Randall L. Smoot

Winter-Annual Weed Management in Corn (Zea mays) and Soybean (Glycine max) and the Impact on Soybean Cyst Nematode (Heterodera glycines) Egg Population Densities'

Field research was conducted at Columbia and Novelty, MO, to determine the impact of winter-annual weed management systems on corn and soybean grain yields, winter-annual weed control, and soybean cyst nematode (SCN) egg population densities over the crop production cycle. Corn grain yield was not affected by winter-annual weed management systems. Soybean grain yield was not affected by winter weed management systems in 2001, but at Columbia in 2002 winter rye and Italian ryegrass reduced soybean grain yield 62 and 64%, respectively. Fall-applied simazine + tribenuron in corn and chlorimuron + sulfentrazone in soybean controlled winter-annual weeds greater than 99%. Fall-overseeded winter rye and Italian ryegrass in corn and overseeded Italian ryegrass in soybean controlled winter weeds 66 to 86%. In the soybean studies, race 4 SCN population densities increased (P  =  0.08) in the nontreated control and remained stable (P  =  0.55) with fall-applied chlorimuron + sulfentrazone from fall 2001 to spring 2002 while SCN population densities were reduced (P  =  0.06) with spring-applied chlorimuron + sulfentrazone from fall 2002 to spring 2003. In the corn studies, none of the winter-annual weed management strategies reduced (P > 0.22) race 2 SCN population densities except winter rye from fall 2001 to spring 2002 (P  =  0.05). This research indicates that control of weed species considered to be weak alternative hosts for SCN affected SCN population densities some instances when race 4 SCN population densities were high in a continuous soybean production system or race 2 SCN population densities were low in a 2-yr corn production system. Nomenclature: Chlorimuron, sulfentrazone, simazine, tribenuron, common chickweed, Stellaria media (L.) Vill. #3 STEME, field pennycress, Thlaspi arvense L. # THLAR, henbit, Lamium amplexicaule L. # LAMAM, soybean cyst nematode, Heterodera glycines Ichinohe, corn, Zea mays L. ‘Asgrow RX740 RR’, Italian ryegrass, Lolium multiflorum L. ‘Marshall’, soybean, Glycine max (L.) Merr. ‘DK 38-52’, winter rye, Secale cereale L. ‘Forage Master’. Additional index words: Weed–nematode interaction, integrated pest management. Abbreviations: COC, crop oil concentrate.

Corn Hybrid Response to Water Management Practices on Claypan Soil

A study evaluated corn (Zea mays L.) hybrids (Asgrow785, DKC61-73, DKC63-42, LG2642, and Kruger2114) and water management systems (nondrained, nonirrigated (NDNI); drained, nonirrigated (DNI) with subsurface drain tiles 6.1 and 12.2 m apart; drained plus subirrigated (DSI) with tiles 6.1 and 12.2 m apart; nondrained, overhead irrigated (NDOHI)) on yields, plant population, and grain quality from 2008 to 2010. Precipitation during this study was 36 to 283 mm above the past decade. Planting date was delayed 18 d in the nondrained control in 2009, and additional delayed planting controls were included this year. Grain yields were similar in the 6.1- and 12.2 m-spaced DNI and DSI systems in 2008 and 2010, but plant population increased 74% and yields were 3.1 Mg ha−1 greater with DSI at a 6.1 m spacing compared to 12.2 m in 2009. At a 6.1 m spacing, DNI or DSI increased yield 1.1 to 6.6 Mg ha−1 (10 to over 50%) compared to NDNI or NDOHI soil. High yielding hybrids achieved similar yields with DNI, while NDNI DKC63-42 had 1.2 Mg ha−1 greater yields compared to DKC61-73. A 6.1 m spacing for DNI claypan soils is recommended for high yielding corn production.

Yellow Nutsedge (Cyperus esculentus) Interference in Soybean

Abstract Field research was conducted in 2000 and 2001 to determine the effect of yellow nutsedge emergence timing and plant density on soybean yield and on yellow nutsedge propagation the following year. Yellow nutsedge tubers were planted at 0-, 7.5- (13/m2), 15- (8.6/m2), 30- (4.3/m2), 60- (2.2/m2), and 90-cm (1.5/m2) in-row spacings with soybean. Yellow nutsedge densities from 2.2 to 13 plants/m2 in a high-yield year (2000) and 4.3 to 13 plants/m2 in a low-yield year (2001) reduced grain yields 9 to 34%. In a separate experiment, tubers were planted 0, 2, 4, 6, and 8 wk after planting at a 15-cm (8.6/m2) in-row spacing. Seedlings that emerged with the crop and until 2 wk after planting reduced yield 9 to 11%. Yellow nutsedge densities from 1.5 to 13 plants/m2 contributed to significant aboveground biomass production, even with a competitive crop, such as soybean. For every gram of aboveground yellow nutsedge biomass produced in the fall, there were more than four shoots present the following spring. Nomenclature: Yellow nutsedge, Cyperus esculentus L. CYPES; soybean, Glycine max (L.) Merr. ‘Asgrow 3701’

Wheat (Triticum aestivum L.) cultivar selection affects double-crop and relay-intercrop soybean (Glycine max L.) response on claypan soils.

Field research (2003–2005) evaluated the effect of wheat row spacing (19 and 38 cm) and cultivar on double-cropped (DC) soybean response, 38-cm wheat on relay-intercrop (RI) response, and wheat cultivar selection on gross margins of these cropping systems. Narrow-row wheat increased grain yield 460 kg h a − 1 , light interception (LI) 7%, and leaf area index (LAI) 0.5 compared to wide rows, but did not affect DC soybean yield. High yielding wheat (P25R37) with greater LI and LAI produced lower (330 kg  h a − 1 ) soybean yields in an RI system than a low yielding cultivar (Ernie). Gross margins were

Spring-Interseeded Winter Rye Seeding Rates Influence Weed Control and Organic Soybean Yield

267  h a − 1 greater when P25R37 was RI with H431 Intellicoat (ITC) soybean compared to Ernie. Gross margins were similar for monocrop H431 non-coated (NC) or ITC soybean, P25R37 in 19- or 38-cm rows with DC H431 NC soybean, and P25R37 in 38-cm rows with RI H431 ITC soybean in the absence of an early fall frost.

Utility of Dried Distillers Grain as a Fertilizer Source for Corn

Field research in 2002 and 2003 evaluated spring-interseeded winter rye (Secale cereale L.) at 67, 134, or 200 kg ha−1 at two soybean (Glycine max (L.) Merr.) row spacings (19- and 76-cm) on weed control, yield, and gross margins. Based on regression analysis, wide-row (76-cm) soybean grain yield and gross margins were greatest when winter rye was interseeded at 114 and 106 kg ha−1, respectively. Yields and gross margins for wide-row soybean were 8 to 55% greater than narrow-row (19-cm) soybean seeded at 494,000 or 742,000 seeds ha−1 which was probably due to flexibility for implementing cultivation. As interseeded rye rates increased from 67 to 200 kg ha−1, yields and gross margins for narrow-rows decreased. Soybean row spacing had minimal impacts on specific weed species and total weed biomass or density. The use of wide-row soybean and spring-interseeded rye at 67 kg ha−1 was more cost-effective compared to narrow rows.