Agronomy Journal 92:754-760 (2000)
© 2000 American Society of Agronomy
INTEGRATED PEST MANAGEMENT
Cropping System Effects on Weed Emergence and Densities in Corn
Jeremy W. Singera,
William J. Coxb,
Russell R. Hahnb and
Elson J. Shieldsb
a Dep. of Plant Science, Rutgers Univ., New Brunswick, NJ 08901 USA
b Dep. of Entomology, Cornell University, Ithaca, NY 14853 USA
wjc3{at}cornell.edu
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ABSTRACT
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The USDA has a goal of implementing integrated pest management (IPM) practices on 75% of the cropland in the USA so growers may adopt weed control practices that emphasize crop rotation and cultivation. Our objectives were to estimate weed densities in corn (Zea mays L.) and to examine weed emergence in an unmanaged weed area of corn following 4 yr of continuous corn, which received preemergence broadcast herbicides, and following soybean [Glycine max (L.) Merr.]–corn and soybean–wheat (Triticum aestivum L.)/red clover (Trifolium pratense L.)–corn cropping systems, which received banded herbicides and cultivation, on four farms in New York. More total weeds emerged at two sites and more perennial weeds emerged at all sites in the unmanaged weed area of corn in the soybean–wheat/red clover–corn cropping system compared with continuous corn because of poor red clover establishment, which resulted in a fallow period after wheat harvest. Weed densities in corn averaged 6.3 and 9.9 weeds m-2 in the soybean–wheat/red clover–corn cropping system, compared with 1.7 and 1.0 weeds m-2 in continuous corn at two of the sites, because of greater weed emergence and unsatisfactory weed control with banded herbicides and a single cultivation in the soybean–wheat/red clover–corn cropping system. When red clover does not establish well, growers should expect increased weed densities in the subsequent corn crop. Growers should then consider fall tillage or herbicide application after wheat harvest, or additional cultivation(s) or herbicide applications in the subsequent corn crop.
Abbreviations: IPM, integrated pest management • Vn, nth leaf stage of corn
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INTRODUCTION
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THE 1996 Federal Agriculture Improvement and Reform Act gradually eliminates government payments for grain crops. Continuous corn will probably decrease in the near future because of the lack of profitability in the absence of government payments. Also, the USDA and USEPA stated a goal of implementing IPM practices on 75% of the cropland in the USA by the year 2000 (USDA, 1993). Consequently, growers may adopt IPM practices in weed management that emphasize cultural weed control, such as crop rotation, and mechanical weed control, such as cultivation. Growers require more information on how cropping systems that emphasize crop rotation and cultivation for weed control affect weed emergence and subsequent weed densities in their crops.
Continuous cropping generally results in the least diversity in weed species, whereas crop rotation usually results in more weed diversity (Liebman and Dyck, 1993). For example, Covarelli and Tei (1988) observed that a corn–wheat rotation resulted in a diverse number of weed species in corn, whereas continuous corn resulted in one species that represented 71% of the total weeds. Ball and Miller (1990), who evaluated continuous corn, continuous pinto bean (Phaseolus vulgaris L.), and a sugarbeet (Beta vulgaris L.)–corn–corn rotation, reported that herbicide selection in each crop produced a shift in the weed seed bank in favor of species less susceptible to the applied herbicide. In particular, seed of hairy nightshade (Solanum sarrachoides Sendtn.) became prevalent in continuous pinto bean, whereas seed of kochia (Kochia scoparia L.), redroot pigweed (Amaranthus retroflexus L.), and common lambsquarters (Chenopodium album L.) became prevalent in the sugarbeet–corn–corn rotation. Mulugeta and Stoltenberg (1997), however, reported that densities of redroot pigweed and lambsquarters in corn did not differ between continuous corn and a soybean–corn rotation. Mulugeta and Stoltenberg (1997) attributed the lack of complexity in the soybean–corn rotation to the similar densities of these two weeds in continuous corn and in the soybean–corn rotation. Schreiber (1992) reported less giant foxtail (Setaria faberi R. Herrm.) in corn in a soybean–wheat–corn rotation compared with a soybean–corn rotation and continuous corn, because the wheat straw had an allelopathic effect on giant foxtail, thereby reducing giant foxtail densities in the subsequent corn crop.
Several studies during the last 10 yr have examined weed management systems in corn that use banded herbicides supplemented by cultivation (Mulder and Doll, 1993; Hartzler et al., 1993; Mt. Pleasant et al., 1994; Buhler et al., 1995; Krausz et al., 1995; and Mohler et al., 1997). The use of banded herbicides supplemented by cultivation generally resulted in similar or greater weed control in corn compared with preemergence broadcast herbicides. Environmental conditions during May and June, however, influenced the efficacy of preemergence broadcast herbicides and cultivation (Mulder and Doll, 1993; Mt. Pleasant et al., 1994; Buhler et al., 1995; Krausz et al., 1995).
Most studies in the literature that have evaluated the effects of crop rotation or cultivation on weed control have been conducted on university research farms, where previous weed management studies can influence the emergence of different weed species and subsequent weed densities. We developed farmer–researcher partnerships (Karlen et al., 1995), and conducted field-scale studies to determine the effect of different cropping systems on weed densities in corn typically encountered on New York cash grain farms. Our objective was to determine weed densities in continuous corn, which received preemergence broadcast herbicides, and in the corn phase of soybean–corn and soybean–wheat/red clover–corn cropping systems, which received banded preemergence herbicides supplemented by cultivation for weed control. Another objective of this study was to estimate total weed emergence and emergence according to life cycle and species in an unmanaged weed area to determine potential weed densities in corn after 4 yr of continuous corn, two cycles of soybean–corn, and one cycle of soybean–wheat/red clover–corn cropping systems.
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Materials and methods
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A 4-yr field study was established during the 1993 growing season on four farms across Central/Western New York. Participating farmers performed all field operations, including tillage and planting operations, herbicide and fertilizer applications, cultivation, and harvest operations. The predominant soil types are a Schoharie clay loam (fine, illitic, mesic Oxyaquic Hapludalf) at the Orleans and Seneca County sites, and a Honeoye silt loam (fine-loamy, mixed, active, mesic Glossic Hapludalf) at the Cayuga and Yates County sites. Corn had been grown at all four experimental sites in 1992.
Two tillage systems and three cropping systems were evaluated in a randomized complete block design in a split-plot arrangement with two replications at each site. Main plots, ranging from 32 to 64 m wide and from 122 to 335 m long, consisted of two primary tillage systems, moldboard plow and chisel tillage. Subplots, ranging from 4.6 m (6 rows of corn) at the Cayuga and Yates Co. sites to 9.1 m (12 rows) wide at the Orleans and Seneca Co. sites, consisted of continuous corn and soybean–corn (in both phases) and soybean–wheat/red clover–corn (in all three phases) cropping systems. Consequently, three corn crops (continuous corn and corn in the soybean–corn and soybean–wheat/red clover–corn cropping systems), two soybean crops (soybeans in soybean–corn and soybean–wheat/red clover–corn cropping systems), and one winter wheat crop were planted each year beginning in 1993 (Table 1)
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Table 1 Cropping systems and their different phases in 1993, 1994, 1995, and 1996 at all four sites. All sites were planted to corn in 1992
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Winter wheat was drilled at 0.18-m spacing after soybean harvest in early October at all sites. `Mammouth' red clover was frost-seeded into the wheat crop in March of each year at all sites as a green manure crop in the soybean–wheat/red clover–corn cropping system. After wheat harvest in July, the straw was baled at each site, except at Orleans Co. Red clover then grew rapidly in late summer and fall before being plowed under in either late fall or early spring. New York wheat producers typically do not apply herbicides in the spring to wheat overseeded with red clover because herbicide options are limited (R.R. Hahn, personal communication, 1993). Wheat also did not receive fall herbicides at any of the sites because of low weed density.
Pioneer Brand `3733' hybrid corn was planted with a starter fertilizer in early to mid-May at all sites in 1993, 1994, and 1995 at a row spacing of 0.76 m. Planting was delayed until late May at all sites in 1996 because of wet soil conditions. At about the 5-leaf (V5) stage (Ritchie et al., 1993), all sites received additional N as anhydrous ammonia injected about 0.1 m deep between rows. Herbicides that were applied to continuous and rotated corn at each site for the 1993, 1994, 1995, and 1996 growing seasons are listed in Table 2
. The participating farmers selected the herbicides based on their knowledge of potential weed species at each site. Continuous corn received broadcast preemergence herbicide applications at labeled rates, whereas rotated corn received a banded application (0.25 m) at planting at labeled rates, followed by a timely cultivation. Cultivation equipment varied at each site in make and model. Continuous corn also received a soil-applied insecticide at planting for corn rootworm control.
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Table 2 Herbicides used at labeled rates for continuous corn, rotated corn (soybean–corn and soybean–wheat/red clover–corn), and soybean at four sites in New York during the 1993, 1994, 1995, and 1996 growing seasons
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Pioneer Brand `9162', a mid-Group I soybean variety, was planted a few days after corn at all sites in each year. Soybeans were planted at 0.18-m row spacing at Orleans and Seneca Co. sites, at 0.38-m spacing at the Cayuga Co. site, and at 0.76-m spacing at the Yates Co. site. Preemergence broadcast herbicides that were applied to soybeans at labeled rates at each site are listed in Table 2 for the 1993, 1994, 1995, and 1996 growing seasons.
In 1993, the percent weed cover of individual weed species that were present outside the herbicide band between corn rows in soybean–corn and soybean–wheat/red clover–corn cropping systems before cultivation was estimated at each site by the beaded string method, as described by Mt. Pleasant et al. (1994). We were unable to estimate percent weed cover in continuous corn before preemergence herbicides were applied in early May. Consequently, we assumed that average percent weed cover, which was similar between the two cropping systems, would also represent percent weed cover for continuous corn. Weed species that had more than 25% weed cover were considered dominant weeds at the onset of the study.
Weed densities in corn were estimated in 1994, 1995, and 1996 after cultivation at about the V8 growth stage at each site, except at Orleans Co. in 1994, by counting all the weeds (greater than 5 mm in height) along the entire length of the two inner rows of each subplot. Weeds that were less than 5 mm in height were not counted because we did not believe that they would interfere with the growth and yield of corn. Weed species that represented 25% or more of the weed counts within cropping systems at each site were considered dominant.
Randomly selected unmanaged weed areas (no herbicide or cultivation), which ranged from 21 to 41 m2, were established in each corn phase of the three cropping systems at each site in 1996 to determine densities of different weed species that would emerge if no weed management practices were used. Two 0.5-m2 quadrats were established in each unmanaged weed area and sampled for weed density at approximate 2-wk intervals beginning 20 to 30 d after planting, for a total of four sampling dates at each site. Each quadrat was centered on a corn row and subdivided to measure weed density in and between rows. The sample area was divided into within and between corn rows to determine if different weed management practices within the row (banded herbicide) and between the row (cultivation) in the 1993 (soybean–wheat/red clover–corn) or 1994 corn crops (soybean–corn) had any effect on weed emergence in corn in 1996. After planting, there was no additional traffic or soil disturbance in the unmanaged weed areas.
Each weed seedling was identified, counted, and removed from the quadrat at each sampling date. Weeds were classified as either annual grass, annual broadleaf, or perennial weeds. Total weed emergence was calculated for the season by summing the densities of annual grasses, annual broadleaves, and perennials from each sampling date. Additionally, individual species at each site were counted and summed across sampling dates to determine total emergence of these species. Individual species that represented more than 10% of the total weeds that emerged were considered dominant.
All data were analyzed by analysis of variance procedures with the SAS Statistical Software Package (SAS Inst., 1990). Weed density did not have tillage x cropping system interactions in 1994, 1995, or 1996, so the data were averaged across tillage systems. Likewise, total weed emergence and emergence according to life cycle or individual species in the unmanaged weed area of corn in 1996 did not have tillage x cropping system interactions, so the data were averaged across tillage systems. Also, there were no row vs. interrow main effects or interactions for total weed emergence and emergence according to life cycle or individual species, so the data were averaged across row positions. Annual grass emergence at Cayuga Co., annual broadleaf emergence at Seneca Co., and perennial weed emergence at Yates Co. required transformation to adjust for heterogeneity of variances. Likewise, common lambsquarters emergence at Cayuga Co. and yellow nutsedge emergence at Yates Co. required transformation. Logarithmic transformation (base 10) equalized the variances best. Mean separation among treatment means for transformed and untransformed data were obtained by Fisher's protected LSD. Because most data did not require transformation, only untransformed means are presented. Also, regression equations were fitted for crop yields, as previously reported by Singer and Cox (1998), as a function of weed densities at each site in each year of the study with the General Linear Models (GLM) procedure of SAS. Effects were considered significant in all statistical calculations for P-values 
0.05.
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Results and discussion
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Dominant weed species that emerged at each site before cultivation in the interrow corn areas at the onset of the study in 1993 are presented in Table 3
. Yellow nutsedge (Cyperus esculentus L.) and common ragweed (Ambrosia artemisiifolia L.) at Orleans Co., quackgrass [Agropyron repens (L.) P. Beauv.] at Seneca Co., and redroot pigweed at Yates Co. remained dominant in corn in 1994, 1995, and 1996 within all three cropping systems, despite different weed control methods and crop rotations in each cropping system (Table 4)
. Also, green foxtail [Setaria viridis (L.) P. Beauv.] at Cayuga Co. and giant foxtail at Yates Co. became dominant in all three cropping systems in 1996. Weed control methods in corn in the three cropping systems provided satisfactory control of the dominant weeds and other weed species in 1994 and 1995, as indicated by relatively low weed densities in all cropping systems (Table 5)
. In fact, weed densities had nonsignificant correlations with crop yields at all sites in 1994 and 1995 (data not shown).
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Table 3 Dominant weed species between rows before cultivation in rotated corn at four sites in 1993 and in an unmanaged weed area of corn following continuous corn, soybean–corn, and soybean–wheat/red clover–corn cropping systems at four sites in 1996
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Table 4 Dominant weed species in corn in continuous corn, soybean–corn, and soybean–wheat/red clover–corn cropping systems at four sites in New York during the 1994, 1995, and 1996 growing seasons
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Table 5 Weed density in corn at the 8th leaf stage (V8) in continuous corn, soybean–corn, and soybean–wheat/red clover–corn cropping systems at four sites in New York during the 1994, 1995, and 1996 growing seasons
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Weed densities averaged 6.3 weeds m-2 in the soybean–wheat/red clover–corn cropping system, compared with 1.7 weeds m-2 in continuous corn and 1.5 weeds m-2 in the soybean–corn cropping system in 1996 at Orleans Co.. At Yates Co., weed densities averaged 9.9 weeds m-2 in the soybean–wheat/red clover–corn cropping system, compared with 2.6 weeds m-2 in the soybean–corn cropping system and 1.0 weeds m-2 in continuous corn. Weed control methods in corn in soybean–corn and soybean–wheat/red clover–corn cropping systems did not differ, so different weed control practices in the preceding soybean and wheat/red clover crops probably contributed to weed control differences in corn between these two cropping systems at the two sites. Weed densities averaged only 0.7 weeds m-2 in the soybean–wheat/red clover–corn cropping system, compared with 2.4 weeds m-2 in continuous corn at Cayuga Co., where the participating farmer cultivated twice because of weed emergence after the first cultivation. Unfortunately, wet soil conditions and large corn hectarages prevented participating farmers from performing a timely second cultivation at Orleans and Yates Co.. Although weed densities differed among cropping systems at three sites, weed densities had nonsignificant negative correlations with crop yields at all sites in 1996 (data not shown).
Most dominant weeds at the onset of the study remained dominant in the unmanaged weed area of corn within the three cropping systems in 1996, with two notable exceptions (Table 3). Dandelion (Taraxacum officinale Weber in Wiggers), a dominant weed at Cayuga and Yates Co. at the onset of the study, decreased in occurrence in all cropping systems at both sites by 1996. Dandelion is a simple perennial, so the use of moldboard plow or chisel tillage as well as cultivation in two of the cropping systems apparently reduced its occurrence, as also noted by Buhler et al. (1994). In contrast, densities of green foxtail at Cayuga Co. and giant foxtail at Yates Co. greatly increased in all cropping systems by 1996. Mulugeta and Stoltenberg (1997) also reported a dramatic increase in giant foxtail in a soybean–corn rotation and in continuous corn, especially under moldboard plow tillage.
Total weed emergence and emergence of annual grasses, annual broadleaves, and perennials in the unmanaged weed area of corn for the three cropping systems at each site in 1996 are presented in Table 6
. Emergence of some individual weed species in the unmanaged weed area for the three cropping systems at each site are presented in Table 7
. Row position did not affect weed emergence within the three cropping systems at the four sites (data not shown), so the use of cultivation vs. preemergence herbicides for interrow weed control in rotated corn (1993 in soybean–wheat/red clover–corn and 1994 in the soybean–corn cropping systems) apparently did not affect weed emergence in the unmanaged weed area in 1996. Crop rotation, which dictates herbicide use, timing of tillage events relative to crop and weed emergence, and harvest date relative to crop and weed maturity are the most important determinants of weed emergence and weed species composition over a period of several growing seasons (Ball and Miller, 1990). The preceding crops and associated weed control practices in those crops thus probably contributed most to the differences in emergence of total weeds, annual grasses, annual broadleaves, perennials, and individual species among cropping systems in 1996.
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Table 6 Emergence of annual grass, annual broadleaf, perennial, and total weeds in an unmanaged weed area of corn following continuous corn, soybean–corn, and soybean–wheat/red clover–corn cropping systems at four sites in New York during the 1996 growing season
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Table 7 Emergence of weed species in an unmanaged weed area of corn following continuous corn, soybean–corn, and soybean–wheat/red clover–corn cropping systems at four sites in New York during the 1996 growing season
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At Cayuga Co., a site with high weed emergence, more total weeds emerged in the soybean–corn cropping system (1264 m-2) compared with continuous corn (470 m-2), primarily because of greater annual grass (838 and 426 m-2, respectively) and broadleaf weed emergence (354 and 20 m-2, respectively). Although green foxtail represented 88% of total weed emergence in continuous corn compared with 50% in soybean–corn and 57% in soybean–wheat/red clover–corn, green foxtail emergence did not differ among cropping systems (data not shown). More large crabgrass (224 m-2) and common lambsquarters (50 m-2), however, emerged in the soybean–corn cropping system compared with continuous corn (16 and 4 m-2, respectively). Also, more perennial weeds emerged in the soybean–wheat/red clover–corn cropping system (145 m-2) compared with continuous corn (25 m-2), primarily because of greater plantain (Plantago major L.) emergence (112 and 8 m-2, respectively). More weed emergence in the unmanaged weed area indicated a potential for greater weed density in the soybean–corn and soybean–wheat/red clover–corn cropping systems compared with continuous corn. Surprisingly, continuous corn had greater weed densities when compared with the soybean–wheat/red clover–corn cropping system, presumably because banded herbicides plus two cultivations resulted in better green foxtail control than the use of preemergence herbicides in 1996 (Tables 4 and 5).
Cropping systems affected total weed emergence and weed emergence according to life cycle and species in the unmanaged weed area in corn at Orleans Co., a site with moderate weed emergence. More total weeds emerged in the soybean–wheat/red clover–corn cropping system (611 m-2) compared with continuous corn (233 m-2) and the soybean–corn cropping system (175 m-2), primarily because of greater annual grass (106, 2, and 4 m-2, respectively) and perennial weed emergence (334, 112, and 70 m-2, respectively). Specifically, more yellow nutsedge emerged in the soybean–wheat/red clover–corn cropping system (330 weeds m-2), compared with continuous corn (107 m-2) and the soybean–corn cropping system (65 m-2) at Orleans Co., a site well-adapted for yellow nutsedge because of the somewhat poorly drained soils (Stoller, 1981). Johnson and Mullinix (1997) reported that yellow nutsedge densities and tubers increase exponentially in fields under fallow weed management. Singer and Cox (1998) previously reported that red clover did not establish well at this site in 1995 because of very dry spring conditions. Consequently, after wheat harvest in July of 1995, the soybean–wheat/red clover–corn cropping system was in a fallow period from August through October. The late summer–early fall fallow period in 1995 may have increased yellow nutsedge emergence in the soybean–wheat/red clover–corn cropping system in 1996. Mohler et al. (1997) reported that timely and frequent cultivations were necessary for yellow nutsedge control because of its rapid early-season growth and establishment. Evidently, the increased weed emergence of yellow nutsedge and the use of a single cultivation for interrow weed control resulted in high yellow nutsedge densities in corn in the soybean–wheat/red clover–corn cropping system in 1996 (Tables 4 and 5).
Cropping systems did not affect total weed emergence in the unmanaged weed area of corn at Seneca Co., a site with relatively low weed emergence. More annual broadleaves, however, emerged in continuous corn (243 m-2) compared with the other cropping systems. Also, more perennial weeds emerged in the soybean–wheat/red clover–corn cropping system (44 m-2) compared with continuous corn (15 m-2) and the soybean–corn (14 m-2) cropping system, primarily because of greater quackgrass emergence (39, 12, and 11 m-2, respectively). Nevertheless, the relatively low weed emergence contributed to very low weed densities at this site in all three years of the study (Table 5).
Cropping systems affected total weed emergence at Yates Co., another site with high weed emergence. More total weeds (1494 m-2) and perennial weeds (98 m-2) emerged in the soybean–wheat/red clover–corn cropping system compared with continuous corn (560 and 2 m-2, respectively). Although giant foxtail represented 70% of the weeds in continuous corn compared with 52% in soybean–corn and 45% in soybean–wheat/red clover–corn cropping systems, giant foxtail emergence did not differ among cropping systems (data not shown). In New York, wheat growers typically harvest the wheat straw, thereby minimizing allelopathic effects of wheat residue on giant foxtail (Schreiber, 1992). New York wheat growers, however, typically interseed red clover into wheat in early spring as a green manure crop. Red clover is also an effective short-term smother crop (Liebman and Dyck, 1993), which can suppress weed growth after wheat harvest. Poor establishment of red clover at this site because of dry spring conditions resulted in a late summer–early fall fallow period in 1995, which apparently contributed to greater total and perennial weed emergence, specifically yellow nutsedge emergence (59 m-2) in the soybean–wheat/red clover–corn cropping system compared with the other two cropping systems (2 m-2). The greater emergence of total weeds and the use of banded herbicides plus a single cultivation resulted in very high weed densities in corn in the soybean–wheat/red clover–corn cropping system in 1996 (Table 5).
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Conclusion
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Cropping systems affected weed emergence in an unmanaged weed area of corn after 4 yr of continuous corn, two cycles of soybean–corn, and one cycle of soybean–wheat/red clover–corn cropping systems on four farms in New York. More total weeds emerged at two sites and more perennial weeds emerged at all sites in the unmanaged weed area of corn in 1996 in the soybean–wheat/red clover–corn cropping system compared with continuous corn. Weed control measures in the soybean–wheat/red clover–corn cropping system included preemergence banded herbicides plus a single cultivation in corn in 1993, preemergence broadcast herbicides in soybeans in 1994, cultural weed control (early fall planting, high seeding rates, and interseeded red clover) in wheat in 1995, and preemergence banded herbicides plus cultivation in corn in 1996. Red clover did not establish well in 1995 because of dry conditions, which resulted in a fallow period after wheat harvest and more weed emergence, especially perennial weed emergence, in the unmanaged weed area of corn in 1996. More weed emergence contributed to high weed densities in corn at two sites in the soybean–wheat/red clover–corn cropping system in 1996, because banded herbicides plus a single cultivation did not provide adequate weed control. When red clover does not establish well, growers should expect increased weed densities in the subsequent corn crop. Growers should then consider fall tillage or herbicide application after wheat harvest, or additional weed control measures such as cultivation(s) or postemergence herbicides in the subsequent corn crop.
Continuous corn, which received preemergence broadcast herbicides in all 4 years of the study, had 40 to 50% less total weed emergence in the unmanaged weed area in 1996 compared with the other two cropping systems, probably because annual applications of triazine herbicides can reduce the weed seed reservoir by 90% after 4 yr (Schweizer and Zimdahl, 1984). Nevertheless, participating farmers in this study achieved similar weed control in corn in continuous corn and soybean–corn cropping systems, despite the use of banded preemergence herbicides plus cultivation in corn in the soybean–corn cropping system. More total weeds, specifically annual grasses and annual broadleaves, emerged at one site in the unmanaged weed area of corn in 1996 in the soybean–corn cropping system compared with continuous corn. Consequently, growers may at times require additional weed control measures, such as a second cultivation, in corn in a soybean–corn cropping system, which relies on preemergence broadcast herbicides in soybean and banded herbicides plus a single cultivation in corn.SAS Institute 1990
Received for publication July 1, 1999.
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REFERENCES
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- Ball D.A., Miller S.D. Weed seed population response to tillage and herbicide use in three irrigated cropping sequences. Weed Sci. 1990;38:511-517.
- Buhler D.D., Doll J.D., Proost R.J., Visocky M.R. Integrating mechanical weeding with reduced herbicide use in conservation tillage corn production systems. Agron. J. 1995;87:507-512.[Abstract/Free Full Text]
- Buhler D.D., Stoltenberg D.E., Becker R.L., Gunsolus J.L. Perennial weed populations after 14 years of variable tillage and cropping practices. Weed Sci. 1994;42:205-209.
- Covarelli, G., and F. Tei. 1988. Effet de la rotation culturale sur la flore adventice du maîs. p. 477–484 In VIII Ième Colloque International sur la Biologie, l'Écologie et la Systématique des Mauvaises Herbes, Dijon, France. 14–16 Sept. 1988. A.N.P.P. Annales no. 3, vol. 2. Association Nationale pou la Protection des Plantes (Commission mauvaises herbes—COLUMA), Paris.
- Hartzler R.G., van Kooten B.D., Stoltenberg D.E., Hall E.M., Fawcett R.S. On-farm evaluation of mechanical and chemical weed management practices in corn (Zea mays). Weed Technol. 1993;7:1001-1004.
- Johnson W.C., III, Mullinix B.G., Jr. Population dynamics of yellow nutsedge (Cyperus esculentus) in cropping systems in the southeastern coastal plain. Weed Sci. 1997;45:166-171.
- Karlen D.L., Duffy M.D., Colvin T.S. Nutrient, labor, energy, and economic evaluations of two farming systems in Iowa. J. Prod. Agric. 1995;8:540-546.
- Krausz R.F., Kapusta G., Matthews J.L. Evaluation of band vs. broadcast herbicide applications in corn and soybean. J. Prod. Agric. 1995;8:380-384.
- Liebman M., Dyck E. Crop rotation and intercropping strategies for weed management. Ecol. Appl. 1993;3:92-122.
- Mohler C.L., Frisch J.C., Mt J., Pleasant Evaluation of mechanical weed management programs for corn. Weed Tech. 1997;11:123-131.
- Mt. Pleasant J., Burt R.F., Frisch J.C. Integrating mechanical and chemical weed management in corn (Zea mays). Weed Technol. 1994;8:217-223.
- Mulder T.A., Doll J.D. Integrating reduced herbicide use with mechanical weeding in corn (Zea mays). Weed Technol. 1993;7:382-389.
- Mulugeta D., Stoltenberg D.E. Weed and seedbank management with integrated methods as influenced by tillage. Weed Sci. 1997;45:706-715.
- Ritchie S.W., Hanway J.J., Benson G.O. How a corn plant develops. Ames: Iowa State Univ. Coop. Ext. Serv. Spec. Rep. no. 48. Iowa State Univ. Coop. Ext. Serv, 1993.
- SAS Institute. SAS user's guide. Statistics, 6th ed Cary, NC: SAS Inst, 1990.
- Schreiber M.M. Influence of tillage, crop rotation, and weed management on giant foxtail (Setaria faberi) population dynamics and corn yield. Weed Sci. 1992;40:645-653.
- Schweizer E.E., Zimdahl R.L. Weed seed decline in irrigated soil after six years of continuous corn (Zea mays) and herbicides. Weed Sci. 1984;32:76-83.
- Singer J.W., Cox W.J. Agronomics of corn production under different crop rotations in New York. J. Prod. Agric. 1998;11:462-468.
- Stoller E.W. Yellow nutsedge: A menace in the corn belt. Washington, DC: U.S. Gov. Print. Office, 1981 USDA Tech. Bull. No. 1642..
- USDA. Three-agency release: Presidential announcement regarding IPM adoption. Washington, DC: Office of Communications, 1993.
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ABSTRACT
INTRODUCTION
