Jeremy W. Singer

Alfalfa Living Mulch Advances Biological Control of Soybean Aphid

Abstract Despite evidence for biological control in North America, outbreaks of the invasive soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), continue to occur on soybean (Glycine max L. Merr.). Our objectives were to determine whether natural enemies delay aphid establishment and limit subsequent population growth and whether biological control can be improved by altering the within-field habitat. We hypothesized that a living mulch would increase the abundance of the aphidophagous community in soybean and suppress A. glycines establishment and population growth. We measured natural enemy and A. glycines abundance in soybean grown with and without an alfalfa (Medicago sativa L.) living mulch. Soybean grown with an alfalfa living mulch had 45% more natural enemies and experienced a delay in A. glycines establishment that resulted in lower peak populations. From our experiments, we concluded that the current natural enemy community in Iowa can delay A. glycines establishment, and an increase in aphidophagous predator abundance lowered the rate of A. glycines population growth preventing economic populations (i.e., below the current economic threshold) from occurring. Incorporation of a living mulch had an unexpected impact on A. glycines population growth, lowering the aphids’ intrinsic rate of growth, thus providing a bottom-up suppression of A. glycines. We suggest future studies of living mulches or cover crops for A. glycines management should address both potential sources of suppression. Furthermore, our experience suggests that more consistent biological control of A. glycines may be possible with even partial resistance that slows but does not prevent reproduction.

Effects of Living Mulches on Predator Abundance and Sentinel Prey in a Corn–Soybean–Forage Rotation

Abstract Living mulches are cover crops grown concurrently within main crops for their benefits to weed control and soil quality. Because living mulches increase the diversity of vegetation in agricultural systems, they may impact the abundance or effectiveness of natural enemies. To examine the effects of living mulches on epigeal predators, arthropod abundance and feeding were examined in a rotation of corn (Zea mays L.), soybean (Glycine max L. Merr.), and forage crops in 2004 and 2005. Compared with a no-mulch control, the presence of alfalfa (Medicago sativa L.) and kura clover (Trifolium ambiguum M. Bieb.) mulches in corn and soybean increased predator abundance and consumption of European corn borer (Ostrinia nubilalis Hübner; Lepidoptera: Crambidae) pupae used as sentinel prey. A complementary effect of increased predation caused by corn and soybean was found when both annual crops with living mulches were compared with mulches grown alone. Positive correlations between the percentage of O. nubilalis pupae preyed on and ground beetle (Coleoptera: Carabidae) abundance suggest carabids contributed to the differences in predation. In 2005, fewer beetles correlated with consumption of O. nubilalis pupae [Poecilus chalcites (Say) and Scarites quadriceps Chaudior] were collected, and living mulch impacts on predation were less frequent. Both changes could be related to delayed herbicidal suppression of the living mulches in 2005, which seemed to homogenize predator community composition among the corn, soybean, and forage plots. Although living mulches alone may not provide sufficient pest suppression, their potential to enhance biological control should be considered along with their other agronomic benefits.

Rye Cover Crop Management Affects Grain Yield in a Soybean-Corn Rotation

Cover crops provide environmental benefits, yet their adoption into production agriculture has been limited. The objectives of this study were to determine how rye (Secale cereale L.) cover crop management affects yield of soybean [Glycine max (L.) Merr.] and corn (Zea mays L.) in a soybean-corn rotation. Field studies were conducted from 2001 to 2004 near Boone, IA. Prior to soybean, rye was controlled chemically and mechanically at Feeke’s growth stages 7 (2nd node visible), 9.8 (boot), and 10.5.1 (flowering). Prior to corn, reseeded rye from mechanical control plots was chemically controlled. In 2002 and 2003, no soybean yield differences were detected among timing treatments in mechanical control, which yielded 21 and 29 compared to 52 and 42 bu/acre in the no-rye check. In the chemical control treatments, soybean yielded 30, 39, 43, and 50 bu/acre in the 2nd node, boot, flowering, and check in 2002 and 29, 30, 36, and 43 bu/acre in 2003. Corn yield following rye was lower than the check in 2003 (133 versus 153). In 2004, corn yield only differed between the flowering treatment and the check. These results indicate that alternative rye cover crop systems must be developed to protect soil and water resources and provide economic returns.

Corn Yield Response of and Near-Isolines to Plant Density

Optimum plant densities for Bacillus thuringiensis (Bt) corn (Zea mays L.) should be higher than non-transgenic corn subjected to European corn borer (ECB; Ostrinia nubilalis Hubner) damage because of the reduced potential for stalk lodging. The objectives of this research were to determine if yield differences occurred in Bt compared to near-isoline hybrids and to determine if different optimum densities exist for Bt and near-isolines. Bt hybrids were compared at target densities ranging from 20000 to 36000 plants per acre at different midAtlantic locations in 2000 and 2001. Yield increases ranged from 5 to 8% in 2000 at all locations. In contrast, Bt corn performed better than near-isolines at only one of three locations in 2001, with a 10% yield advantage. Relationships between yield of near-isolines and ECB damage were weak. Plant density affected yield at all locations in both years. Regression analysis of grain yield on plant density did not reveal a consistent hybrid response, although some evidence exists that suggests Bt hybrids are more efficient than near-isolines at producing yield as plant density increases. The inability to identify different optimum densities for Bt and near-isolines may have been due to low stalk lodging, plant density treatments that did not maximize yield in most instances, or the absence of different optimum densities.

Tall Fescue Response to Nitrogen and Harvest Date for Stockpiled Grazing in the Upper Midwest

Tall fescue (Festuca arundinacea Schreb.) is a cool-season grass with physiological and morphological traits suitable for stockpiled grazing. The effect of late summer nitrogen (N) application was measured for yield and quality responses using four N rates (0, 25, 50, and 100 lb/acre) and three autumn harvest dates. Averaged across harvest date, linear increases of dry matter (DM) occurred in 1999 and 2000. In 1999, yield = 1747 + 15 × N rate (R 2 = 0.92, RMSE = 235) and in 2000, yield = 672 + 19 × N rate (R 2 = 0.96, RMSE = 202). Year by harvest date and year by N rate interactions were observed for yield because of above average rainfall in 1999 and below average rainfall in 2000. Forage crude protein (CP) and in vitro dry matter digestibility (IVDMD) increased as N rate increased, while neutral detergent fiber (NDF) decreased. Year by harvest date interactions were observed for CP, NDF, and IVDMD, and year by N rate interactions were observed for CP and NDF. Late summer N application increased DM yield and CP of the first cutting the following spring. Forage producers who apply late-season N can increase the quantity and quality of tall fescue forage available for autumn grazing. However, yield and quality losses can occur if harvest is delayed beyond October.

Profitability of Various Corn, Soybean, Wheat, and Alfalfa Cropping Systems

Producers are frequently most interested in economic comparisons of various cropping systems. We compared continuous corn (Zea mays L.) and continuous soybean [Glycine max (L.) Merr.] with 2-, 3-, and 5-year rotations, the latter two including wheat (Triticum aestivum L.) and alfalfa (Medicago sativa L.), using either chisel plow or no-tillage practices. Crop yield and returns to land and management were evaluated. Yields for continuous corn (C-C-C) were not different from those in rotation [corn-soybean (C-S), soybean-wheat/soybeancorn (S-W/S-C), or corn-soybean-alfalfa-alfalfa-alfalfa (C-S-A-A-A)] for either tillage practice, but rotated corn had lower nitrogen (N) inputs. Soybean yield in the 5-year rotation was greater than for continuous soybean (S-S-S) in 2001 for both tillage practices, but in 2000, a tillage by rotation interaction resulted from severe crusting in S-S-S that reduced stand density and lowered yield for the chisel plow treatment. Wheat and alfalfa yields were not affected by tillage practice. Using average annual crop prices, the 5-year rotation generated returns that were 100 and 158% higher than for C-S using either no-tillage or chisel practices. This study confirms that producers who incorporate alfalfa into their crop rotations can significantly increase returns to land and management. However, returns for the rotation including alfalfa are more realistic where a viable forage market exists.

Rainfed Farming Systems in the USA

This chapter describes characteristics of four major rainfed farming regions and systems in the USA: Great Plains wheat-sorghum-cattle; midwestern corn-soybean-hogs, southern cotton-peanut-poultry, and coastal diversified crops-dairy. Rainfed farming systems in the USA are highly productive, economically important, ecologically diverse and technologically driven. Management approaches to achieve resource efficiency and agricultural sustainability are described, including the use of improved genetic seed sources, crop rotations, appropriate fertiliser application techniques, conservation tillage and integrated crop-livestock production systems. Issues of increasing oil and fertiliser prices, sustainability of soil and water resources, and climate change are current challenges facing agriculture in the USA.

Evaluation of Weed Control Strategies in Organic Soybean Production

A 2-year (2001 and 2002) organic soybean [Glycine max (L.) Merr.] study evaluated the contributions of row width (narrow 8-inch and wide 30-inch), mechanical weed control equipment (rotary hoe and cultivator), cultivation frequency (1 to 3 passes with one or both implements), and cultivation timing (early, late, or sequential) to annual broadleaf and grass weed control and grain yield. Narrow row (NR) systems reduced the timeframe available for cultivation compared to wide rows (WR) due to quicker canopy closure. A rotary hoe (RH) was equally or less effective in controlling weeds compared to a cultivator. Weed control was similar for early or late RH treatments, and early or late cultivator treatments. Yield did not differ among treatments in 2001. In 2002, the highest yields were achieved in WR with sequential 1 RH, 2 cultivator passes (54 bu/acre) compared to NR, 1 or 2 RH treatments (27 to 33 bu/acre). WR systems provide greater flexibility in cultivation equipment and timing, and may provide greater yield stability than NR systems.