Published in Agron. J. 96:1216-1221 (2004).
© American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Production Paper
Sod-Seeding and Grazing Effects on Alfalfa Weevils, Weeds, and Forage Yields in Established Alfalfa
D. Chad Cummingsa,*,
Richard C. Berberetb,
Jim F. Stritzkea and
John L. Caddela
a Dep. of Plant and Soil Sci., Oklahoma State Univ., 273 Agriculture Hall, Stillwater, OK 74078
b Dep. of Entomol. and Plant Pathol., Oklahoma State Univ., 273 Agriculture Hall, Stillwater, OK 74078
* Corresponding author (daniecc{at}mail.pss.okstate.edu)
Received for publication April 4, 2002.
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ABSTRACT
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Alfalfa (Medicago sativa L.) hay production for dairy and equine industries is a profitable enterprise in the Great Plains. However, as stands thin, forage production decreases and weeds increase, resulting in decreased returns. The objective of this research was to determine if alternative management strategies using October sod seeding plus March grazing could be utilized to increase forage production and control pests. Experiments were conducted at four locations in central Oklahoma from 1998–2000. Two ungrazed treatments (with and without pesticides) were compared with three treatments without pesticides but grazed by cattle in March. The three grazing treatments included: no sod seed, ryegrass (Lolium multiflorum Lam.) sod-seeded in October, and wheat (Triticum aestivum L.) sod-seeded in October. Grazing by cattle reduced alfalfa weevil (Hypera postica Gyllenhal) larval populations as effectively as insecticide application. In thin stands (<200 stems m–2), total forage yields were increased with alfalfa–grass mixtures by an average of 2.7 kg ha–1. However, alfalfa yields were decreased 0.9 kg ha–1 with sod-seeded ryegrass (P = 0.05). In thin stands, sod-seeded grass treatments were more effective at weed suppression than a herbicide treatment. Net returns from cool-season forage production increased with sod seeding plus March grazing compared with net returns using conventional haying methods. In thin stands (<200 stems m–2), sod seeding of ryegrass or wheat plus March grazing provided greater net returns ($175 ha–1) than conventional practice of using pesticides and haying. In full stands (>250 stems m–2), net returns from conventional alfalfa management (using pesticides and only haying) were comparable to October sod seed plus March grazing treatments.
Abbreviations: ADF, acid detergent fiber • AU, animal units • CP, crude protein • DM, dry matter • TDN, total digestible nutrients
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INTRODUCTION
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ALFALFA IN THE southern Great Plains is grown primarily to produce high quality, weed-free hay for dairy and equine industries. A full stand of alfalfa (>250 stems m–2) is competitive with weeds (Ward et al., 1990). However, as alfalfa stands decline, primarily resulting from plant diseases and insect damage, reduced alfalfa plant populations are not competitive enough to suppress weeds. During initial stages of stand decline as weed biomass becomes a measurable component, investment in herbicides to reduce weed interference can be profitable (Ward et al., 1990). However, when stem densities decline below 200 stems m–2, alfalfa production is significantly reduced (Cummings et al., 1999). At this point, sod-seeding a cool-season annual grass may increase desirable forage production and provide some increased competition to weeds.
Alfalfa weevils are a perennial pest in the southern Great Plains that can damage the first crop of alfalfa and contribute to stand decline (Dowdy et al., 1993). Berberet et al. (1987) reported that alfalfa weevil larval feeding results in defoliation of alfalfa plants, decreases the competitive ability of alfalfa against cool-season weeds, and contributes to stand decline. Reduced alfalfa plant populations allow weeds to grow and occupy open spaces in the plant canopy with resulting decreases in alfalfa forage quality (Undersander et al., 2001). The two types of pests, weeds and alfalfa weevils, often act in combination to produce greater reductions in alfalfa yields and stands than either pest may cause alone (Berberet et al., 1987; Norris et al., 1984).
Livestock grazing may have merit as an alternative method of pest control in alfalfa. Buntin and Bouton (1996) reported that populations of the alfalfa weevil larvae were reduced 60% in 1993 and 45% in 1994 by livestock grazing during winter and spring. They attributed this to consumption of eggs and larvae on consumed foliage of alfalfa and cool-season weedy grasses. Grazing is not normally utilized as a harvest option for pure alfalfa stands because there is greater profit potential in selling dairy quality hay (Caddel, 1997; Guerrero and Marble, 1991).
Alfalfa producers need to assess the profitability of applying herbicides and continuing to produce dairy quality hay when stands start to decline (fourth or fifth year of production in Oklahoma). Jung et al. (1996) reported that alfalfa interseeded with perennial ryegrass (Lolium perenne L.) provides high quality forage for both cow-calf and stocker cattle production systems since beef cattle only require between 12 and 14% crude protein (CP) for sustained growth (Natl. Res. Counc., 1996). They reported that CP of the alfalfa–ryegrass was only 2% lower than for alfalfa alone (20 vs. 22% CP). Sod-seeding cool-season grasses into thin alfalfa stands and focusing on producing forage for beef cattle may provide some additional years of profitable forage production.
The first objective of our research was to evaluate sod seeding of cool-season grasses plus grazing to control weeds and alfalfa weevils and increase cool-season (March–May) forage production in declining alfalfa stands. The second objective was to compare returns from October sod seeding with annual grasses plus March grazing with conventional hay production using pesticides in both thin and full stands of alfalfa.
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MATERIALS AND METHODS
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Three experiments on thin stands were conducted in 1998–1999 at locations near Chickasha, Paoli, and Tabler, OK. Experiment 1 (Chickasha) was located on the South Central Agronomy Research Station on a 6-yr-old, supplemental irrigated stand of ‘Garst 630’ alfalfa on Reinach silt loam soils (coarse-silty, mixed, superactive, thermic Pachic Haplustolls). Experiment 2 (Paoli) was on a 5-yr-old, nonirrigated stand of ‘Cimarron VR’ alfalfa on Konsil loamy fine sand soils (fine-loamy, siliceous, thermic Ultic Paleustalfs). Experiment 3 (Tabler) was on a 7-yr-old, nonirrigated stand of Cimarron VR alfalfa on Port silt loam soils (fine-silty, mixed, superactive, thermic Cumulic Haplustolls). Experiment 4 was conducted near Stillwater, OK, in 1999–2000 on a nonirrigated 4-yr-old full stand (267 stems m–2) of Cimarron VR alfalfa on Easpur silt loam soils (fine-loamy, mixed, superactive, thermic Fluventic Haplustolls).
A randomized complete block design was used for all experiments with either three or four replications. Experimental units (plots) were 4.6 by 9.1 m at Chickasha and Stillwater and 10.6 by 30.4 m at Paoli and Tabler locations. The five treatment combinations at each location included (i) no pesticides for weed or insect control, no sod seeding, and no grazing (designated ungrazed–no pesticides); (ii) application of terbacil (3-tert-butyl-5-chloro-6-methyluracil) (0.56 kg a.i. ha–1) herbicide, dormant season in February, and the insecticide cyfluthrin [cyano(4-fluoro-3-phenoxyphenyl)-methyl-3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylate] (0.045 kg a.i. ha–1) in March, with no sod seeding and no grazing (ungrazed–pesticides); (iii) grazing with no pesticides and no sod seeding (grazed–no pesticides); (iv) grazing with no pesticides and sod-seeded in October with ‘Marshall’ ryegrass (sod-seeded ryegrass; 13.4 kg ha–1); and (v) grazing with no pesticides and sod-seeded in October with ‘Tonkawa’ wheat (sod-seeded wheat; 134 kg ha–1). A broadcast application of diammonium phosphate at 112 kg ha–1 was made on all treatments at the time of sod seeding. A tractor-drawn, five-row, small double-disk seed drill with 0.3-m row spacing was used to sod-seed the annual grasses. A bicycle sprayer with CO2 gas propellant and 51-cm nozzle spacing was used to apply herbicide and insecticide treatments at 187 L ha–1. The dates for sod seeding and pesticide applications are given in Table 1.
Alfalfa weevil larval populations were sampled at 1- to 2-wk intervals during March and April by taking 25 alfalfa stems from each plot. Larval extraction was conducted with standard Berlese funnels. When larval populations reached the economic threshold of 1.0 to 1.5 larvae per stem (Berberet et al., 1981; Berberet and Mulder, 1993), the insecticide application was made to the ungrazed–pesticides treatment at each location. When alfalfa height reached 10 to 15 cm, short duration–high intensity grazing was initiated on the three grazed treatments. By 22 Feb. 1999, alfalfa weevil larval populations on some plots exceeded five larvae per stem before the alfalfa had sufficient growth to consider grazing on Exp. 2 and Exp. 3. To reduce weevil populations and prevent complete defoliation before alfalfa growth reached 10 to 15 cm for initiation of grazing, each of these experiments was oversprayed on 22 Feb. 1999 with permethrin [(3-phenoxyphenyl)methyl (±) cis-trans 3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylate] at 0.11 kg a.i. ha –1. This application was successful in achieving sufficient reduction in the alfalfa weevil larval populations below economic thresholds to allow some alfalfa growth for grazing.
Before March grazing, percentages of forage in each plot composed of alfalfa, sod-seeded grass, weedy grasses (Bromus tectorum L.), and broadleaf weeds [primarily Capsella bursa-pastoris (L.) Medic] were visually estimated. The amount of forage available for grazing was determined by clipping vegetation above 6-cm height from two 0.42-m2 quadrats randomly placed in each plot. Samples were oven-dried (52°C) for 10 d and then weighed for determination of dry matter (DM) production. At the initiation of grazing, the alfalfa was in early stages of vegetative growth (10–15 cm in height). Most weedy grasses and broadleaf weeds were still in vegetative growth stage. Hereford and Hereford-Angus/Brangus cross stockers weighing from 360 to 550 kg were used as grazing animals. Stocking rates and grazing periods varied at each location as a function of available forage and alfalfa weevil larval infestation (Table 1). Stocking rates ranged from 3.7 animal units (AU) ha–1 to 9.4 AU ha–1. March grazing periods ranged from 9 to 27 d. Grazing termination occurred when vegetation height was 6 cm and alfalfa weevil larval suppression had been achieved (Table 1).
Following the March grazing period, all additional cool-season forage was mechanically harvested. Before mechanically harvesting, percentages of forage composed of alfalfa, sod-seeded grass, weedy grasses (Bromus spp.), and broadleaf weeds [C. bursa-pastoris (L.) Medic] were visually estimated. Alfalfa stand densities (stems m–2) were estimated before the first mechanical harvest by counting stems in four 0.15- by 0.61-m quadrats at random in each plot. Stand densities were assessed in Exp. 4 during April 2001 to evaluate long-term effects of sod seeding on a full stand. Forage yield for each plot was determined by taking a 1- by 5-m forage sample from all plots with a Carter Forage Harvester. This sample was weighed immediately to get an actual field weight. From each harvested sample, a subsample of approximately 400 g was oven-dried (52°C) for calculations of DM production. Percentages of alfalfa, sod-seeded grass, weedy grass, and broadleaf weeds, estimated before harvesting, were used to calculate dry DM production for each forage component. Harvest dates are listed in Table 1.
Crude protein, acid detergent fiber (ADF), and neutral detergent fiber were determined from samples taken at first mechanical harvest by the analysis procedures of Undersander et al. (1993). Total digestible nutrients (TDN) were calculated using ADF values (Caddel and Allen, 1994; Zhang et al., 1998).
A partial budget was calculated on the March–May forage production to compare returns for each plot in all locations. All input and return considerations are partial analyses modified from the 1997 budget plans for dryland alfalfa production, calculated and distributed by the Oklahoma State University Department of Agricultural Economics and Oklahoma Cooperative Extension Service (Sahs et al., 2001) (Table 2). Costs for sod-seeding ryegrass and wheat and the use of pesticides were included in the analysis. Swathing, baling, and hauling costs all depended on yield and were assigned to all mechanical hay harvests. Inputs for sod-seeding the wheat and ryegrass were also considered.
Because of the various scenarios involving grazing and equipment ownership, a few assumptions were used in the partial budget for comparisons of returns among treatments. The producer owned all sod-seeding and harvest equipment, and values are presented for costs associated with the machinery use. Also, a cost of $29.21 Mg–1 (a cost equivalent to the swathe and baling cost) was applied to grazed treatments to cover the cost of labor, equipment, poloxalene, and dry hay for bloat control. In addition, all yields (grazed and hayed) were considered under the same forage value scale explained below.
A value for gross returns from forage production was calculated for each plot, based on the visually estimated composition of weeds and sod-seeded grass as price determinants. A base price for hay with less than 5% weeds or sod-seeded grass was set at $90 Mg–1, which is a representative amount paid for dairy quality hay in the southern Great Plains region. For each 15% interval in weed composition over the initial 5%, a $9 Mg–1 discount was subtracted from the base price. The lowest value for hay after the weed discount (more than 70% weeds) was $45 Mg–1. A similar price discount was used for increases in the sod-seed component. A $9 Mg–1 discount was subtracted for each increase of 40% sod-seeded grass composition above the initial 5% in the forage produced per plot. The lowest value for hay after the discount for sod-seeded grass (more than 50% sod-seeded grass) was $72 Mg–1. It was possible to receive a discount for weeds and sod-seeded grass.
After forage values had been allocated for each plot, variable costs (costs associated with individual treatments) and fixed costs (costs associated with the entire stand maintenance) were subtracted from gross returns to calculate net returns above investment. Data analyses were performed on gross returns, variable costs, and net returns for all plots in thin and full stands. The February application of terbacil and the cyfluthrin application were considered for pesticide costs in the ungrazed–pesticides treatment only.
All data from thin stands at Chickasha, Paoli, and Tabler locations were pooled since there were no significant location x treatment interactions for any of the data. Data from the full stand (257 stems m–2) at Stillwater were analyzed separately. All data were subjected to the analysis of variance using the MIXED procedure (SAS Inst., 1998). Location was designated as a random effect, and treatment was considered a fixed effect in the analyses. Means were separated with Student's t test for differences among treatments.
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RESULTS
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Hatching of alfalfa weevil larvae in thin stands in 1999 began during midwinter and averaged from 3.1 to 4.6 larvae stem–1 in the various treatments on 24 Feb. 1999 when cyfluthrin was applied to the ungrazed–pesticides treatment (Table 3). This application was quite effective, and the mean larval number across the experiments for this treatment was only 0.2 larvae stem–1 at grazing initiation in March. Application of permethrin on all treatments at Paoli and Tabler produced the desired effect in that larval numbers were reduced but remained above the economic threshold of 1.0 to 1.5 larvae stem–1 when grazing was initiated. Increased population of larvae resulted with ryegrass and wheat sod-seed treatments in thin stands (Table 3). The highest larval population at the time of cyfluthrin application was 4.6 larvae stem–1 in the sod-seeded ryegrass treatment, and this was greater than the larval population on stems in the grazed–no pesticides treatment. At grazing initiation in March, the larval populations in both the sod-seeded ryegrass and wheat (3.4 and 3.1 larvae stem–1, respectively) were higher than all other treatments. Grazing provided a substantial reduction in weevil numbers. When March grazing was terminated, mean larval numbers for the grazed–no pesticides, sod-seeded ryegrass, and sod-seeded wheat treatments ranged from 0.2 to 0.5 larvae stem–1. This level was below the economic threshold and comparable to the level of infestation in the ungrazed–pesticides treatment. Although hatching of the weevils was completed and many larvae had spun cocoons by the time grazing was terminated, the mean larval number of the ungrazed–no pesticides was still 1.5 larvae stem–1.
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Table 3. Effects of insecticide, March grazing, and October sod seeding on alfalfa weevil larval populations in the first crop of alfalfa in thin and full stands of alfalfa.
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Mean numbers of alfalfa weevil larvae were higher in the full stand compared with the thin stands (Table 3). However, hatching of larvae began later, and the potential for damage was not severe enough to prevent alfalfa from reaching sufficient height for grazing. Weevil numbers in the full stand were reduced from 7.0 larvae stem–1 at cyfluthrin application on the ungrazed–pesticides treatment to 0.1 larvae stem–1 on the date that grazing treatments were initiated. Weevil numbers in the sod-seed treatments were reduced from 4.0 and 5.0 larvae stem–1 at grazing initiation, for ryegrass and wheat, respectively, to only 0.7 and 0.8 larvae stem–1 after the cattle were removed from the grazed treatments. When compared with the mean larval number of 3.9 larvae stem–1, in the ungrazed–no pesticides treatment, these results also indicate the effectiveness of grazing for alfalfa weevil reduction.
Alfalfa stem counts taken at the time of the first mechanical harvest in each treatment reflect the additive effects of alfalfa weevil infestation, competition of sod-seeded grasses and/or weeds, and grazing among the varied treatments. In the thin stands, the largest mean stem density (157 stems m–2) resulted in the ungrazed–pesticides treatment (Table 4). With this treatment, there was considerable production of aboveground biomass of weeds (1.8 Mg ha–1) (Table 5) but minimal damage by weevils and no effects of grazing or competition from sod-seeded grasses. The smallest alfalfa stem density (75 stems m–2) resulted in the sod-seeded ryegrass treatment. Other treatments in thin stands had comparable stem densities. In the full stand, the only significant stand reduction resulted from the competitive effects of the sod-seeded ryegrass (Table 4).
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Table 4. Effects of grazing, sod-seeding, and pesticide treatment on alfalfa stem density at first mechanical harvest in thin and full stands of alfalfa.
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Table 5. March–May forage dry matter yields of alfalfa, weeds, sod-seeded grass, and total March–May forage yields in thin and full stands of alfalfa.
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March–May alfalfa production in thin stands was greatest in ungrazed–pesticides and sod-seeded wheat treatments (Table 5). However, as a result of low alfalfa stem densities, and large weeds that were not adequately controlled with terbacil, weeds still made up 44% of the March–May forage yields in the ungrazed–pesticides treatment. Weeds were the major forage component in the ungrazed–no pesticides treatment (2.9 Mg ha–1). This was attributed to decreased alfalfa competition resulting from alfalfa weevil feeding damage on the first crop of alfalfa. March–May weed yields in thin stands were lowest in the ryegrass and wheat sod-seeded treatments (0.6 and 0.7 Mg weeds ha–1). Sod-seeded grass made up 75 and 59% of the total forage yields for the sod-seeded ryegrass and wheat treatments, respectively, and provided significantly more forage for early-spring utilization than the other treatments.
In the full stand, March–May alfalfa yields were decreased by both sod-seed treatments plus March grazing compared with the ungrazed–pesticides and grazed–no pesticide treatments (Table 5). In addition, March–May weed yields were also reduced by both sod-seed treatments plus March grazing, with weed suppression being equal to the ungrazed–pesticides treatment. Due to competitiveness of alfalfa in the full stand, forage yields of sod-seed component were drastically decreased compared with results in thin stands.
In thin stands, the CP of the forage at first mechanical harvest was higher in the ungrazed– pesticides treatment than all other treatments (Table 6). However, there were no differences in levels of TDN among treatments in thin stands. In the full stand, sod-seeded ryegrass had lower CP than all other treatments. In addition, the TDN level of the grazed–no pesticides treatment was less than the ungrazed treatments and wheat sod-seeded and March grazed treatment.
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Table 6. Effects of grazing, sod-seeding, and pesticide treatment on crude protein (CP) and total digestible nutrients (TDN) in forage from thin and full stands of alfalfa.
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In thin stands, gross and net returns associated with March–May forage production were higher for the sod-seeded plus March grazing treatments than the ungrazed treatments (Table 7). In the full stand, there were no differences in gross returns among the treatments ($316 to $388 ha–1), but some higher net returns resulted, and this was attributed to decreased variable cost. The two treatments with the highest net return were the no pesticide–grazed and no pesticide–ungrazed treatments.
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Table 7. Effects of grazing, sod-seeding, and pesticide treatment on net returns of March–May forage yields from thin and full stands of alfalfa.
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DISCUSSION
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In the southern Great Plains, production of dairy quality hay from pure alfalfa stands is the standard against which all other forage systems are measured. Maintaining pure alfalfa stands not only increases the potential for high quality forage production, but also increases stand life and the potential profitability by providing marketing alternatives. When stands decline, growers must decide whether additional years of stand life are profitable, based on production levels and the cost of inputs.
Wolfson and Yeargan (1983) reported that weevil larval populations were greater in pure alfalfa than in thin, weedy stands. Altieri and Whitcomb (1979) noted greater insect predator numbers in horticulture crops infested with weeds. Thus, increased larval mortality in the weedy alfalfa stands could be due to increased number of insect predators. By sod-seeding, we changed the plant species diversity from one of a weedy alfalfa stand, with many plant species represented, into essentially a two-species community of alfalfa and sod-seeded grass. Another possibility is that sod-seeding the cool-season grasses increased canopy cover and resulted in a microclimate similar to that of a full stand of alfalfa.
Both winter and spring grazing have been used as effective alternatives to pesticide applications to reduce weevil habitat and larval populations and to prevent serious damage to alfalfa stands (Buntin, 1989; Buntin and Bouton, 1996; Latheef et al., 1992; Senst and Berberet, 1980). In our studies, timely spring grazing was as effective as pesticide application for weevil larval suppression (Table 3).
When alfalfa stem densities decline, sod-seeding annual grasses could provide some weed suppression and increased forage yields. In these studies, sod-seeding coupled with grazing decreased weed production and reduced the need for herbicide use in thin alfalfa stands (<200 stems m–2). Undersander et al. (2001) concluded that the competitiveness of the sod-seeded cool-season grasses decreased the available growth space for cool-season weeds. The annual sod-seeded ryegrass treatment in these experiments increased total forage yields by 3.1 kg ha–1 compared with the ungrazed–pesticides treatment. However, annual ryegrass may be too competitive because it decreased stem density in thin and full stands 52 and 22%, respectively, and suppressed alfalfa yield 41 and 44%, respectively, when compared with the ungrazed–pesticides treatment.
Crude protein and total CP yield have decreased when alfalfa was sod-seeded with cool-season grasses compared with alfalfa alone (Jung et al., 1996; Pike and Stritzke, 1984; Temme et al., 1979). In our study, the CP of both sod-seeding treatments was significantly (P < 0.05) decreased compared with ungrazed–pesticides treatment in thin stands. However, in the full stand, only the sod-seeded annual ryegrass resulted in a significant decrease in CP.
In thin stands, the combination of sod-seeding a cool-season grass plus March grazing resulted in the best net returns. These two treatments provide significantly more total desirable forage production, and costs of pesticides were reduced. This indicates that March grazing should provide a good alternative for pest control when cool-season weeds make up a significant part of the available forage. Weeds would be utilized and insects controlled by the grazing. Harvesting of April and May forage in stands that have been sod-seeded or that are infested with weeds should also increase net returns. In addition, having a grass component in alfalfa also appears to decrease the livestock bloat problem (Caddel et al., 2001).
Sod-seeded wheat appears to be the best choice for alfalfa growers in southern Great Plains to extend alfalfa stand productiveness. While ryegrass had higher production in our experiments, there were higher net returns associated with the sod-seeded wheat treatment. In addition, planting ryegrass is not recommended in wheat growing areas since ryegrass is a major weed problem in wheat grown for grain.
Alfalfa stem density is an important consideration regarding the potential for increased returns with sod-seeding cool-season grasses. If alfalfa stem density is near 250 stems m–2, the best option is to target production of dairy quality alfalfa hay and use conventional alfalfa management practices including pesticides. Increased gross returns from season-long, pure alfalfa production are sufficient to compensate for the expense of chemical pest control. As alfalfa stand density decreases to less than 200 stems m–2, higher net returns could be realized by sod-seeded cool-season grass and March grazing.
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ACKNOWLEDGMENTS
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The authors thank Don Hooper and staff of the OSU Agronomy Research Stations; Jeff Fassett and James Enis of the OSU Department of Plant and Soil Sciences; and Roger Sahs of the OSU Agricultural Economics Department. In addition, appreciation is expressed to Art Bisges and Ali Zarrabbi of the OSU Department of Entomology and Plant Pathology for their help and support for the duration of these experiments.
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NOTES
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This work has been approved for publication by the director of the Oklahoma Agricultural Experiment Station and supported in part under projects H-1527 and H-2294.
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INTRODUCTION
