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INTEGRATED PEST MANAGEMENT

Agronomics and Economics of Different Weed Management Systems in Corn and Soybean

^a Dep. of Plant Pathology, Cornell Univ., Ithaca, NY 14853 USA
^b Dep. of Ext., Rutgers Univ., New Brunswick, NJ 08901-8520 USA

wjc3{at}cornell.edu

Received for publication July 9, 1998.

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and methods NOTES Results and discussion Conclusion REFERENCES

 
The USDA has a goal of implementing integrated pest management (IPM) practices on 75% of crop area by 2000. Growers require more economic information before adopting IPM practices. A field study was initiated in New York to evaluate weed control, yields, and net returns of chemical (broadcast herbicides), chemical–mechanical (banded herbicides and cultivations), and mechanical (rotary hoe and cultivations) weed management under moldboard plow and chisel tillage in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. Chemical and chemical–mechanical weed management had similar corn net returns under moldboard plow ($370 and $355 ha^-1, respectively) and chisel tillage ($282 and $287 ha^-1). Mechanical weed management had less net returns in moldboard plow ($302 ha^-1) and chisel tillage ($121 ha^-1) because of 15% lesser corn densities and greater weed densities, especially in chisel tillage. In soybean, mechanical weed management in moldboard plow tillage had similar weed density (1.5 weeds m^-2) lower yield (2.71 Mg ha^-1), but similar net return ($107.50 ha^-1) compared with chemical (1.3 weeds m^-2, 2.92 Mg ha^-1, and $85.60 ha^-1, respectively) and chemical–mechanical weed management (1.0 weeds m^-2, 2.78 Mg ha^-1 and $99.35 ha^-1, respectively). In chisel tillage, mechanical weed management had greater weed density (7.4 weeds m^-2), lower yield (2.2 Mg ha^-1), and lower net return (-$7.80 ha^-1) compared with chemical (1.9 weeds m^-2, 2.8 Mg ha^-1, and $56.80 ha^-1, respectively) and chemical–mechanical weed management (1.9 weeds m^-2, 2.4 Mg ha^-1, and $27.30 ha^-1). Corn and soybean growers apparently can adopt chemical–mechanical weed management and maintain net returns. Soybean growers who use moldboard plow tillage can also adopt mechanical weed management and maintain net returns.

Abbreviations: GDD, growing degree days • IPM, integrated pest management

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and methods NOTES Results and discussion Conclusion REFERENCES

 
THE USDA and USEPA have a goal of implementing IPM practices on 75% of the crop area by the year 2000 (USDA, 1993). Some IPM practices in weed management that reduce and/or eliminate herbicide use include using banded herbicides and/or the rotary hoe supplemented by timely cultivations. Growers require more information, especially economic information, before they will adopt these weed management practices.

Several studies during the last 10 yr have examined weed management systems in corn that use banded herbicides and/or the rotary hoe supplemented by cultivation (Mulder and Doll, 1993; Hartzler et al., 1993; Mt. Pleasant et al., 1994; Buhler et al., 1995; VanGessel et al., 1995; Krausz et al., 1995; Mohler et al., 1997). The use of banded herbicides supplemented by cultivation resulted in similar or greater weed control and corn yields compared with broadcast herbicides (Mulder and Doll, 1993; Hartzler et al., 1993; Mt. Pleasant et al., 1994; Krausz et al., 1995). The use of the rotary hoe supplemented by cultivation compared with broadcast herbicides resulted in similar or lower weed control and corn yields (Buhler et al., 1995; VanGessel et al., 1995; Mohler et al., 1997). Environmental conditions during the first week after the rotary hoe operation strongly influence weed control and subsequent corn yields (Lovely et al., 1958).

Relatively few studies during the last 10 yr have examined the use of banded herbicides and/or the rotary hoe supplemented by cultivation in soybean (Buhler et al., 1992; Krausz et al., 1995; Buhler and Gunsolus, 1996). The use of banded herbicides supplemented by cultivation resulted in similar or greater weed control and soybean yields compared with broadcast herbicides (Buhler et al., 1992; Krausz et al., 1995). As with corn, the effectiveness of the rotary hoe for weed control in soybean varied with environmental conditions. The use of the rotary hoe supplemented by cultivation compared with broadcast herbicides resulted in similar weed control and soybean yield in a year with dry spring conditions, but lower weed control and yield in a year with wet spring conditions (Buhler et al., 1992). Also, the use of the rotary hoe supplemented by cultivation compared with broadcast herbicides resulted in similar weed control and soybean yield for an early-June planting date, but less weed control and yield for a mid-May planting date in Minnesota (Buhler and Gunsolus, 1996).

Most researchers have conducted weed control studies under one tillage system. Also, most researchers have not included an economic analysis of weed management systems, despite the importance of economics in influencing grower adoption of management practices. Our objective was to evaluate weed control, yield, and net returns of three weed management systems under two tillage systems in corn and soybean.

	Materials and methods

TOP ABSTRACT INTRODUCTION Materials and methods NOTES Results and discussion Conclusion REFERENCES

 
A 4-yr field study was initiated in 1993 on a shallow Honeoye silt loam soil (fine-loamy, mixed, mesic Glossoboric Hapludalf) at a Cornell University Research Farm near Aurora, NY (42°26' N, 76°26' W). Soil tests indicated a pH of about 7.5 and high soil test values of P and K in the early spring of each growing season. Winter wheat (Triticum aestivum L.) was planted at the site in 1992. Chisel tillage was the primary tillage operation at the site from 1988.

Two tillage systems (moldboard plow and chisel tillage), two crop rotations (continuous corn and soybean–corn), and three weed management systems (chemical, chemical–mechanical, and mechanical) were evaluated in a randomized complete block design in a split-split plot arrangement with three replications. Main plots, 100 m long by 27 m wide, consisted of tillage systems. Moldboard plow and chisel tillage operations were performed each spring. Subplots, 100 m long by 9 m wide, consisted of crop rotations. The soybean–corn rotation was in both phases in all years, so soybean following corn, corn following soybean, and continuous corn were planted each year. Sub-subplots, 100 m long by 3.3 m wide, consisted of weed management systems.

Weed management systems evaluated in corn included: (i) chemical, (ii) chemical–mechanical, and (iii) mechanical. The chemical weed management system in corn received a broadcast preemergence application (1 to 2 d after planting) of 2.5 kg ha^-1 a.i. of cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile} and 2.2 kg ha^-1 a.i. of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], followed by a spot-spray postemergence application of 0.56 kg ha^-1 a.i. of dicamba (3,6-dichloro-2-methoxybenzoic acid). About one-third of the plot area in chemical weed management received dicamba in each year of the study to control annual weed escapes and/or perennial weeds not controlled by the preemergence herbicides. The chemical–mechanical weed management system received the same rate of the preemergence application of cyanazine and metolachlor in a band at planting, followed by cultivations at the three-leaf stage (V3; Ritchie et al., 1993) and V6 stage. The mechanical weed management system in corn received two rotary hoe operations, just before emergence and a few days after emergence, followed by cultivations at the V3 and V6 stages. A Danish S-tine cultivator (Dakon, Tebben Mfg. Co., Clara City, MN¹) was used for all cultivations. A John Deere Model 400 rotary hoe (John Deere, Moline, IL) was used for all rotary hoe operations.

Weed management systems evaluated in soybean were likewise chemical, chemical–mechanical, and mechanical systems. The chemical weed management system received a broadcast preemergence application of 2.2 kg ha^-1 a.i. of linuron [N'-(3,4-dichlorophenyl)-N-methoxy-N-methylurea] and 2.2 kg ha a.i. of metolachlor. The chemical–mechanical weed management system received the same rate of the preemergence application of linuron and metolachlor, followed by cultivations at the V2 stage (Ritchie et al., 1992) and at about the V5 stage. The mechanical weed management system in soybean received one rotary hoe operation just before emergence in 1994 and 1995, followed by cultivations at the V2 and V5 stages. In 1996, mechanical weed management received two rotary hoe operations, just before and after emergence, followed by two cultivations. The mechanical weed management system received a second rotary hoe operation in 1996, because wet soil conditions resulted in continued emergence of annual weeds.

Pioneer `3733' hybrid corn (99 d relative maturity) was planted at 0.76-m row spacing at a planting rate of 72000 kernels ha^-1 with a White Air Seeder (Coldwater, OH) during the last week of April in all years, except in 1996, when planting was delayed until 17 May because of wet soil conditions. Corn received a starter fertilizer of 28, 56, and 56 kg ha^-1 of N, P, and K at planting. At the V4 stage, corn also received 135 kg N ha^-1 as a 32% N solution of urea and NH₄NO₃, injected about 0.1 m deep between rows. At planting, continuous corn also received 1.12 kg ha^-1 a.i. of terbufos {S-[[(1,1-dimethylethyl)thio]methyl] O,O-diethyl phosphorodithioate}, a soil insecticide used for control of corn rootworm (Diabrotica spp.).

Pioneer `9162', a mid-Maturity Group I soybean variety, was planted on 12 or 13 May in each year of the study, except in 1996, when corn and soybean were planted on the same date, 17 May. Soybean in the chemical weed management system was planted with the White Air Seeder in 0.38-m row spacing at a planting rate of 494000 seeds ha^-1. Soybean in the chemical–mechanical and mechanical weed management systems was also planted at 494000 seeds ha^-1 with the White Air Seeder, but at 0.76-m row spacing, to allow for cultivation. Soybean is usually solid-seeded in New York, so we planted soybean in the chemical weed management system at 0.38-m row spacing.

Corn densities were determined at approximately the V4 stage by counting the number of plants along the entire length of the two center harvest rows in each sub-subplot. Also, weed densities in corn were determined at about the V8 growth stage by counting all the weeds (>5 mm in height) in a 1.5-m width straddling the entire length of the two center harvest rows. Weeds that were <5 mm high were not counted, because we did not believe that they would interfere with the growth and yield of corn.

Soybean densities were determined at approximately the V2 stage by counting the number of soybean plants in eight 1-m lengths in randomly selected areas of each sub-subplot. Also, weed densities in soybean were determined at about the V7 stage by counting all the weeds (>5 mm in height) in a 1.5-m width straddling the entire length of the two center harvest rows in chemical–mechanical and mechanical weed management systems. In the chemical weed management system, planted at 0.38-m row spacing, weed densities were determined by counting all the weeds in a 1.14-m width straddling the entire length of the three center harvest rows.

Soybean was harvested in early October of each year at about 130 g kg^-1 moisture content with a two-row plot combine, fitted with a small-grain head. The two center rows were harvested in the chemical–mechanical and mechanical weed management systems and the three center rows were harvested in the chemical weed management system. Soybean samples were collected for each treatment to determine seed moisture. Corn was harvested in late October or early November of each year at about 220 g kg^-1 moisture content with a two-row plot combine, fitted with a two-row corn head. Corn samples were collected for each treatment to determine grain moisture. Soybean yields were adjusted to 130 g kg^-1 moisture content and corn yields were adjusted to 155 g kg^-1.

Production costs were calculated for both corn and soybean under different tillage and weed management systems using average costs for 1994 to 1996. Seed, fertilizer, and pesticide costs were determined by multiplying the average variable inputs over the 3-yr period by the average 3-yr prices, which were obtained from local agribusinesses. Machinery operation costs as well as drying and hauling costs were determined using custom rates (Pennsylvania Agric. Stat., 1996). Custom rates include ownership, operation labor, fuel, and repair and maintenance costs normally associated with machine operation. Interest on operating capital was calculated using the average commercial interest rate (8.53%) over the 3-yr period as reported by Farm Credit (Hastings, 1996). Crop insurance and land rental charges were determined using actual farmer insurance costs ($30 ha^-1 for corn and $20 ha^-1 for soybean) and typical land rental fees ($148 ha^-1 in central New York.

The marketing year weighted averages in New York from 1994 to 1996 were $0.1269 kg^-1 for corn and $0.214 kg^-1 for soybean (New York Agric. Stat. 1997). Gross returns for both crops were determined as the product of the average crop price and the average yield across the 3 yr. Net returns were calculated as the difference between gross returns and productions costs.

All data were analyzed with analysis of variance (ANOVA) procedures using the SAS statistical software package (SAS Inst., 1991). Different seed treatments were used within weed management systems in both crops in 1993, so we will not present that data to avoid potential confounding effects. A combined analysis of the 1994 to 1996 data indicated year x tillage x weed management interactions for weed densities and yield, so separate analyses were also conducted for each year. Tillage x rotation interactions were not observed for any corn data, so the corn data have been averaged across rotations. Means separation among weed management means and between tillage means were obtained by Fisher's least significant difference (LSD). Effects were considered significant in all statistical calculations for P-values 0.05.

	Results and discussion

TOP ABSTRACT INTRODUCTION Materials and methods NOTES Results and discussion Conclusion REFERENCES

 
Weather Conditions
Weather conditions differed markedly among the three growing seasons (Table 1) . The 1994 growing season had above-normal growing degree days (GDD) with close to normal precipitation during vegetative development (May, June, and July), and below-normal GDD and above-normal precipitation during grain filling (August and the first half of September). The 1995 growing season had above-normal GDD and below-normal precipitation during vegetative development (May, June, and the first half of July) and above-normal GDD and precipitation during grain filling (mid-July through August). The 1996 growing season had below-normal GDD and above-normal precipitation during vegetative development (May, June, and July) and above-normal GDD and normal precipitation during grain filling (August and the first half of September). Corn had visible leaf wilting, associated with dry conditions, almost daily from mid-June until mid-July in 1995. In 1996, corn had some leaf yellowing in early June, associated with excessively wet conditions, and incipient leaf wilting in late August and early September associated with dry conditions.

Tillage and weed management systems affected corn yield, but there was a significant year x tillage x weed management interaction (Table 4) . In 1994, corn yielded the same in chemical–mechanical and chemical weed management in chisel tillage. In contrast, corn yielded 9% less in chemical–mechanical than in chemical weed management in moldboard plow tillage. Hartzler et al. (1993) reported that corn yielded the same with banded herbicides supplemented by cultivation as with broadcast herbicides in almost all on-farm studies in Iowa. Likewise, Mt. Pleasant et al. (1994) reported no yield difference between the two weed management systems under moldboard plow tillage in New York. Weed and corn densities did not differ between chemical–mechanical and chemical weed management in moldboard plow tillage in 1994, so it is not clear why there was a 9% yield difference.

In the dry 1995 growing season, corn yielded the same in mechanical and chemical weed management under moldboard plow tillage, which is as expected, because weed densities did not differ between the two weed management systems. In contrast, corn yielded 26% less in mechanical compared with chemical weed management under chisel tillage, probably because of greater weed density and 11% lesser corn density. Corn yielded the same in chemical–mechanical and chemical weed management systems under both tillage systems in 1995, which is consistent with other studies (Mulder and Doll, 1993; Mt. Pleasant et al., 1994; Hartzler et al., 1993).

In 1996, weed management affected corn yield, but there was no tillage x weed management interaction. Averaged across tillage systems, corn yielded 18% less in mechanical than in chemical weed management, because of much greater weed density and 16% lesser corn density. Averaged across tillage systems, corn yielded 6% less in chemical–mechanical than in chemical weed management. Weed densities and corn densities did not differ between the two weed management systems, so it is not clear why there was a 6% yield difference. Averaged across years, moldboard plow compared with chisel tillage had greater yields, probably because of greater corn densities and lesser weed densities.

Weed management systems, however, must be justified on the basis of economic returns as well, rather than on weed control and crop yield alone (VanGessel et al., 1995). Weed management costs averaged $112.40 ha^-1 for chemical, $66.20 ha^-1 for chemical–mechanical, and $61.25 ha^-1 for mechanical weed management (Table 5) . Krausz et al. (1995) reported that weed management costs did not vary greatly among different weed management systems in corn. However, they did not include spray application costs, which we included for both preemergence and postemergence applications ($34.60 ha^-1) in chemical weed management.

Soybean
Weed densities had a significant tillage x weed management interaction in each year of the study (Table 6) . Weed management treatments in moldboard plow tillage did not affect weed densities in any year of the study. Buhler et al. (1992) reported that mechanical weed management in moldboard plow tillage provided the same weed control as chemical weed management in the first year, but resulted in greater densities of common lambsquarters in the second year. Mechanical weed management controlled common lambsquarters (a dominant weed species in moldboard plow tillage) as well as chemical weed management did in all 3 yr of our study. Gunsolus (1990) suggested that mechanical weed management is less of a challenge in soybean than in corn, because the later soybean planting date allows for secondary tillage operations that eliminate many early-season weeds before planting. In 1996, however, corn and soybean were planted on the same date (17 May) and had rotary hoe operations on the same dates (22 and 30 May). Nevertheless, soybean had only 1.7 weeds m^-2, whereas corn had 3.8 weeds m^-2 in mechanical weed management under moldboard plow tillage. Soybean density, which averaged 33 plants per meter of row in 1996, compared with 5 corn plants per meter of row (data not shown), apparently resulted in more competitiveness against weeds in the row.

Averaged across years, soybean yield had a significant year x tillage x weed management interaction (Table 7) . In 1994, soybean yielded 2.65 Mg ha^-1 in mechanical weed management under both tillage systems, which was 12% less than the 3.02 Mg ha^-1 yield in chemical weed management under chisel tillage and 9% less than the 2.92 Mg ha^-1 yield under moldboard plow tillage. Weed densities did not differ among weed management systems under moldboard plow tillage, so the 9% yield difference was probably associated with the 0.38-m row spacing in chemical compared with 0.76-m row spacing in mechanical weed management (Cox, 1995). Likewise, in 1995, the 13% lower yield in mechanical and chemical–mechanical compared with chemical weed management under moldboard plow tillage probably was associated mostly with row spacing differences, because weed densities did not differ among weed management systems. Buhler et al. (1992) reported similar weed control and soybean yields between mechanical and chemical weed management systems under moldboard plow tillage in the first year of a 2-yr study, but 12% lower yield in the second year.

In 1996, soybean yielded the same in mechanical and chemical weed management under moldboard plow tillage, but 10% less in mechanical weed management than chemical weed management under chisel tillage. Soybean thus yielded consistently less in mechanical than in chemical weed management in chisel tillage, averaging 22% less across years. Buhler and Gunsolus (1996) reported that soybean yielded 27% less in mechanical than chemical weed management under chisel tillage. Averaged across years, soybeans yielded only 7% less in mechanical than in chemical weed management under moldboard plow tillage. Weed densities did not differ among weed management systems, so the 7% yield difference was probably associated with row spacing differences. Averaged across years, moldboard yielded 12% more than chisel tillage, probably because of lesser weed densities, especially in chemical–mechanical and mechanical weed management.

Weed management costs averaged $114.60 ha^-1 for chemical, $73.60 ha^-1 for chemical–mechanical and $54.65 ha^-1 for mechanical management (Table 8) . Averaged across years, net returns showed a significant tillage x weed management interaction. Weed management systems did not affect soybean net returns under moldboard plow tillage (Table 8). Lower weed management costs in mechanical and chemical–mechanical compared with chemical weed management offset the 0.14 to 0.21 Mg ha^-1 lower yield. The substitution of the rotary hoe and two cultivations for broadcast herbicides under moldboard plow tillage thus resulted in similar soybean net returns, despite the use of wider row spacing for cultivation.

View this table: [in this window] [in a new window]   Table 8 Weed management costs and net returns of soybean, averaged across years (1994–1996), in chemical, chemical–mechanical, and mechanical weed management systems under moldboard and chisel tillage (Aurora, NY)

	Conclusion

TOP ABSTRACT INTRODUCTION Materials and methods NOTES Results and discussion Conclusion REFERENCES

 
We evaluated chemical, chemical–mechanical, and mechanical weed management systems in corn and soybean under moldboard plow and chisel tillage. Mechanical weed management generally had lesser weed density and greater relative yield in soybean than corn, and under moldboard plow than chisel tillage. For example, mechanical compared with chemical weed management in soybean under moldboard plow tillage had the same weed density, averaged 0.21 Mg ha^-1 lower yield, and had the same net return. In contrast, mechanical compared with chemical weed management in soybean under chisel tillage had greater weed density, averaged 0.62 Mg ha^-1 lower yield, and had $65 ha^-1 lower net return. Soybean growers who use moldboard plow tillage apparently can adopt any of the three weed management systems and receive equal net returns under environmental conditions of this study. Soybean growers who use chisel tillage, however, can expect similar net returns only with chemical–mechanical and chemical weed management systems.

Mechanical compared with chemical weed management in corn under moldboard plow tillage had greater weed densities in 1 of 3 yr and lower yield in 2 of 3 yr, and averaged $68 ha^-1 lower net return. Mechanical compared with chemical weed management in corn under chisel tillage had greater weed density in all years, averaged 1.6 Mg ha^-1 lower yield, and averaged $161 ha^-1 lower net return. Chemical–mechanical and chemical weed management had similar returns within tillage systems, so corn growers can expect similar net returns using either weed management system under environmental conditions of this study. If the USDA and USEPA wish to achieve implementation of IPM practices on 75% of the crop area by 2000, corn and soybean growers should be encouraged to adopt chemical–mechanical weed management systems. Growers who use chisel tillage, however, will have a greater challenge, because of the potential for greater weed densities in chisel tillage (Buhler, 1995).New York Agricultural Statistics 1997; Pennsylvania Agricultural Statistics 1996; SAS Institute 1991

	NOTES

TOP ABSTRACT INTRODUCTION Materials and methods NOTES Results and discussion Conclusion REFERENCES

 
¹ Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty for the product, and does not imply its approval to the exclusion of other products or vendors that may also be suitable.

	REFERENCES

TOP ABSTRACT INTRODUCTION Materials and methods NOTES Results and discussion Conclusion REFERENCES

 

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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 Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Cox, W. J. Articles by Bergstrom, G. C. Search for Related Content PubMed Articles by Cox, W. J. Articles by Bergstrom, G. C. Agricola Articles by Cox, W. J. Articles by Bergstrom, G. C.