floods were established 4 to 5 weeks after planting each year. Nitrogen at 126 kg/ha, in the form of prilled urea, was applied just before permanent flood. All treatments received an additional 42 kg/ha of nitrogen at panicle initiation. Herbicide treatments were applied in 140 L/ha of water using a C02 pressurized backpack sprayer to plots measuring 2 m by 4.5 m. Herbicide treatments were arranged in randomized complete blocks with three replications. Single applications of glufosinate at 0.56 kg ai/ha applied early postemergence and postemergence controlled barnyardgrass 80 and 87%, respectively. Barnyardgrass control with 0.28 and 0.41 kg ai/ha glufosinate was less than 75%, regardless of application timing. Glufosinate at 0.41 kg ai/ha applied postemergence and middle postemergence following delayed preemergence applications of 1.12 kg ai/ha pendimethalin controlled bamyardgrass 93 and 90%, respectively. Bamyardgrass control was only 70 and 85% when glufosinate was applied early postemergence and late postemergence following pendimethalin, respectively. Rice yields were also maximized when glufosinate was applied either postemergence or middle postemergence following pendimethalin. In another study, sequentially applying 0.28 kg ai/ha of glufosinate (early postemergence/late postemergence) controlled bamyardgrass 92% and maximized rice yield. Glufosinate rates above 0.28 kg ai/ha did not improve bamyardgrass control or rice yield when applied sequentially. Research indicates that sequential applications of glufosinate at 0.41 to 0.56 kg ai/ha will be required to control red rice (Oryza sativa). This research indicates that glufosinate programs designed to manage red rice will also control bamyardgrass. However, conventional rice herbicides may improve bamyardgrass control, bwilliams@agctr.lsu.edu (1)

The effect of row spacing, plant population, and time of weed removal on yield of glyphosate-tolerant soybean (Glycine max.). C.J. Levkulich*, M.M. Loux, andA.F. Dobbels, Ohio State Univ., Columbus.

Field studies were conducted in 1998 and 1999 to determine the effect of row spacing, soybean density, and time of weed removal on yield of glyphosate-tolerant soybean. Treatments included all possible combinations of row spacing (19 and 38 cm), soybean density, (256,984 and 504,084 plants ha-1 ), and timing of glyphosate application (7, 15, 23, 30 cm giant foxtail (Setaria faberi Herrm.). Additional treatments were included where the initial application at 7 or 15 cm was followed by a subsequent application approximately 2 to 3 weeks later. The glyphosate for all initial applications was 0.84 kg ae ha-1, and 0.63 kg ae ha-1 for subsequent applications. Light intensity was measured at soil level to determine the effect of row spacing and plant population on the time of canopy closure. Soybean canopy development was most rapid for the combination of 19 cm rows and high soybean density in 1998. At one site, increased soybean density and reduced row spacing resulted in increased yield. At the second site, yield increased as row spacing increased. Row spacing and soybean density had little effect on the control of giant foxtail. At one location, all treatments provided 100% weed control. Soybean yield was reduced only when weeds were allowed to reach a height of 30 cm before glyphosate application. Treatments at the second site providing at least 90% control included late post applications (weeds 23 cm or taller) and multiple applications of glyphosate. However, there was a trend for lower soybean yield in any treatment where glyphosate was applied only once. At the second site, yield was reduced when weeds were 15 cm or taller at the time of application. Weed control and yield differences between sites were partly due to a difference in planting date. Results from the 1999 studies will be presented also. (9)

Impact of continuous glyphosate use on weed populations in a corn-soybean rotation. M.W. Marshall, K. Al-Khatib, and L. Maddux, Kansas State Univ., Manhattan.

Weed populations respond to any selection pressure by shifting to more adapted biotypes. With the introduction of glyphosate tolerant crops, glyphosate use has increased dramatically. This study was conducted to evaluate the effects of different herbicide treatments on weed populations. Plots were overseeded with large crabgrass (Digitaria sanguinalis), ivyieaf momingglory (Ipomoea hederacea), and vel-vetleaf (Abutilon theophrasti). Herbicide treatments in corn were atrazine+flumetsulam+meto-lachlor(1.68 kg ha-1) 0 days after planting (DAP) followed by atrazine+bromoxynil (0.84 kg ha-1) 30 DAP, glyphosate (1.12 kg ha-1) 30 DAP, glyphosate (1.12 kg ha-1 at 30 DAP followed by glyphosate (0.84 kg ha-1) 45 DAP, atrazine+flumetsulam +metolachlor (1.68 kg ha-1) 0 DAP followed by interrow cultivation 30 DAP at a depth of 10 cm, glyphosate (0.84 kg ha-1) at 24 DAP followed by interrow cultivation 30 DAP at a depth of 10 cm, atrazine+flumetsulam+metolachlor (1.68 kg ha-1) at 0 DAP followed by glyphosate (1.12 kg ha-1) 30 DAP. Soybean treaments were the same except for the residual herbicide treatments and the standard post-emergence treatment. Residual herbicide treatment was sulfentrazone+chlorimuron+metolachlor (0.55 kg ha'1) and standard (non-glyphosate) was bentazon+acifluorfen+chloransulum-methyl+COC (1.03 kg ha'). There was an increase in ivyieaf momingglory and large crabgrass populations under non-residual herbicide treatments including glyphosate. 13.43 and 14.23 plants m-2 in both locations compared with 1.86, 1.73, and 1.07 plants m-2 for residual herbicide treatments. Predominance of morning-glory in the plots showed that with increasing use of glyphosate, a shift to species that are not easily controlled will occur. Therefore, combining a residual herbicide program with glyphosate will greatly improve performance and help minimize population shifts in the field. (51)

  Efficacy of diphenylether or ALS-inhibiting broadleaf herbicides tank-mixed with glyphosate. W.B. Henry*, D.R. Shaw, and T.H. Koger, Miss. State Univ., Miss. State.

Tank mixtures of full and 1/2 rates of diphenylether herbicides or ALS-inhibiting herbicides with various glyphosate rates were evaluated in 1998 and 1999 at Starkville and Raymond, MS. Weeds examined were pitted momingglory, entireleafmomingglory, and hemp sesbania. Diphenylether herbicides included fomesafen, acifluorfen and lactofen. For these treatments metolachlor was applied as a blanket PRE. ALS-inhibiting herbicides included imazaquin, imazamox, cloransulam, chlo-rimuron, CGA-277476 and cloransulam+ flumetsulam. A sequential application of glyphosate at 0.84 kg ai ha-1 (SWAP) and 0.56 kg ha-1 (5WAP) was the standard to which the tank mixtures were compared. Early season weed control was measured two to four weeks after the initial application. At both locations and in both years, single applications of either diphenylether or ALS-inhibiting herbicide tank-mixed with 0.42 kg ha-1 glyphosate provided control equal to, and at times better than, sequential applications of glyphosate alone. For instance, in 1999 at Starkville sequential applications of glyphosate controlled entireleafmomingglory, pitted momingglory and hemp sesbania 70%, 74% and 73%, respectively. Diphenylether herbicides at 1/2X tank-mixed with 0.42 kg ha~1 glyphosate controlled entireleaf morningglories, pitted mornngglories, and hemp sesbania as follows: fomesafen, 84%, 89%, and 100%; acifluorfen, 83%, 88%, and 100%; lactofen, 86%, 86% and 100%. Late season weed control was measured 13-15 weeks after appli-cation. At Starkville, 1/2 rates of both fomesafen and lactofen tank-mixed with 0.42 kg ha-1 glyphosate continued to control late season entireleaf morningglories equal to sequentially applied glyphosate. A full rate of acifluorfen was required for comparable control. At Raymond 1/2 rate of fomesafen and acifluorfen were sufficient, while a full rate of lactofen was needed. Full rates ALS-inhibiting herbicides tank-mixed with 0.42 kg ha-1 glyphosate were needed to control entire leaf and pitted momingglories late season at the same level as glyphosate alone. (129)

Determining the critical period of weed management in glyphosate-tolerant corn: results of a two-year multi-state study. S.A. Gower*, M.M. Loux, and J. Cardina, The Ohio State Univ., Columbus; P. Sprankle, N.J. Probst, M.W. Bugg, and M. Spaur, Monsanto Company, St. Louis, MO; M.D.K. Owen, Iowa State Univ., Ames; T.T. Bauman, Purdue Univ., West Lafayette, IN; S.E. Hart, Univ. of Illinois, Urbana; R.S. Currie, Kansas State Univ. Res.-Extension Center, Garden City; D.L. Regehr, Kansas State Univ., Manhattan; W.W. Witt and C.H. Slack, Univ. of Kentucky, Lexington; J.J. Kells, Michigan State Univ., East Lansing; W.G. Johnson, Univ. of Missouri, Columbia; W.S. Curran, Penn State Univ., Univ. Park; and R.G. Harvey, Univ. of Wisconsin, Madison.

A field study was conducted in 1998 and 1999 at over 30 locations throughout the North Central region to determine the effect of time of weed removal on weed control and yield of glyphosate-tolerant corn. Herbicide treatments included the following: glyphosate applied once when giant foxtail (Setaria faberi Herrm.) was 5, 10, 15, 23, or 30 cm tall; glyphosate applied when giant foxtail was 5, 10, or 15 cm tall followed by a second application; and weed-free and untreated controls. The glyphosate rate was 0.84 and 0.6 kg ae ha~1 for initial and subsequent applications, respectively. In 1998, there was a significant effect of herbicide treatment on yield at approximately one-half of the sites when weed reinfestation was prevented after initial application. Yield loss was observed most often among these sites when weeds were allowed to reach a height of 15 cm prior to herbicide application, but this ranged from 10 to 30 cm across all sites. Average corn yield at the 5, 10, 15, 23, and 30 cm timings was 101, 99, 93, 93, and 80 percent of the weed-free control, respectively. The reduction in corn yield with increasing weed size was described by a quadratic regression equation. Average weed control for these treatments was greater than 90 percent for grass and broadleaf weeds, but was occasionally as low as 70 percent due to late emergence of annual grasses and Amaranthus species or difficulty in controlling Ipomoea species. Weed control and corn yield were considerably more variable in 1998 where glyphosate was applied only once. Most effective and consistent annual grass control occurred when glyphosate was applied to grasses at least 15 cm in height. Broadleaf control was more variable than grass control across all timings, but averaged 90 percent or greater when applied to weeds 10 to 30 cm tall. For a single application of glyphosate, average corn yield at the 5, 10, and 15 cm timings was 91, 96, and 94 percent of the weed-free control, respectively. (260)

  Pitted morningglory (Ipomoea lacunosa) and hemp seshania (Sesbania exaltata) interference in drilled soybean (Glycine max) as affected by cultural practices and glyphosate timing. J.K. Norsworthy* and L.R. Oliver, Univ. of Arkansas, Fayetteville.

With increased glyphosate use, pitted morningglory and hemp sesbania are becoming more common in soybean fields throughout the southern United States. Field studies were conducted to evaluate soybean seeding rate and glyphosate use on the degree of interference of pitted morningglory and hemp sesbania in drilled soybean. Soybean was more competitive as soybean population increased, resulting in reduced weed biomass and seed production and often increased soybean yield. Pitted morningglory treated with 1.12 kg ai/ha glyphosate at V5 had a 2.7-fold reduction in photosynthetic acitivity two weeks after treatment compared to untreated plants. Late-season shading of soybean by untreated hemp sesbania at 16 plants/m2 reduced soybean photosynthetic activity, but glyphosate-treated hemp sesbania had no effect on soybean photosynthesis. Untreated hemp sesbania intercepted less light as soybean density increased, evidence of increased soybean competitiveness at higher densities. Hemp sesbania and pitted morningglory biomass accumulation increased minimally following glyphosate treatment; however, plants were able to produce seed which could increase the proportion of these species within the soil seedbank, resulting in a weed spectrum shift under continued glyphosate use. jnorswo@comp.uark.edu (328)

WSSA ABSTRACTS
1999 Meeting of the Weed Science Society of America, Volume 39, 1999 [extracts]

(7) Efficacy of soil-applied residual herbicides in Mississippi glyphosate-tolerant soybean. M. C. Smith*, D. R. Shaw, and S. M. Schraer. Miss. State Univ., Miss. State.

Experiments were conducted in 1997 and 1998 to compare weed control systems containing soil-applied herbicides followed by a single glyphosate application to a sequential glyphosate treatment standard. Soil types included a silty clay loam near Brooksville, MS, in 1997 and 1998; a very fine sandy loam near Newton, MS, in 1997 and 1998; and a silt loam near Raymond, MS, in 1998. In each experiment, soil-applied treatments included pendimethalin + imazaquin, pendimethalin + metribuzin + chlorimuron, pendimethalin -+- sulfentrazone -t- chlorimuron, and metolachlor + flumetsulam. All soil herbicides were applied at full-labeled rates according to soil type. All soil-applied treatments were followed with a single application of both 0.56 and 0.84 kg ai/ha glyphosate at 3 to 5 weeks after planting. All treatments were compared to sequential applications of 0.84 followed by 0.56 kg/ha glyphosate. Averaged over all experiments and soil-applied herbicide treatments, late-season pitted momingglory (Ipomoea lancunosa L.) and sicklepod [Senna obtusifolia (L.) Irwin and Bamey] control ranged from 67 to 70%, and was not affected by glyphosate rate. When data at Brooksville were pooled, soil-applied treatments followed by glyphosate controlled pitted momingglory and sicklepod approximately 54% and 63%, respectively, which was equal to the sequential glyphosate standard. When pooled, pitted momingglory control at Newton averaged 82% and did not differ between any treatment. At Newton in 1997, sicklepod was controlled no more than 64% with glyphosate following pendimethalin + imazaquin, pendimethalin + metribuzin + chlorimuron, or pendimethalin + sulfentrazone + chlorimuron. However, metolachlor + flumetsulam followed by glyphosate controlled sicklepod 90% and equaled the glyphosate standard. At Newton in 1998, all treatments controlled sicklepod at least 86%. At Raymond, pendimethalin + sulfentrazone + chlorimuron followed by glyphosate controlled pitted momingglory 89%, compared to less than 55% control with all other treatments including the sequential glyphosate standard.

(15) BAY FOE 5043 & metribuzin: Early-season preemergence weed control in transgenic soybean or ahead of other planned postemergence herbicide applications. B. D. Philbrook*, J. R. Bloomberg, J. P. Sleesman, and I. Dannenberg, Bayer Corp., Kansas City, MO.

Postemergence weed control can be difficult due to various constrictions on the window of application opportunities. Unfavorable weather patterns, intense weed pressure, multiple weed flushes, multi-layered weed canopies, rapidly closing crop canopies and other factors can all inhibit the ability to deliver an adequate postemergence application at the proper timing. These barriers do not account for insensitive weed species or stages, nor required retreatments. BAY FOE 5043 & metribuzin (1:1.5 ratio) is a new soil-applied herbicide being offered by Bayer Corporation to provide activity on many grasses and broadleaf weeds in soybeans. Field tests were conducted throughout the United States in 1997 and 1998 to evaluate and demonstrate the utility of BAY FOE 5043 & metribuzin soil-applied used in conjunction with a planned postemergence herbicide program. At 0.38 to 0.72 kg ai/ha, it provided weed control for the first four to six weeks after application. This early season weed control reduced the severity of weed competition with the crop, and allowed for a wider application window prior to the planned postemergence herbicide application. It also assisted in maintaining remaining weeds or newly emerging weeds at a more uniform height and canopy density, which allows for more complete spray coverage and potentially improved control with the postemergence herbicides.

(17) The effect of row spacing, plant population, and time of weed removal on yield of glyphosate-tolerant soybean. C. J. Levkulich* and M. M. Loux, Ohio State Univ., Columbus.

Field studies were conducted in 1998 to determine the effect of row spacing, soybean population and density, and time of weed removal on yield of glyphosate-tolerant soybean. Treatments included all possible combinations of row spacing (19 and 38 cm), soybean density (256,984 and 504,084 plants ha -1), and timing of glyphosate application (7, 15, 23, and 30 cm giant foxtail [Setaria faberi Herrm.]). Additional treatments were included where the initial application at 7 or 15 cm was followed by a subsequent application approximately 3 weeks later, or where application of a preemergence herbicide preceded glyphosate application at 7 and 15 cm. The glyphosate for all initial applications was 0.84 kg ai ha ' , and 0.63 kg ai ha ' for subsequent applications. At one site, all treatments provided near 100% weed control. Treatments at the second site providing at least 90% control included late post applications (weeds 23 cm or taller), multiple applications of glyphosate, and treatments where glyphosate was applied following a preemergence herbicide. The difference in weed control between sites was due to an earlier planting date and higher weed density at the second site. The effect of treatments on soybean yield will be discussed.

(111) Determining the critical period of weed interference in glyphosate-tolerant corn: results of a multi-state study. S. A. Gower* and M. M. Loux, Ohio State Univ., Columbus; J. Carolina, Ohio State Univ., Wooster; P. L. Sprankle and N. J. Probst, Monsanto Co., St. Louis, MO.

Until recently, the availability, effectiveness, and economics of total postemergence weed control systems in corn have been limited. With the advent of glyphosate-tolerant corn, producers now have a new tool for postemergence weed management in corn. However, there is some question as to how long weeds can coexist with corn before crop yield is affected. Also, data are lacking to accurately determine the optimum application timing of total postemergence herbicide programs in corn. A multi-state study was conducted with glyphosate-tolerant corn to determine the effect of duration of weed interference on corn yield. Although weed populations varied among sites, the height of giant foxtail (Setaria faberi Herrm.) was used to determine application timing. Treatments included single applications of glyphosate when giant foxtail was 5, 10, 15, 23, and 30 cm in height. Other treatments consisted of an application when giant foxtail was 5, 10, and 15 cm in height followed by a second application two weeks later. The glyphosate rate was 0.84 kg ai ha-1 in all treatments. Multiple applications of glyphosate or single applications when giant foxtail was at least 15 cm tall generally resulted in the most effective weed control. Effect of application timing on corn yield will be discussed.

  (112) Weed control strategies in glufosinate resistant and glyphosate resistant corn. B. E. Tharp*and J. J. Kells, Michigan State Univ., East Lansing.

Glufosinate and glyphosate are now being used for weed control in corn. The greatest limitation of these herbicides is their lack of residual herbicidal activity in soil. Field trials were conducted at Michigan State University in 1996, 1997, and 1998 to determine the effect of cultivation and residual herbicide combinations on weed control in glufosinate resistant and glyphosate resistant corn. Weed control from postemergence applications of the monoammonium salt of glufosinate and the isopropylamine salt of glyphosate was often improved when cultivated 10-14 days following herbicide application. Herbicide combinations consisted of: i) preemergenceapplications of atrazine, acetochlor , metolachlor, or pendimethalin followed by a postemergenceapplication of either glufosinate or glyphosate; and ii) post emergence tank mixtures of glufosinate and glyphosate with atrazine, acetochlor, metolachlor, or pendimethalin. When the residual herbicides were applied in sequential combinations or in tank mixtures the control of most annualweed species was improved as compared to glufosinate and glyphosate applied alone. The results of this research indicate that cultivation or residual herbicide combinations are essential for consistent season-long weed control with glufosinate or glyphosate.

(113) Utilization of herbicide resistant corn for woolly cupgrass (Eriochloa villosa) management. D. W. Lycan* and S. E. Hart, Univ. of Illinois, Urbana.

Field studies were conducted at two locations in Livingston County, IL during 1997 and 1998 to develop, evaluate, and compare woolly cupgrass management systems in herbicide resistant corn utilizing nicosulfuron, sethoxydim, imazethapyr + imazapyr, glufosinate, and glyphosate. These herbicides were applied at a POST timing alone and following soil-applied acetochlor, which was applied at 2020 g ai/ha. Sequential treatments of sethoxydim, glufosinate, and glyphosate were applied at POST and LATE POST timings. All applications of nicosulfuron, sethoxydim, glufosinate, and glyphosate were made at 35, 210, 300, and 630 g ai/ha, respectively. Imazethapyr + imazapyr were applied at 45 + 15 g ai/ha, respectively. In 1997, single postemergence applications of nicosulfuron, sethoxydim, imazethapyr -+- imazapyr, glufosinate, and glyphosate provided averages of 88, 91, 88, 87, and 96% control of woolly cupgrass, respectively, at 30 DAT, Control of woolly cupgrass with nicosulfuron, sethoxydim, imazethapyr + imazapyr, and glufosinate was maximized by either sequential postemergence applications or soil-applied acetochlor followed by a postemergence application of the respective herbicide. All treatments that included glyphosate provided at least 96% control of woolly cupgrass. In 1998, single postemergence applications of nicosulfuron, sethoxydim, imazethapyr + imazapyr, glufosinate, and glyphosate provided averages of 76, 86, 83, 87, and 91% control of woolly cupgrass, respectively. at 30 DAT. In 1998, soil-applied acetochlor preceding postemergence herbicides did not improve control as compared to single postemergence applications, due to excessive rainfall throughout the growing season.

  (114) Evaluation of weed control systems on Roundup Ready corn using precision agriculture technologies. E. S. Oyarzabal*, M. W. Bugg, J. A. Laskowski, N. J. Probst, S. P Lynch, Monsanto Co., Des Moines, IA, Indianapolis, IN, and St. Louis MO; and B. Herr, Fields of Vision, Greensburg, IN.

The availability of transgenic corn [hybrids resistant to Roundup (glyphosate)] herbicide will allow new weed control alternatives. Several large strip trial experiments were conducted in Iowa and Indiana with the objective of studying weed control systems on Roundup Ready corn. Agronomic information such as soil type, soil nutrients (N-N03, P, K, pH, Ca, Mg, OM, CEC), weed control, and yields were collected with the help of precision agriculture technologies such as GPS, grid soil sampling, yield monitors and remote sensing devices. Calibrated commercial equipment was used to apply all the treatments. The main systems tested were: a) a residual herbicide followed by conventional post emergence treatments, b) a residual herbicide followed by glyphosate, and c) a total post emergence program using glyphosate sequentially. Conventional ANOVA analysis and statistical analysis that account for spatial variation were used to detect weed control and yield differences between treatments. No differences in yield were observed in these experiments. The systems that included glyphosate demonstrated better weed control than the conventional treatment.

(116) Yellow nutsedge (Cyperus esculentus L.) control with glyphosate and glyphosate tankmixtures. K. A. Nelson* and K-. A. Renner, Michigan State Univ., East Lansing.

Field studies were conducted in 1997 and 1998 to evaluate yellow nutsedge control withglyphosate, acetolactase-inhibiting herbicides, and glyphosate tank mixtures. Glyphosate at 840 g ae ha-1 (formulated as Roundup Ultra®) plus ammonium sulfate (AMS) at 20 g L -1 provided 53% yellow nutsedge control and reduced yellow nutsedge dry weight by 62% 56 days after treatment (DAT). Yellow nutsedge control, height, or dry weight was not affected when 0.25% v/vnonionic surfactant, 1.3% v/v crop oil concentrate, or 1.0% v/v methylated seed oil was added to glyphosate plus AMS. Halosulfuron at 35 g ai ha-1 , chlorimuron at 12 g ai ha-1, andimazethapyr/imazapyr at 62 g ai ha-1 provided 97, 86, and 74% control, respectively. Tankmixtures with 840 g ha-1 glyphosate did not influence control. Imazethapyr at 70 g ai ha-1, imazamox at 45 g ai ha-1 , clorasulam at 17.5 g ai ha-1, rimsulfuron at 17.5 g ai ha-1, andpyrithiobac at 70 g ai ha'1 provided 39 to 58% yellow nutsedge control. Yellow nutsedge dryweight reduction was halosulfuron = chlorimuron > pyrithiobac >_ glyphosate =imazethaypr/imazapyr = imazethapyr = cloransulam >_ rimsulfuron >_ imazamox 56 DAT. Tankmixtures of imazethapyr, imazamox, cloransulam, and rimsulfuron with glyphosate reduced yellow nutsedge dry weight and increased control compared to glyphosate or these acetolactase-inhibiting herbicides applied alone.

(323) Weed management strategies for glyphosate-tolerant cotton under ultra narrow row conditions. W. T. Molin*, USDA-ARS, Stoneville, MS.

Field experiments were conducted in 1998 at the Southern Weed Science research farm to evaluate eight different weed management systems for control of upright spotted spurge (Euphorbia maculata L.), prickly sida (Sida spinosa L.) and hemp sesbania (Sesbania exaltata (Raf) Rybd. ex A. W. Hill). Trifluralin at 1.12 kg ai ha-1 PPI was applied to all plots. The treatments included fluometuron, fluometuron + glyphosate, fluometuron + pyrithiobac (PRE), fluometuron + pyrithiobac (POST), glyphosate, split application of glyphosate, pyrithiobac (PRE) + glyphosate, and fluometuron + pyrithiobac (PRE) + glyphosate. Fluometuron was applied at 840 g ai ha-1 , pyrithiobac at 22 g ai ha-1 PRE or POST, and glyphosate at 840 g ai ha-1 POST. Split applications of glyphosate controlled prickly sida and reduced spurge by 76%. Pyrithiobac (PRE) + glyphosate reduced prickly sida by 85%. There were no significant differences among treatments for control of hemp sesbania although split applications of glyphosate reduced hemp sesbania by 45%. There were no significant differences among the eight treatments for the number of bolls m-2 or lint yields; although, the highest yields were for fluometuron + glyphosate.

  (336) Weed shifts: potential implications for Roundup Ready cropping systems. M. J. Horak*, G. M. Dill, and R. W. Krueger, Monsanto Co., St. Louis, MO.

Weed shifts are changes in the composition of weed communities in response to manmade or natural changes or stresses imposed on a weed - crop community. Weed shifts are not a new phenomenon but rather have occurred throughout history. As man has tried to modify the environment for the production of desired species (turf, ornamentals, horticultural and agronomic crops, forest products) shifts have occurred in associated weed communities - those species not able to adapt to the change become less frequent while those which do adapt survive and increase in frequency. Weed shifts are known to occur within weed populations and communities. Observed changes in weed populations and communities can be short term or immediate fluctuations in response to transient changes in agriculture (cropping sequence, cultivation regime, or herbicide application) or may represent long term successional changes. With the introduction of herbicide resistant crops there has been a renewed interest in weed shifts as a result of the use of these technologies. The purpose of this presentation is to discuss the potential for shifts within weed populations and communities, discuss weed characteristics that allow for shifts, discuss selection phenomenon, and avoidance strategies, in the context of Roundup Ready cropping systems.

1998 Meeting of the Weed Science Society of America, Volume 38, 1998 [extracts]

1.11 Preemergence herbicide systems in Roundup-Ready® soybean. C. R. Medlin*, D. R. Shaw, and A. Rankins, Jr., Mississippi State University, Mississippi State.

Field experiments were conducted in 1997 at the Coastal Plain Branch Experiment Station, Newton, MS, and the Black Belt Branch Experiment Station, Brooksville, MS, to evaluate PRE herbicides followed by glyphosate in Roundup-Ready® soybean. PRE herbicide systems evaluated were pendimethalin applied