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Production Papers

Time of Weed Removal with Glyphosate Affects Corn Growth and Yield Components

Department of Crop and Soil Sciences, 620 Bradfield Hall, Cornell Univ., Ithaca, NY 14853

^* Corresponding author (wjc3{at}cornell.edu)

Received for publication March 14, 2005.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Growers need to be aware that corn (Zea mays L.) develops leaf area slowly and competes poorly with early emerging weeds in the northeastern USA when planning a total postemergence program in glyphosate-resistant corn. We applied glyphosate at early postemergence (EPOST), third to fourth leaf stage (V3–V4) of corn growth; mid-postemergence (MPOST), V5 to V6 stage; and late postemergence (LPOST), V7 to V8 stage, in New York in 2003 and 2004 to determine how initial glyphosate timing affects growth, development, yield, and yield components of corn. The EPOST treatment, which received glyphosate when weeds were 10 cm or less in height, and a weed-free treatment silked on the same date, had similar dry matter (DM) accumulation (738 g m^–2) and leaf area index (LAI) at silking (3.50), kernels per plant (528–549), and grain yield (11.1 Mg ha^–1). The MPOST treatment, which received glyphosate when some weeds were 18 to 35 cm tall, silked 2 d later, had 35% less LAI and 39% less DM accumulation at silking, 21% less kernels per plant, and 25% less grain yield. Although the LPOST and untreated control, which had 1363 and 653 weeds m^–2 at the V5–V6 stage in 2003 and 2004, respectively, had the same LAI at silking (1.75–1.87), the LPOST treatment yielded higher (6.4 vs. 3.2 Mg ha^–1). Results from this study indicate that growers in the northeastern USA should apply glyphosate by the V3–V4 stage to avoid yield losses from early season weed competition.

Abbreviations: DM, dry matter • EPOST, early postemergence • LAI, leaf area index • LPOST, late postemergence • MPOST, mid-postemergence • R1, silking stage • Vn, nth leaf stage

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
CORN develops leaf area and accumulates DM slowly under the cool spring conditions in the northeastern USA (Cox et al., 1990). Consequently, corn competes poorly with early emerging weeds in New York (Mohler et al., 1997). Corn growers who plant glyphosate-resistant corn in the northeastern USA need to know when a total postemergence glyphosate weed control program must be initiated to prevent yield loss from early season weed competition.

Hall et al. (1992) reported that the critical period of weed control in corn occurred from the third to 14th leaf stage. This indicates that corn tolerated early season weed competition without yield loss only until the third leaf stage in the cool spring conditions of Ontario, Canada. The results from the Canadian study suggest that glyphosate may have to be applied as early as the V3 stage (Ritchie et al., 1993) to prevent yield losses from early season weed competition in regions with cool spring conditions. Gower et al. (2003) reported that the optimum timing for weed control and corn yields for an initial application of glyphosate generally occurred by the V4 stage in the north-central USA when weeds were less than 10 cm in height. Dalley et al. (2004), however, reported that the optimum timing for weed control and corn yields depended on specific annual growing conditions in Michigan. In highly competitive conditions (high weed densities and below normal precipitation), optimum glyphosate application for weed control and corn yield occurred by the V4 stage. In less competitive conditions, optimum glyphosate application for weed control and corn yield occurred as late as the V9 stage. Gower et al. (2002) reported that glyphosate should be applied before weeds attain 15 cm in height to avoid yield losses in Ohio. They concluded that reinfestation of weeds after an EPOST application had less potential to reduce yield than delaying application and allowing weeds to compete with corn for too long a period before removal.

Kernel number is the yield component that most influences grain yield of corn (Tollenaar, 1977; Otegui, 1997; Andrade et al., 1999). Maddonni and Otegui, (2004) suggested that the physiological state of the corn plant resulting from interplant competition between corn plants may determine kernel number of corn as early as the V7 stage. Most weed control studies have not estimated kernel number in corn. Only one study (Evans et al., 2003b) reported that early season weed competition reduced kernel number. The objective of this study was to evaluate how early season weed competition in relation to the timing of an initial glyphosate application affects growth, development, yield, and yield components, especially kernel number development, of corn under the cool growing conditions in the northeastern USA.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Field experiments were conducted in 2003 and 2004 on a Honeoye silt loam soil (fine-loamy, mixed, mesic Glossoboric Hapludalf) at a Cornell University research farm near Aurora, NY (42°44' N, 76°40' W). The experimental sites, which were adjacent to each other, were fallowed in the previous year to the experiment. In the fallow year, the experimental site was moldboard plowed in the spring and then left fallow for the remainder of the year. In the experimental year, the sites received an application of 0.84 kg acid equivalent (a.e.) ha^–1 of glyphosate [N-(phosphonomethyl)glycine] and 0.56 kg a.e. ha^–1 of 2,4-D [(2,4-dichlorophenoxy) acetic acid] ester in late April for control of perennial weeds, primarily dandelion (Taraxacum officinale Weber in Wiggers). The experimental sites were then disked and harrow-cultipacked before planting. Soil tests of the experimental sites indicated a pH of 7.9 in 2003 and 7.8 in 2004 with medium concentrations of P and K (Mehlich Test) in both years.

DeKalb brand ‘DKC42-70RR’, 92-d Relative Maturity (RM), and ‘DKC53-33RR’, 103-d RM, were planted on 5 May 2003 and 11 May 2004 with a four-row planter at 0.76 m row spacing and 88000 kernels ha^–1 with 225 kg ha^–1 of the starter fertilizer, 10–20–20. All plots received about 110 kg N ha^–1 as a 32% (w/v) N solution of urea [(NH₂) Co] and ammonium nitrate (NH₄NO₃) at the V5 stage of corn growth in both years.

Weed control treatments included an untreated control, a weed-free plot, and three postemergence glyphosate treatments. The weed-free plot received a mixture of 1.12 kg a.i. ha^–1 of atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-24-diamine]) and 1.4 kg a.i. ha^–1 of S-metolachlor [2-chloro-N-(2-ethyl-6- methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] applied pre-emergence followed by a glyphosate application at LPOST. Glyphosate treatments were 1.14 kg a.i. ha^–1 (applied as 1.9 L of Roundup ULTRA MAX ha^–1) at EPOST, the V3–V4 stage of corn growth; MPOST, the V5–V6 stage; and LPOST, the V7–V8 stage (Table 1). The EPOST and MPOST treatments also received a second glyphosate application at LPOST. All herbicides were applied with a tractor-mounted compressed-air sprayer with flatfan nozzles (80015) at 50 cm spacing. The sprayer was calibrated to deliver 187 L ha^–1 at 235 kpa pressure at a ground speed of 3.2 km h^–1. Boom height was 51 cm above the soil surface for the preemergence application, 56 cm for the EPOST, 71 cm for the MPOST, and 91 cm for the LPOST herbicide applications.

Weed population densities, by species, were counted within a 0.23 m² quadrant in the two outer sampling areas in the untreated control at the V5 stage in 2003 and V6 stage in 2004 (Table 1). Five corn plants were selected at the V8 growth stage (3 July in 2003 and 1 July in 2004) and the R1 growth stage (28 and 31 July in 2003 and 23 and 27 July in 2004). Green leaves were measured with an LI-3100 leaf area meter (LI-COR, Lincoln, NE) and then placed with the remaining plant parts in a forced-air dryer and dried at 60°C to constant moisture. Total DM accumulation and LAI values were calculated on a land area basis determined by final plant densities in each subplot (average of 81 375 plants ha^–1 in 2003 and 81 350 in 2004).

Ten plants from the center two rows were randomly selected to determine yield and yield components of corn. The number of rows per ear and kernels per row were counted before drying at 60°C to constant moisture in a forced-air drier. The ears were then hand-shelled and the number of kernels was counted with a seed counter (Old Mill Co., Savage, MD). The total number of kernels was then weighed to determine kernel weight. Grain yield was calculated from the weight of the total number of kernels on a land area basis determined by final plant densities in each subplot.

Daily precipitation and maximum and minimum temperatures (1.5 m) were recorded daily at a weather station at the research farm. We calculated growing degree days (GDD), based on the 30 to 10°C system. We also calculated thermal time, based on daily mean temperatures above 8°C from the day after planting, to present thermal units (°Cd) at the time of glyphosate application (Otegui, 1997).

We conducted separate statistical analyses for each year and a combined analysis across years. The Bartlett test indicated homogeneous variance for all measured variables across years so we will present the combined analysis across years. We used the Shapiro-Wilk statistic in the PROC CAPABILITY: NORMAL TEST option of the SAS statistical package, version 7.0 software (SAS Institute, 1998) to test for normalcy. All of the combined data tested normal so transformation of the data was not necessary. Hybrids and weed control treatments were considered fixed, and replications and years were considered random in the analysis of variance. Hybrid x weed control interactions were not observed for any measured variables so the results were averaged across hybrids. We used the General Linear Model (GLM) procedures of the SAS statistical package, version 7.0 software (SAS Institute, 1998). All effects were considered significant at = 0.05. Fisher's protected LSD ( = 0.05) was used to separate means when main effects tested significant.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The 2003 and 2004 growing seasons were mostly stress-free for corn growth, development, and yield. May through July was cool and wet but August was warm and dry in 2003 (Table 2). Visual observations indicated incipient drought stress in the untreated control in late August, 30 to 35 d after silking, but a 36 mm precipitation event on 1 September relieved the crop from further stress. May, July, and August were exceptionally wet, and June, July, and August were cool in 2004 (Table 2). June and early July were cool and dry but a 26 mm precipitation event on 7 July, 15 to 20 d before silking, prevented drought stress from developing. The weed-free treatment provided similar yield under the stress-free conditions in 2003 (11.1 Mg ha^–1) and 2004 (11.0 Mg ha^–1).

Weed population density in 2004 totaled 653 weeds m^–2 in the untreated control at the V6 stage, with most weeds emerging with corn or a few days thereafter (Table 1). Population densities of common ragweed (Ambrosia artemisiifolia L.) totaled 211 m^–2, green foxtail totaled 155 m^–2, and common lambsquarters totaled 108 m^–2. In addition, the population density of yellow nutsedge (Cyperus esculentus L.), which measured 18 cm in height at the V6 stage, totaled 70 m^–2. Thomas et al. (2004) reported that yellow nutsedge population densities of 50 m^–2, which measured 15 to 20 cm in height at the V5 to V6 stage, reduced corn yields by 85% in North Carolina. Although weed population densities were more than 50% less in 2004 vs. 2003, the untreated control yielded similarly in 2003 (3.0 Mg ha^–1) and 2004 (3.4 Mg ha^–1). Visual estimates at the R1 stage indicated greater than 95% weed control in the three postemergence glyphosate treatments and 100% control in the weed-free treatment (data not shown).

Corn given the weed-free and EPOST treatments silked on the same date (Table 3). A delay in glyphosate application until MPOST resulted in a 2-d delay in silking, and a further delay in glyphosate application until LPOST resulted in a 3-d delay in silking. A 2- to 3-d delay in silking can negatively impact corn in northern latitudes because it increases the risk of a fall frost before corn attains physiological maturity. The untreated control silked 5-d later vs. the weed-free treatment, which is consistent with the 4-d delay reported by Evans et al. (2003a) in a Nebraska study.

The LPOST treatment had a 61% reduction in LAI and a 65% reduction in DM accumulation at the V8 stage and a 47% reduction in LAI and a 55% reduction in DM accumulation at the R1 stage when compared with the weed-free treatment. The 47% reduction in LAI greatly exceeded the 24% reduction in maximum LAI in a LPOST treatment (glyphosate application at the V9 stage) in a Nebraska study in which weed population densities ranged from 80 to 364 weeds m^–2 (Evans et al., 2003a). In fact, the LPOST and untreated control had the same LAI at the R1 stage in our study, whereas the untreated control had only a 33% reduction in maximum LAI in the Nebraska study and a 4 to 35% reduction in maximum LAI in a Canadian study (Cathcart and Swanton, 2004). Apparently, higher weed population densities and perhaps taller weeds in our study compared with the Nebraska and Canadian studies resulted in greater reductions in vegetative growth in the LPOST and untreated control, despite no water stress during vegetative development.

The weed-free and EPOST treatments yielded the same, whereas the MPOST treatment yielded 25% less (Table 4). Significant weed competition before the V3 to V4 stage did not influence growth, development, and yield, but significant weed competition up to the V5 to V6 stage delayed silking by 2-d, reduced DM accumulation at silking by 39%, and reduced grain yield by 25%. The critical weed control period under the environmental conditions of this study began shortly after the V3 to V4 stage. This finding agrees with the findings of Hall et al. (1992) in their pioneering study in Ontario, Canada, which has environmental conditions similar to those in the northeastern USA.

The LPOST treatment yielded 42% less and the untreated control yielded 71% less when compared with the weed-free treatment. Although the LPOST and untreated control had similar LAIs and DM accumulation at the R1 stage, the untreated control yielded 50% less than the LPOST treatment. Obviously, the critical weed-free period extended far beyond the V7 to V8 stage in this study. The relationships between LAI and DM accumulation at the R1 stage and grain yield were curvilinear rather than linear in this study (data not shown), which agrees with the findings of Evans et al. (2003a).

Weed control treatments did not affect ear number per plant (Table 4). Evans et al. (2003b) also reported that ear number had minimal effect on yield losses associated with weed interference in a weed control timing study. In a corn silage study in New York, (Cox et al., 2005), however, the untreated control produced no ears in a year when only 20 mm of precipitation occurred from the V8 to R1 stage. In 2003 and 2004, the wet and cool conditions from the V8 to R1 stage (1–28 July) allowed for ear development, despite 653 to 1363 weeds m^–2 in the untreated control at the V5–V6 stage, the beginning of ear development (Ritchie et al., 1993).

The EPOST and weed-free treatments averaged similar numbers of rows per ear, kernels per row, and kernels per plant (Table 4). The MPOST treatment averaged 0.8 less rows per ear, 6.2 less kernels per row, and 118 less kernels per plant vs. the weed-free treatment. In 2003, the MPOST application occurred at 302°Cd, well before the thermal time (350–450°Cd) reported for the beginning of row organization in corn (Otegui and Melon, 1997; Otegui, 1997). Nevertheless, the MPOST averaged 15.4 rows per ear vs. 16.1 in the weed-free treatment in 2003. It is not clear if weed interference at the V5–V6 stage in both years had a direct effect on row number or if the smaller plant at R1 stage resulted in less biomass allocation to developing kernels, resulting in kernel abortion of an entire row of corn (Otegui, 1997). Also, there is a lag between glyphosate application and weed death, which could have extended the impact of weed interference of tall weeds via shading in the MPOST treatment until the V7 stage, the beginning of the critical period of kernel number determination of maize (Maddonni and Otegui, 2004). Regardless of the mechanism, a delay in glyphosate application from the V3–V4 to V5–V6 stage resulted in almost 100 less kernels per plant, the yield component that correlates most closely with yield (Tollenaar, 1977; Andrade et al., 1999).

The LPOST treatment averaged 1.8 less rows per ear, 9.1 less kernels per row and 188 less kernels per plant when compared with the weed-free treatment. Despite similar LAI values and DM accumulation at the R1 stage, the LPOST treatment averaged 9.6 more kernels per row and 147 more kernels per plant when compared with the untreated control. Apparently, weed interference during the 3 wk period after silking contributed to kernel abortion in the untreated control. Even in 2004, when maximum temperatures averaged only 24°C and precipitation totaled 89 mm during the 3-wk period after silking, the untreated control averaged 10 less kernels per row and 160 less kernels per plant compared with the LPOST treatment. Weed interference in the untreated control from the V8 to R1 stage, when potential kernel number is determined (Maddonni and Otegui, 2004), probably also contributed to less kernels per plant when compared with the LPOST treatment.

The untreated control averaged less kernel weight when compared with the EPOST and MPOST treatments, but averaged similar kernel weight when compared with the weed-free and LPOST treatments (Table 4). Kernel weight was much less sensitive to weed interference than kernel number, findings that agrees with the findings of Evans et al. (2003b). A reduction in postsilking crop growth rates from 2 to 6-wk after silking reduces kernel weight in corn (Maddonni et al., 1998), which Cathcart and Swanton (2004) attributed to an 8 to 12% reduction in kernel weight when green foxtail population densities exceeded 50 m^–2. All treatments except for the untreated control had mostly weed-free conditions during the grain-filling period, which probably contributed to their similar kernel weights.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The critical period for weed control began shortly after the V3–V4 stage of corn growth when all weed species, which totaled 1363 m^–2 in the untreated control at the V5 stage in 2003 and 653 m^–2 at the V6 stage in 2004, were 10 cm or less in height. A delay in glyphosate application until the V5–V6 stage, when wild mustard (134 m^–2) measured 35 cm in height in 2003 and yellow nutsedge (70 m^–2) measured 18 cm in height in 2004, delayed silking by 2 d, reduced LAI at silking by 35% and DM accumulation by 39%, kernel number by 21%, and grain yield by 25%. Rajcan and Swanton (2001) postulated that early season weed interference alters light quality (far red/red) and triggers shade avoidance characteristics in corn, resulting in reduced photosynthetic rates and reduced water and nutrient absorption. Also, Maddonni and Otegui (2004) reported that interplant competition among corn plants began at the V4 to V6 stage, which affected subsequent crop growth, kernel number, and grain yield. The delay in glyphosate application from the V3 to V4 stage until the V5 to V6 stage resulted in 0.7 less rows per ear, which indicates that weed interference between the V4 to V6 stage may have directly affected reproductive development in corn. The results from this study indicate that growers should apply glyphosate by the V3 to V4 stage to avoid yield losses from early season weed competition in the cool spring conditions in the northeastern USA.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Andrade, F.H., C. Vega, S. Uhart, A. Cirilo, M. Cantarero, and O. Valentinuz. 1999. Kernel number determination in miaze. Crop Sci. 39:453–459.[Abstract/Free Full Text]
• Cathcart, R.J., and C.L. Swanton. 2004. Nitrogen and green foxtail (Setaria viridis) competition effects on corn growth and development. Weed Sci. 52:1039–1049.
• Cox, W.J., R.W. Zobel, H.M. van Es, and D.J. Otis. 1990. Growth, development and yield of maize under three tillage systems in the northeastern USA. Soil Tillage Res. 18:295–310.[CrossRef]
• Dalley, C.D., J. Kells, and K. Renner. 2004. Effect of glyphosate application timing and row spacing on corn (Zea mays) and soybean (Glycine max) yields. Weed Technol. 18:165–176.
• Evans, S., S. Knezevic, J. Lindquist, and C. Shapiro. 2003a. Influence of nitrogen and duration of weed interference on corn growth and development. Weed Sci. 51:546–556.
• Evans, S., S. Knezevic, J. Lindquist, C. Shapiro, and E.E. Blankership. 2003b. Nitrogen application influences the critical period for weed control in corn. Weed Sci. 51:408–417.
• Gower, S.A., M. Loux, J. Cardina, and S.K. Harrison. 2002. Effect of planting date, residual herbicide, and postemergence application timing on weed control and grain yield in glyphosate-tolerant corn (Zea mays). Weed Technol. 16:488–494.[CrossRef]
• Gower, S.A., M. Loux, J. Cardina, S.K. Harrison, P.L. Sprankle, N.J. Probst, T.T. Bauman, W. Bugg, W.S. Curran, R.S. Currie, R. Gordon Harvey, W.G. Johnson, J.J. Kells, M.D. Owen, D.L. Regehr, C.H. Slack, M. Spaur, C.L. Sprague, M. Vangessel, and B.G. Young. 2003. Effect of postemergence glyphosate application timing on weed control and grain yield in glyphosate-resistant corn: Results of a 2-year multistate study. Weed Technol. 17:821–828.
• Hall, M.R., C.L. Swanton, and G.W. Anderson. 1992. The critical period of weed control in grain corn (Zea mays). Weed Sci. 40:441–447.
• Maddonni, G.A., and M.E. Otegui. 2004. Intra-specific competition in maize: Early establishment of hierarchies among plants affects final kernel set. Field Crops Res. 85:1–13.[CrossRef]
• Maddonni, G.A., M.E. Otegui, and R. Bonhommie. 1998. Grain yield components in maize: II. Postsilking growth and kernel weight. Field Crops Res. 56:257–264.[CrossRef]
• Mohler, C.L., J.C. Frisch, and J. Mt. Pleasant. 1997. Evaluation of mechanical weed management programs for corn (Zea mays L.). Weed Technol. 11:123–131.
• Otegui, M.E. 1997. Kernel set and flower synchrony within the ear of maize: II. Plant population effects. Crop Sci. 37:448–455.[Abstract/Free Full Text]
• Otegui, M.E., and S. Melon. 1997. Kernel set and flower synchrony within the ear of maize: I. Sowing date effects. Crop Sci. 37:441–447.[Abstract/Free Full Text]
• Rajcan, I., and C.J. Swanton. 2001. Understanding maize-weed competition: Resource competition, light quality, and the whole plant. Field Crops Res. 71:139–150.
• Ritchie, S.W., J.J. Hanway, and G.O. Benson. 1993. How a corn plant develops. Coop. Ext. Serv. Spec. Rep. Iowa State Univ., Ames. IA. 48.
• SAS Institute. 1998. SAS user's guide: Statistics Version 7 Fourth ed. SAS Inst., Cary, NC.
• Sikkema, P.H., C. Shropshire, A.S. Weaver, and P.B. Cavers. 2004. Response of common lambsquarters (Chenopodium album) to glyphosate application timing and rate in glyphosate-resistant corn. Weed Technol. 18:908–916.
• Tharp, B.E., and J.J. Kells. 1999. Influence of herbicide application rate, timing and interrow cultivation on weed control and corn (Zea mays) yield in glufosinate-resistant and glyphosate-resistant corn. Weed Technol. 13:807–813.
• Thomas, W.E., I.C. Burke, and J.W. Wilcut. 2004. Weed management in glyphosate-resistant corn with glyphosate, halosulfuron, and mesotrione. Weed Technol. 18:826–834.
• Tollenaar, M. 1977. Sink-source relationships during reproductive development in maize. A review. Maydica 22:49–75.

This Article Abstract Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Cox, W. J. Articles by Stachowski, P. J. Search for Related Content PubMed Articles by Cox, W. J. Articles by Stachowski, P. J. Agricola Articles by Cox, W. J. Articles by Stachowski, P. J. Related Collections Weed Management Maize Production Agriculture