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Weed Technology 2007 21:753-758
 

Weed Technology 2007 21:753-758

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Reducing Weed Seed Rain with Late-Season Glyphosate Applications

Reducing Weed Seed Rain with Late-Season Glyphosate Applications

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    Weed Technology 2007 21:753-758 Weed Technology 2007 21:753-758 Document Transcript

    • Weed Technology 2007 21:753–758 Reducing Weed Seed Rain with Late-Season Glyphosate Applications Chad E. Brewer and Lawrence R. Oliver* Field trials were established in Fayetteville, AR, to determine the effects of glyphosate on biomass and seed production of spurred anoda, entireleaf morningglory, hemp sesbania, and Florida pusley. Inconsistent control of these species by glyphosate allows them to enrich the soil seedbank. Glyphosate rates of 0.42, 0.84, and 1.68 kg ae/ha were applied at 3, 6, and 9 wk after emergence (WAE) and were compared with a nonsprayed control. Spurred anoda seed production was reduced 99.9% by glyphosate at 1.68 kg/ha averaged over application timings and 99.7% by glyphosate applied at 6 WAE averaged over rates. Entireleaf morningglory seed production was reduced 100% by glyphosate at 1.68 kg/ha at 3 WAE and . 93% by the same rate applied at 6 or 9 WAE. Hemp sesbania seed production was reduced 100% by glyphosate at 1.68 kg/ha at 3 WAE and . 96% by glyphosate at 0.42, 0.84, and 1.68 kg/ha applied at 6 or 9 WAE. Florida pusley seed production was reduced 99.9% by glyphosate at 1.68 kg/ha averaged over application timings and 99.4% by application at 3 or 6 WAE averaged over rates. Biomass accumulation for all species was reduced most by early applications, particularly at 1.68 kg/ha. Nomenclature: Glyphosate; entireleaf morningglory, Ipomoea hederacea var. integriuscula (L.) Jacq. A. Gray IPOHG; Florida pusley, Richardia scabra L. RCHSC; hemp sesbania, Sesbania exaltata (Raf.) Cory SEBEX; spurred anoda, Anoda cristata (L.) Schlecht ANVCR.. Key words: Seed production, seedbank, species shift. The soil seedbank is the main source of all weeds present without regard for return of weed seed to the soil seedbank in production agriculture (Cavers and Benoit 1989) and (Coble and Mortensen 1992). If a weed species emerges after comprises all viable seeds present on or in the soil or the the critical weed-free period or if weed density is not sufficient associated litter (Simpson et al. 1989). Many weed species to cause yield or quality reduction, these weeds may be left to have emerged as problem weeds in glyphosate-based herbicide reproduce and enrich the soil seedbank. Enrichment is caused systems. Spurred anoda control by glyphosate varies from 80 by weed seed rain, which is the reproduction and dispersal of to 100% (Richardson et al. 2004). Entireleaf morningglory weed seed from the parent plant (Radosevich et al. 1997). control can be as low as 64% (Starke and Oliver 1998). Weed seed rain effects were found to be a primary driving Glyphosate rate and timing significantly influenced the force of seedbank density for wild oat (Avena spp,) and wild control of both hemp sesbania and entireleaf morningglory radish (Raphanus raphanistrum L.) when infesting wheat ( Jordan et al. 1997; Payne and Oliver 2000). Florida pusley is (Triticum aestivum L.). Late-season herbicide applications to another problem weed in glyphosate-based weed management prevent seed production were very effective in reducing systems because it is not controlled consistently with seedbank densities ( Jones and Medd 2005). Weed seed rain glyphosate ( Johnson and Mullinix 2002). is the primary input into the seedbank (Simpson et al. 1989), Although herbicides can reduce weed interference with crop but a correlation of weed seed rain to the following season’s production, seed production by weed escapes will replenish the seedling recruitment is species specific. Webster et al. (2003) soil seedbank (Hartzler 1996, Schweizer and Zimdahl 1984). found that seedling recruitment for annual grass species was Maintaining nearly zero seed production is imperative for the dependent on the seedbank density and seed rain from the reduction of prolific seed producers in the weed seedbank previous autumn, whereas common lambsquarters (Chenopo- (Norris 1983). Menges (1987) stated that after 6 yr of weed- dium album L.) seedling recruitment was not dependent on free conditions, Palmer amaranth (Amaranthus palmeri S. seed rain when following no-till wheat production. Watts.) populations were reduced from 7.7 to 0.8 seed/100 g There have been several attempts to reduce weed seed soil, a 98% reduction in the seedbank. However, the production with herbicides. Common lambsquarters seed remaining 2% represented 18 million seed/ha, which indicates production was reduced by 2,4-D at 1.1 kg ai/ha applied that the weed-free conditions must be continued to further preanthesis by killing the plant (Fawcett and Slife 1978). In reduce the presence of Palmer amaranth seed in the seedbank. the same study, 2,4-D applied during redroot pigweed The ability to maintain 100% weed control in commercial (Amaranthus retroflexus L.) and jimsonweed (Datura strumar- production fields would be costly because of the associated ium L.) flowering reduced seed production by 74 and 100%, herbicide and labor cost. Therefore, the majority of weed respectively. However, Fawcett and Slife (1978) found that management decisions are made based on variations of an 2,4-D applied at giant foxtail (Setaria faberi L.) flowering economic threshold that deals only with the present crop increased seed production 381%. Chlorimuron at 0.28 kg ai/ ha and imazaquin at 0.28 kg ai/ha applied to sicklepod (Senna DOI: 10.1614/WT-06-145.1 obtusifolia L.) during the early bloom stage reduced seed * Senior Graduate Assistant and University Professor, Department of Crop, Soil, and Environmental Sciences, 115 Plant Science Building, University of production nearly 100% (Issacs et al. 1989). Glyphosate Arkansas, Fayetteville, AR 72701. Corresponding author’s E-mail: cbrewer@ application has been shown to reduce hemp sesbania and uark.edu pitted morningglory (Ipomoea lacunosa L.) seed production 95 Brewer and Oliver: Reducing weed seed rain with glyphosate N 753
    • Table 1. Spurred anoda, entireleaf morningglory, hemp sesbania, and Florida pusley planting and emergence dates, flower initiation date, and day length at flower initiation for 2002 and 2003 at Fayetteville, AR. Year Species Planting date Emergence date Flower initiation Day length at flower initiation 2002 Spurred anoda June 25 June 29 August 21 13 h 19 min Entireleaf morningglory June 25 June 29 August 21 13 h 19 min Hemp sesbania June 25 June 29 August 22 13 h 17 min Florida pusley July 1 July 9 August 19 13 h 24 min 2003 Spurred anoda June 16 June 20 August 11 13 h 40 min Entireleaf morningglory June 16 June 20 August 13 13 h 36 min Hemp sesbania June 16 June 24 August 20 13 h 22 min Florida pusley June 16 July 18 August 11 13 h 7 min to 98% (Norsworthy and Oliver 2002a, 2002b), common 27% sand, 61% silt, 9% clay) with a pH of 5.8 and organic purslane (Portulaca oleracea L.) 95% (Haar and Fennimore matter of , 1%. Each year the site was fertilized according to 2003), and sicklepod 86 to 100% (Barnes and Oliver 2003). University of Arkansas recommendations for corn (Zea mays Although most previous weed control research includes data L.) production, which included 224–112–112 kg/ha N– on weed seed production, most discuss seed production only P2O5–K2O (Espinoza and Ross 2003). Site preparation as a secondary aspect. included spring disking, field cultivation, and disk-hipping When annual plants begin reproduction, the floral buds in 1-m-wide rows. Following site preparation each year, and seeds become the greatest sinks because of their rapid cell spurred anoda, entireleaf morningglory, hemp sesbania, and expansion and high hormonal content (Hopkins 1999). Florida pusley seeds were hand-planted on 1-m raised beds Glyphosate accumulates in reproductive tissue because those (Table 1). Each species was thinned to a uniform density tissues act as metabolic sinks (Goughler and Geiger 1981; across the respective trials 2 wk after emergence (WAE) to Sandberg et al. 1980). Glyphosate has been shown to decrease ensure uniform initial intraspecific interference. The initial free auxin in soybean [Glycine max (L.) Merr.] and pea (Pisum plant density for each species is shown as stem number per sativum L.) (Lee 1984) and to stimulate ethylene production meter of row for the nontreated check (Tables 2–7). These in bean (Phaseolus vulgaris L.) (Abu-Irmaileh et al. 1979). densities were chosen based on the lowest emergence density Auxin and ethylene are vital in the formation of normal for each species. flowers (Swahney and Shukla 1994). Increases in free auxin A 3 by 3 plus 1 factorial treatment structure consisting of inhibit development of male floral anatomy in some species glyphosate at 0.42, 0.84, or 1.68 kg ae/ha applied at 3, 6, or 9 (Chailakhyan and Khrianin 1978) but promote it in others WAE and one nontreated check were arranged in a random- (Hamdi et al. 1987). Increases in ethylene can cause male ized complete-block design with four replications. Glyphosate sterility in Brassica species (Banga and Labana 1983). The was applied with a CO2-backpack sprayer calibrated to deliver accumulation of glyphosate in the reproductive tissue has 94 L/ha. Each plot consisted of a single strip of plants 2 m caused decreased pollen viability and increased distance long with 1-m alleys between plots on top of raised 1-m-wide between the anther and stigma in cotton (Gossypium hirsutum beds. Each replication was planted on a single 37-m row, and L.) (Pline et al. 2003). Clay and Griffin (2000) found that both adjacent rows were fallow to reduce the impact of off- glyphosate applied at weed flowering was effective in reducing target drift. This pattern was repeated across the field for all seed production of common cocklebur (Xanthium strumarium trials. L.), hemp sesbania, and sicklepod. Mixtures of glyphosate and After the first killing frost, the aboveground portion of sodium chlorate used as preharvest desiccants reduced hemp plants from the middle 1 m of each plot was hand-harvested sesbania and pitted morningglory seed production (Bennett at ground level, placed in paper bags, and allowed to air dry at and Shaw 2000). The objective of this study was to determine approximately 27 C. There was no noticeable seed shatter the effect of early-, mid-, and late-season glyphosate applications on seed rain from weeds in four distinct Table 2. Effect of glyphosate rate on end-of-season biomass and seed production morphological families. of spurred anoda at Fayetteville, AR, 2002 and 2003.a Total per meter of row Materials and Methods Glyphosate rate Biomass Stem number Seed number Experiments were conducted in 2002 and 2003 at the kg ae/ha g University of Arkansas Research and Extension Center in Nontreated 392 a 7a 16,218 a Fayetteville, AR, to determine the response of four weed 0.42 78 b 5 ab 776 b species to selected glyphosate application rates and timings, 0.84 68 b 4b 427 b with each species evaluated in a separate experiment. 1.68 11 c 2c 10 c Differences in weed species emergence dates prevented a Log-transformed data were used for analysis because of unequal treatment combining the experiments; however, the experiments were variances. Log means were separated according to Fisher’s Protected LSD, P 5 conducted concurrently. The experiments were conducted on 0.05. Detransformed means are presented with log mean separation. Means a Taloka silt loam (fine, mixed, thermic, Mollic Albaqualfs; within a column followed by same letter are not significantly different. 754 N Weed Technology 21, July–September 2007
    • Table 3. Effect of glyphosate application timing on end-of-season biomass and Glyphosate rates at or above 0.42 kg/ha decreased means for seed production of spurred anoda at Fayetteville, AR, 2002 and 2003.a,b biomass and seed production compared with the control Total per meter of row (Table 2). Seed number per meter of row was reduced 99% Glyphosate by glyphosate at 1.68 kg/ha, averaged over application timing. timing Biomass Stem number Seed number Total biomass production, averaged across rates, was reduced WAE g most by the two earliest glyphosate applications (Table 3). Nontreated 392 a 7a 16,281 a Spurred anoda total biomass and stem number were similar 3 18 b 3b 148 bc for nontreated plants and plants treated at 9 WAE. Greater 6 15 b 3b 44 c plant mortality from applications made at 3 or 6 WAE 9 158 a 5a 369 b reduced stem number compared with applications made at 9 a Log-transformed data were used for analysis because of unequal treatment WAE. All glyphosate application timings reduced seed variances. Log means were separated according to Fisher’s Protected LSD, P 5 number per meter of row compared with the nontreated 0.05. Detransformed means are presented with log mean separation. Means control (Table 3). Glyphosate application at 6 WAE reduced within a column followed by same letter are not significantly different. seed number per meter of row more than applications made at b Abbreviation: WAE, weeks after emergence. 9 WAE. These data indicate that applying glyphosate at 3 or 6 WAE causes biomass reduction and reduces seed production before plant harvest for any species. Samples were processed of spurred anoda compared with the nontreated plants. by manually removing seeds after recording stem number and However, if a plant escapes early- season control, the best total sample dry weight. To quantify seed production, seeds application timing to reduce seed production is at 6 WAE, from each sample were weighed and total seed number per which coincided with the flower initiation in this experiment. meter of row was calculated based on the average weight of These results concur with Puricelli et al. (2004), who reported 100 seeds for each sample. that glyphosate at 0.54 kg/ha achieved excellent control of Because of unequal treatment variances, data analysis spurred anoda and greatly reduced seed production. However, included logarithmic (log) transformation of individual data there was still a linear relationship between spurred anoda points. Studentized residuals were plotted for each treatment biomass and seed production. to determine whether the transformed data satisfied the Entireleaf Morningglory. The rate by timing interaction was assumption of homogeneity. Log transformed data were then significant for all parameters for entireleaf morningglory. analyzed using ANOVA by the PROC GLM function in Glyphosate applied at 1.68 kg/ha at 3 WAE reduced entireleaf SAS.1 Year was analyzed as a random variable to make broader morningglory biomass production and stem number per inferences about treatment effects (Carmer et al. 1989). meter of row compared with the nontreated control and lower Treatment log mean separation was performed by Fisher’s rates (Table 4). Seed production per meter of row of entireleaf Protected LSD at P 5 0.05. Data reported are detransformed morningglory was reduced $ 88% by glyphosate at 0.84 or treatment means that are separated according to log mean 1.68 kg/ha at 9 WAE compared with the nontreated control. separation. Glyphosate applied at 3 WAE did not reduce seed number unless glyphosate rate was 0.84 or 1.68 kg/ha, which caused plant death or severe stunting that persisted throughout the Results and Discussion season. Applications made at 6 or 9 WAE did not reduce stem Spurred Anoda. For spurred anoda, the rate by timing number per meter of row or biomass per meter of row. interaction was not significant for any response variable. Glyphosate applied at 6 WAE released the lateral buds from Table 4. Effect of rate and timing of glyphosate application on end-of-season biomass and seed production of entireleaf morningglory at Fayetteville, AR, in 2002 and 2003.a,b Total per meter of row Glyphosate rate Timing Biomass Stem number Seed number kg ae/ha WAE g Nontreated 741 a 10 a 3,890 a 0.42 3 224 ab 10 a 1,413 ab 6 447 ab 10 a 2,455 a 9 741 a 12 a 1,413 a 0.84 3 62 b 5b 371 cd 6 288 ab 12 a 617 bc 9 562 a 12 a 457 c 1.68 3 2c 1c 0e 6 186 ab 10 a 251 d 9 537 ab 12 a 263 d a Log-transformed data were used for analysis because of unequal treatment variances. Log means were separated according to Fisher’s Protected LSD, P 5 0.05. Detransformed means are presented with log mean separation. Means within a column followed by same letter are not significantly different. b Abbreviation: WAE, weeks after emergence. Brewer and Oliver: Reducing weed seed rain with glyphosate N 755
    • Table 5. Effect of rate and timing of glyphosate application on end-of-season biomass, plant density and seed production of hemp sesbania at Fayetteville, AR, 2002 and 2003.a,b Total per meter of row Glyphosate rate Timing Biomass Stem number Seed number kg ae/ha WAE g Nontreated 891 a 10 a 7,943 a 0.42 3 427 b 7c 1,148 ab 6 269 c 9 ab 155 bcd 9 525 ab 10 a 126 bcd 0.84 3 174 c 6 bc 537 bc 6 214 cd 10 ab 229 bcd 9 617 a 9 ab 302 bcd 1.68 3 3e 2d 0e 6 95 d 9 ab 49 cd 9 417 b 8 ab 28 d a Log-transformed data were used for analysis because of unequal treatment variances. Log means were separated according to Fisher’s Protected LSD, P 5 0.05. Detransformed means are presented with log mean separation. Means within a column followed by same letter are not significantly different. b Abbreviation: WAE, weeks after emergence. apical dominance, whereas entireleaf morningglory had Florida pusley were reduced equally by application of already attained maximum biomass by 9 WAE. Sublethal glyphosate at 0.42 and 0.84 kg/ha (Table 6). glyphosate applications have been observed to remove lateral Glyphosate application timing was crucial for maximum bud dormancy in soybean and pea seedlings (Lee 1984). effect on total biomass, stem number, and seed number of However, Lee (1984) found that hand removal of the apical Florida pusley (Table 7). Total biomass per meter of row was meristem did not increase indole-3-acetic acid metabolism, reduced by glyphosate applied at 3 and 6 WAE. Similarity but sublethal glyphosate application did, which reduced levels between the nontreated control and the 9 WAE applications of free indole-3-acetic acid. Reducing the amount of free indicates that the Florida pusley had reached its full size by 9 indole-3-acetic acid may alter the delicate balance of plant WAE, and any application made at this time had little effect hormones and cause changes in flower morphology and loss of on biomass accumulation. Seed number per meter of row was apical dominance. reduced by all application timings. Glyphosate applied at 3 For entireleaf morningglory, plants not controlled early in WAE caused plant death or severe stunting, whereas the season, glyphosate applications of 1.68 kg/ha at 6 or 9 applications made at 6 WAE coincided with Florida pusley WAE were necessary to reduce seed production approximately flower initiation and reduced the reproductive capability of 93%. These data indicate that a single glyphosate application the plant. The best glyphosate application timing to reduce at 1.68 kg/ha during entireleaf morningglory flowering is Florida pusley seed production . 99% was 3 or 6 WAE. sufficient to dramatically reduce seed production. Entireleaf Glyphosate was effective at reducing seed production of morningglory biomass was reduced 92% and 99.7% by spurred anoda, entireleaf morningglory, hemp sesbania, and glyphosate at 0.84 and 1.68 kg/ha, respectively, when applied Florida pusley. Although the application timings were species at 3 WAE. specific, applications made near weed flowering reduced weed Hemp Sesbania. Compared with nontreated plants, biomass seed production of each of these species with the greatest was reduced by glyphosate, except at 0.42 and 0.84 kg/ha reduction occurring at the high rate. Adequate control of these applied at 9 WAE (Table 5). Glyphosate at 1.68 kg/ha applied at 3 WAE caused the greatest reduction in seed per meter of row and biomass accumulation because of plant Table 6. Effect of glyphosate rate on end-of-season biomass, plant density, and seed production of Florida pusley at Fayetteville, AR, 2002 and 2003.a death. However, applications that did not cause plant death reduced seed production $ 93%, with the exception of Total per meter of row 0.42 kg/ha applied at 3 WAE. It was observed that Glyphosate rate Biomass Stem number Seed number applications at 6 WAE slowed the growth and development of hemp sesbania immediately before flowering, whereas kg ae/ha g applications made at 9 WAE were after flower initiation. Nontreated 389 a 7a 16,080 a Bennett and Shaw (2000) reported that glyphosate at 1.65 kg/ 0.42 76 b 5b 715 b 0.84 59 b 3 bc 315 b ha used as a preharvest desiccant reduced hemp sesbania seed 1.68 11 c 2c 10 c production by 57%. This is in contrast to the level of seed reduction seen in our study. a Log-transformed data were used for analysis because of unequal treatment variances. Log means were separated according to Fisher’s Protected LSD, P 5 Florida Pusley. The rate and timing main effects were 0.05. Detransformed means are presented with log mean separation. Means significant for all parameters. All measured parameters for within a column followed by same letter are not significantly different. 756 N Weed Technology 21, July–September 2007
    • Table 7. Effect of glyphosate application timing on end-of-season biomass, plant Carmer, S. G., W. E. Nyquist, and W. M. Walker. 1989. Least significant density, and seed production of Florida pusley at Fayetteville, AR, 2002 differences for combined analyses of experiments with two- or three-factor and 2003.a,b treatment designs. Agron. J. 81:665–672. Cavers, P. B. and D. L. Benoit. 1989. Seed banks of arable land. Pages 309–328 Total per meter of row in M. A. Leck, V. T. Parker and R. L. Simpson, eds. Ecology of Seed Banks. San Diego: Harcourt Brace Jovanovich. Timing Biomass Stem number Seed number Chailakhyan, M. K. and V. N. Khrianin. 1978. Effect of growth regulators and role of roots in sex expression in spinach. Planta. 142:207–210. WAE g Clay, P. A. and J. L. Griffin. 2000. Weed seed production and seedling Nontreated 389 a 7a 16,080 a emergence responses to late-season glyphosate applications. Weed Sci. 3 14 b 2b 93 bc 48:481–486. 6 15 b 3b 44 c Coble, H. D. and D. A. Mortensen. 1992. The threshold concept and its 9 162 c 5a 363 b application to weed science. Weed Technol. 6:191–195. Espinoza, L. and J. Ross. 2003. Fertilization and liming. Pages 23–27 in L. a Log-transformed data were used for analysis because of unequal treatment Espinoza and J. Ross, eds. Corn Production Handbook MP437. Little Rock: variances. Log means were separated according to Fisher’s Protected LSD, P 5 Cooperative Extension Service, University of Arkansas. 0.05. Detransformed means are presented with log mean separation. Means Fawcett, R. S. and F. W. Slife. 1978. Effects of 2,4-D and dalapon on weed seed within a column followed by same letter are not significantly different. production and dormancy. Weed Sci. 26:543–547. b Abbreviation: WAE, weeks after emergence. Goughler, J. A. and D. R. Geiger. 1981. Uptake and translocation of N- phosphonomethylglycine in sugarbeet. Plant Physiol. 68:668–672. Haar, M. J. and S. A. Fennimore. 2003. Evaluation of integrated practices for common purslane (Portulaca oleracea) management in lettuce (Lactuca sativa). species by glyphosate can be achieved if applications are made Weed Technol. 17:229–233. early in the season and at high rates. Restricting seed Hamdi, S., G. Teller, and J. P. Louis. 1987. Master regulatory genes, auxin level, production allows producers to manage weed populations and sexual organogenesis in the dioecious plant Mercurialis annua. Plant Physiol. 85:393–399. by limiting seed return to the soil seedbank. Limiting late- Hartzler, R. G. 1996. Velvetleaf (Abutilon theophrasti) population dynamics season seed production will not directly affect crop yields, but following a single year’s seed rain. Weed Technol. 10:581–586. it will improve crop seed purity and will reduce the soil Hopkins, W. G. 1999. Introduction to Plant Physiology. New York: J. Wiley. seedbank over time. The limitations to this procedure include Pp. 215–233. extra input and management, which may decrease the profit Isaacs, M. A., E. C. Murdock, J. E. Taylor, and S. U. Wallace. 1989. Effects of late-season herbicide application on sicklepod (Cassia obtusifolia) seed margin in the short term. However, producers who own their production and viability. Weed Sci. 37:761–765. land or will be farming these fields for years to come may reap Johnson, W. C. and B. G. Mullinix Jr. 2002. Weed management in watermelon the benefits of lower future weed control costs by depleting (Citrullus lanatus) and cantaloupe (Cucumis melo) transplanted on poly- the soil seedbank with late-season glyphosate applications to ethylene-covered seed beds. Weed Technol. 16:860–866. Jones, R. E. and R. W. Medd. 2005. A methodology for evaluating risk and reduce weed seed rain. Future research in this area should efficacy of weed management technologies. Weed Sci. 53:505–514. include the physiological changes caused by glyphosate Jordan, D. L., A. C. York, J. L. Griffin, P. A. Clay, P. R. Vidrine, and D. B. application and the impact of late-season applications on Reynolds. 1997. Influence of application variables on efficacy of glyphosate. herbicide-resistance management. Weed Technol. 11:354–362. Lee, T. T. 1984. Release of lateral buds from apical dominance by glyphosate in soybean and pea seedlings. J. Plant Growth Regul. 3:227–235. Menges, R. M. 1987. Weed seed population dynamics during six years of weed Sources of Materials management systems in crop rotations on irrigated soil. Weed Sci. 1 35:328–332. SAS system for Windows, Version 8, SAS Institute Inc. 100 Norris, R. F. 1985. Weed population dynamics and the concept of zero SAS Campus Drive Cary, NC 27513-2414. thresholds. Weed Sci. Soc. Am. Abstr. 160. Norsworthy, J. K. and L. R. Oliver. 2002a. Hemp sesbania interference in drill- seeded glyphosate-resistant soybean. Weed Sci. 50:34–41. Acknowledgments Norsworthy, J. K. and L. R. Oliver. 2002b. Pitted morningglory interference in drill-seeded glyphosate-resistant soybean. Weed Sci. 50:26–33. The authors would like to express appreciation to the Payne, S. A. and L. R. Oliver. 2000. Weed control programs in drilled Arkansas Soybean Promotion Board for funding this research. glyphosate-resistant soybean. Weed Technol. 14:413–422. Pline, W. A., K. L. Edmisten, J. W. Wilcut, R. Wells, and J. Thomas. 2003. The authors also express appreciation to Dr. Edward Gbur for Glyphosate-induced reductions in pollen viability in glyphosate-resistant advice concerning statistical analysis. cotton and attempted remediation by gibberellic acid (GA3). Weed Sci. 51:19–27. Puricelli, E., D. Faccini, G. Orioli, and M. R. Sabbatini. 2004. Anoda cristata Literature Cited control with glyphosate in narrow- and wide-row soybean. Weed Res. 44:150–156. Abu-Irmaileh, B. E., L. S. Jordan, and J. Kumamoto. 1979. Enhancement of Radosevich, S., J. Holt, and C. Ghersa. 1997. Weed Ecology 2nd ed. New York: CO2 and ethylene production and cellulase activity by glyphosate in Phaseolus J. Wiley. Pp. 130–162. vulgaris. Weed Sci. 27:103–106. Richardson, R. J., H. P. Wilson, G. R. Armiel, and T. E. Hines. 2004. Mixtures Banga, S. S. and K. S. Labana. 1983. Production of F1 hybrids of using ethrel- of glyphosate with CGA 362622 for weed control in glyphosate-resistant induced male sterility in Indian mustard [Brassica juncea (L.) Coss.]. J. Agric. cotton (Gossypium hirsutum). Weed Technol. 18:16–22. Sci. 101:453–455. Sandberg, C. L., W. F. Meggitt, and D. Penner. 1980. Absorption, translocation Barnes, J. W. and L. R. Oliver. 2003. Control practices and glyphosate and metabolism of 14C-glyphosate in several weed species. Weed Res. applications for sicklepod (Senna obtusifolia) control in soybean (Glycine max). 20:195–200. Weed Technol. 17:429–440. Schweizer, E. E. and R. L. Zimdahl. 1984. Weed seed decline in irrigated soil Bennett, A. C. and D. R. Shaw. 2000. Effect of preharvest desiccants on weed after six years if continuous corn (Zea mays) production and herbicides. Weed seed production and viability. Weed Technol. 14:530–538. Sci. 32:76–83. Brewer and Oliver: Reducing weed seed rain with glyphosate N 757
    • Simpson, R. L., M. A. Leck, and V. T. Parker. 1989. Seed banks: general Webster, T. M., J. Cardina, and A. D. White. 2003. Weed seed rain, soil concepts and methodological issues. Pages 3–8 in M. A. Leck, V. T. Parker seedbanks, and seedling recruitment in no-tillage crop rotations. Weed Sci. and R. L. Simpson, eds. Ecology of Seed Banks. San Diego: Harcourt Brace 51:569–575. Jovanovich. Starke, R. J. and L. R. Oliver. 1998. Interaction of glyphosate with chlorimuron, fomesafen, imazethapyr, and sulfentrazone. Weed Sci. 46:652–660. Swahney, V. K. and A. Shukla. 1994. Male sterility in flowering plants: are plant growth substances involved? Am. J. Bot. 81:1640–1647. Received August 25, 2006, and approved March 23, 2007. 758 N Weed Technology 21, July–September 2007