Minnesota Soybean Research Articles

Relay‐Cropping Pennycress and Camelina with Soybean in Minnesota

Relay‐Cropping Pennycress and Camelina with Soybean in Minnesota

Economics and Agronomics of Relay‐Cropping Pennycress and Camelina with Soybean in Minnesota

Core Ideas Net income from relay cropping was rarely different from that of mono‐cropping. A 25‐cm oilseed row spacing was likely too narrow for optimal soybean growth. Further domestication of oilseeds will likely improve relay cropping with soybean. ABSTRACTCover crops can serve as a valuable management tool for improving soil and water quality, but are an added expense for farmers. We evaluated the yields and economics of four cover crops and two winter fallow treatments in a spring wheat (Triticum aestivum L.)–soybean [Glycine max (L.) Merr.] rotation at three sites in Minnesota. The four cover crop treatments were winter rye (Secale cereal L.), forage radish (Raphanus sativus L.), winter camelina [Camelina sativa (L.) Crantz], and pennycress (Thlaspi arvense L.) planted into spring wheat stubble. The fallow treatments consisted of no‐tilled and conventionally tilled soil. Radish winterkilled and rye was terminated chemically before planting soybean in early May. Soybean was inter‐seeded between rows of camelina and pennycress at the same time it was planted in other treatments. Camelina and pennycress were harvested over soybean seedlings in late June. Camelina yields ranged from 600 to 1100 kg ha−1, while pennycress ranged from 900 to 1550 kg ha−1. Mono‐cropped soybean averaged 1819, 3510, and 4180 kg ha−1 in northern, central, and southern Minnesota, respectively. Soybean seedlings under oilseed cover crop canopies exhibited light‐stress, which likely reduced soybean yield in these treatments by 22 to 30%. When oilseed and inter‐seeded soybean yields were combined, total seed yields generally were equal to or exceeded those of mono‐cropped soybean. In addition, net income for inter‐seeded systems was typically equivalent to mono‐cropped soybean. Improvements in net income are likely needed before the benefits of oilseed cover crops are fully realized.

Developing a growing degree day model for North Dakota and Northern Minnesota soybean

Farmers in North Dakota and Northern Minnesota did not have a model to predict when their soybean (Glycine max L. Merr.) crop will be mature. Soybean plants need to be mature before the first fall freeze. The objectives of this study were to estimate needed accumulated growing degree days (AGDD) for adapted soybean maturity groups (MG) to reach maturity (R8). Research was conducted during 2007–2012 at northern, central, and southern North Dakota, to develop a model to predict the soybean maturity date based on accumulated GDDs and to verify the model using field research data from 2013 to 2015. Based on 1816 data points a regression analysis was performed which predicted that 1666, 1862, 2030 AGDD (with a 50°F base temperature) were needed to reach maturity for 00.7, 0.4, and 1.0 MG soybean cultivars, respectively.The predicted values were used to create a model that allows producers to select the MG of their cultivar, date of planting, and the nearest North Dakota Agricultural Weather Network (NDAWN) station. The output provides the predicted maturity date, as well as the average first day of occurrence of select threshold temperatures (36°, 32° and 28°F) at 50% probability level. This model will help growers to judge the risks of certain frost occurring before the selected cultivar's projected maturity date. The projected maturity date is based on two parts. The first part is the observed period from the planting date to the date the model is queried and is based on daily maximum and minimum temperatures. The second part is the forecast period that is based on normal (1981–2010 average) daily maximum and minimum temperatures from the queried date through the end of the select growing season. The growing degree days (GDD) values are accumulated from the planting date through the end of season based on these daily maximum and minimum temperatures. Input into the model should be for adapted MG soybean for the region and for planting dates between May 15 and 31. Farmers and agriculturist in North Dakota and northwest Minnesota can use the model before planting to determine if a MG would mature before the frost with varying temperature thresholds and monitor the accumulation of GDD and development of the crop during the season and estimated date of maturity.

Spatial Patterns and Sequential Sampling Plans for Predators of Aphis glycines (Hemiptera: Aphididae) in Minnesota Soybean

The soybean aphid, Aphis glycines Matsumura, is an economically important soybean pest. Many studies have demonstrated that predatory insects are important in suppressing A. glycines population growth. However, to improve the utilization of predators in A. glycines management, sampling plans need to be developed and validated for predators. Aphid predators were sampled in soybean fields near Rosemount, Minnesota, from 2006-2007 and 2013-2015 with sample sizes of 20-80 plants. Sampling plans were developed for Orius insidiosus (Say), Harmonia axyridis (Pallas), and all aphidophagous Coccinellidae species combined. Taylor's power law parameters from the regression of log variance versus log mean suggested aggregated spatial patterns for immature and adult stages combined for O. insidiosus, H. axyridis, and Coccinellidae in soybean fields. Using the parameters from Taylor's power law and Green's method, sequential fixed-precision sampling plans were developed to estimate the density for each predator taxon at desired precision levels of 0.10 and 0.25. To achieve a desired precision of 0.10 and 0.25, the average sample number (ASN) ranged from 398-713 and 64-108 soybean plants, respectively, for all species. Resulting ASNs were relatively large and assumed impractical for most purposes; therefore, the desired precision levels were adjusted to determine the level of precision associated with a more practical ASN. Final analysis indicated an ASN of 38 soybean plants provided precision of 0.32-0.40 for the predators. Development of sampling plans should provide guidance for improved estimation of predator densities for A. glycines pest management programs and for research purposes.

Pythium, Phytophthora, and Phytopythium spp. Associated with Soybean in Minnesota, Their Relative Aggressiveness on Soybean and Corn, and Their Sensitivity to Seed Treatment Fungicides.

Pythium spp. cause seed decay, damping-off, and root rot in soybean and corn; however, their diversity and importance as pathogens in Minnesota are unknown. Our objectives were to identify the Pythium spp. present in Minnesota soybean fields, determine their aggressiveness on corn and soybean, and investigate their sensitivity to seed treatment fungicides. For identification, sequences obtained using internal transcribed space ITS4 and ITS1 primers were compared with reference sequences in the National Center for Biotechnology Information database. Seedling and soil samples yielded over 30 oomycete species. Aggressiveness was determined using two methods; a seed assay, which also examined temperature effects on aggressiveness, and a seedling assay. Of 21 species evaluated, seven Pythium spp. were pathogenic on both soybean and corn, reducing root growth by 20% or more while two Pythium and one Phytopythium spp. were pathogenic only on soybean. Aggressiveness of many isolates increased as temperature increased from 15°C to 25°C. The sensitivity of 10 pathogenic species to azoxystrobin, ethaboxam, mefenoxam, pyraclostrobin, or trifloxystrobin was tested. EC50 values for mefenoxam and ethaboxam were 10-2 of those to strobilurin fungicides. Pythium spp. in Minnesota are diverse and a significant cause of seedling disease on soybean and corn. Most Pythium spp. isolated in this study were more sensitive to mefenoxam and ethaboxam than to strobilurin fungicides.

Giant Ragweed (Ambrosia trifida) Seed Production and Retention in Soybean and Field Margins

As herbicide-resistant weed populations become increasingly problematic in crop production, alternative strategies of weed control are necessary. Giant ragweed, one of the most competitive agricultural weeds in row crops, has evolved resistance to multiple herbicide biochemical sites of action within the plant, necessitating the development of new and integrated methods of weed control. This study assessed the quantity and duration of seed retention of giant ragweed grown in soybean fields and adjacent field margins. Seed retention of giant ragweed was monitored weekly during the 2012 to 2014 harvest seasons using seed collection traps. Giant ragweed plants produced an average of 1,818 seeds per plant, with 66% being potentially viable. Giant ragweed on average began shattering hard (potentially viable) and soft (nonviable) seeds September 12 and continued through October at an average rate of 0.75 and 0.44% of total seeds per day during September and October, respectively. Giant ragweed seeds remained on the plants well into the Minnesota soybean harvest season, with an average of 80% of the total seeds being retained on October 11, when Minnesota soybean harvest was approximately 75% completed in the years of the study. These results suggest that there is a sufficient amount of time to remove escaped giant ragweed from production fields and field margins before the seeds shatter by managing weed seed dispersal before or at crop harvest. Controlling weed seed dispersal has potential to manage herbicide-resistant giant ragweed by limiting replenishment of the weed seed bank.

Efficacy of Foliar Insecticides for Management of Grape Colaspis, 2015: Table 1

This study aimed to evaluate insecticides for management of adults of the grape colaspis in Minnesota soybean. The study was conducted at the University of Minnesota Research, Outreach and Education Park near Rosemount, Minnesota. On 24 Jun 2015, soybean seeds (variety: P19T01R) were sown 3.81 cm deep at a seeding rate of 508,970 seeds/ha. The spacing between rows was 17 cm. Plots were arranged in a randomized complete block design with five replications of three treatments (Table 1). Plots were 3.05 m wide by 9.14 m long …

Association mapping and genomic prediction for resistance to sudden death syndrome in early maturing soybean germplasm.

Sudden death syndrome (SDS), caused by Fusarium virguliforme, has spread to northern soybean growing regions in the US causing significant yield losses. The objectives of this study were to identify loci underlying variation in plant responses to SDS through association mapping (AM) and to assess prediction accuracy of genomic selection (GS) in a panel of early maturing soybean germplasm. A set of 282 soybean breeding lines was selected from the University of Minnesota soybean breeding program and then genotyped using a genome-wide panel of 1536 single-nucleotide polymorphism markers. Four resistance traits, root lesion severity (RLS), foliar symptom severity (FSS), root retention (RR), and dry matter reduction (DMR), were evaluated using soil inoculation in the greenhouse. AM identified significant peaks in genomic regions of known SDS resistance quantitative trait loci cqSDS001, cqRfs4, and SDS11-2. Additionally, two novel loci, one on chromosome 3 and another on chromosome 18, were tentatively identified. A ninefold cross-validation scheme was used to assess the prediction accuracy of GS for SDS resistance. The prediction accuracy of single-trait GS (ST-GS) was 0.64 for RLS, but less than 0.30 for RR, DMR, and FSS. Compared to ST-GS, none of multi-trait GS (MT-GS) models significantly improved the prediction accuracy due to weak correlations between the four traits. This study suggests both AM and GS hold promise for implementation in genetic improvement of SDS resistance in existing soybean breeding programs.Electronic supplementary materialThe online version of this article (doi:10.1007/s11032-015-0324-3) contains supplementary material, which is available to authorized users.

Field Pennycress Production and Weed Control in a Double Crop System with Soybean in Minnesota

Sustainable intensification of agricultural systems has been suggested as a way to increase food, fiber, energy, and feed to meet future demands. Field pennycress (Thlaspi arvense L.) is proposed as a means for temporal intensification of agriculture, increasing profitability through oilseed production while providing needed cover to address soil and water quality issues. Field research was conducted across four environments in Minnesota to (i) evaluate pennycress planting date and seeding rate on pennycress and soybean [Glycine max (L.) Merr.] seed production and (ii) determine the role of pennycress systems as a weed management tool. Pennycress seeding rate had a direct effect on pennycress yield at Rosemount but not at Waseca or Lamberton locations. The use of a companion cover crop along with pennycress further reduced pennycress seed yield at Rosemount, but not Waseca or Lamberton suggesting that water availability is a key driver in pennycress productivity. The effect of pennycress and cover crops on soybean yield was also dependent on location. At Rosemount, soybean yield was reduced when pennycress was planted ahead of soybeans both years of the study while there was no effect of pennycress on soybean yield at Waseca. Although soybean yield was reduced at Rosemount, the combined pennycress and soybean seed yield was greater. This research shows the potential for a double cropping system of pennycress–soybean to increase overall seed yield and reduce early‐season weed pressure.

Potential of Association Mapping and Genomic Selection to Explore PI 88788 Derived Soybean Cyst Nematode Resistance

The potential of association mapping (AM) and genomic selection (GS) has not yet been explored for investigating resistance to soybean cyst nematode (SCN), the most destructive pest affecting soybean. We genotyped 282 representative accessions from the University of Minnesota soybean breeding program using a genome‐wide panel of 1536 single nucleotide polymorphism (SNP) markers and evaluated plant responses to SCN HG type 0. After adjusting for population structure, AM detected significant signals at two loci corresponding to rhg1 and FGAM1 plus a third locus located at the opposite end of chromosome 18. Our analysis also identified a discontinuous long‐range haplotype of over 600 kb around rhg1 locus associated with resistance to SCN HG type 0. The same phenotypic and genotypic datasets were then used to access GS accuracy for prediction of SCN resistance in the presence of major genes through a sixfold cross‐validation study. Genomic selection using the full marker set produced average prediction accuracy ranging from 0.59 to 0.67 for SCN resistance, significantly more accurate than marker‐assisted selection (MAS) strategies using two rhg1‐associated DNA makers. Reducing the number of markers to 288 SNPs in the GS training population had little effect on genomic prediction accuracy. This study demonstrates that AM can be an effective genomic tool for identifying genes of interest in diverse germplasm. The results also indicate that improved MAS and GS can enhance breeding efficiency for SCN resistance in existing soybean improvement programs.

Species composition, abundance, and seasonal dynamics of stink bugs (Hemiptera: Pentatomidae) in Minnesota soybean fields.

Stink bugs (Hemiptera: Pentatomidae) have historically not been pests of soybean in Minnesota. In response to the invasion of Halyomorpha halys (Stål) and reports of increasing abundance of species native to North America, a state-wide survey of soybean was conducted over 3 yr in Minnesota to determine species composition, abundance, and seasonal dynamics of Pentatomidae associated with soybean. Fourteen species of Pentatomidae (12 herbivorous and two predatory) were collected from soybean. H. halys was not detected in this survey. Among the herbivorous species found, adults of Euschistus variolarius (Palisot de Beauvois) had the greatest relative abundance (60.51%) and frequency of detection (18.44%), followed by Euschistus servus euschistoides (Say) (19.37 and 3.04%, respectively) and Chinavia hilaris (Say) (5.50 and 1.69%, respectively). Abundance of herbivorous nymphs and adults exceeded an economic threshold (20 nymphs and adults per 100 sweeps) in 0.82% of fields in 2012 but not in 2011 or 2013. The frequency of detection of herbivorous species and ratio of nymphs to adults increased with increasing reproductive growth stage of soybean. In two of three years, herbivorous adults were more abundant in the edge compared with interior of fields. Two predatory Pentatomidae, Podisus maculiventris (Say) and Podisus placidus Uhler, comprised 5.95 and 1.62% of the pentatomid adults. Though the species composition of Pentatomidae in Minnesota soybean differs from that in eastern and southern states, the spatial (i.e., greater abundance near field edge) and seasonal dynamics (i.e., increasing abundance and reproduction with increasing reproductive maturity of soybean) in soybean appear similar.

Response of Soybean Insects to an Autumn-Seeded Rye Cover Crop

We evaluated the hypothesis that the use of an autumn-seeded winter rye, Secale cereale L., cover crop in soybean, Glycine max (L.) Merr., could lead to decreased insect pest pressure. We compared insect pest and natural enemy populations in an organic soybean production system with soybeans planted into an autumn-seeded rye cover crop (i.e., soybeans planted in spring into a rye cover crop that had been planted the previous autumn). Small-plot experiments were conducted at two locations in southwestern Minnesota to compare insect populations on soybean planted into fallow ground versus soybean planted into rye that was managed by mowing using three different techniques. Densities of potato leafhopper, Empoasca fabae (Harris), were significantly lower on soybean in all of the rye treatments compared with soybean without rye at both locations. Densities of soybean aphid, Aphis glycines Matsumura, were significantly lower on all of the treatments incorporating rye than the soybean-only treatment at one site, but the suppressive effect of rye depended on the specifics of rye planting at the other site. Densities of bean leaf beetle, Cerotoma trifurcata (Förster), were significantly lower in the rye plots than soybean-only plots at one of the two sites. Foliar-foraging insect predator densities did not differ significantly among treatments at either site. Soybean yields did not differ significantly among treatments at either location although there was a trend for lower yield in two of the rye treatments. A statewide survey also was conducted to compare A. glycines infestations in Minnesota soybean fields with and without a rye cover crop. The proportion of plants infested and infestation ratings were both significantly lower in soybean fields with rye than in those without.

First Report of Fusarium redolens Causing Root Rot of Soybean in Minnesota.

Multiple Fusarium species have been found in association with soybean (Glycine max) plants exhibiting root rot in the United States (3). Soybean plants that lacked apparent foliar symptoms, but exhibited 2- to 5-mm brown, necrotic taproot lesions and lateral root necrosis were observed in Minnesota in one field each in Marshall and Otter Tail counties in July of 2007, as well as in one field in Marshall County in July of 2008. Sampling was conducted as part of a study investigating root rot in major soybean-production areas of Minnesota. Plants were arbitrarily dug up at the R3 growth stage. Root systems were washed, surface disinfested in 0.5% NaOCl for 3 min, rinsed in deionized water, and dried. Fusarium isolates were recovered from root sections with necrotic lesions embedded in modified Nash-Snyder medium (1). One resulting Fusarium colony from one plant per county was transferred to half-strength acidified potato dextrose agar (PDA) and carnation leaf agar (CLA) to examine morphological characteristics (4). Culture morphology on PDA consisted of flat mycelium with sparse white aerial mycelium. On CLA, thick-walled macroconidia with a hooked apical cell and a foot-shaped basal cell were produced in cream-colored sporodochia. Macroconidia ranged from 32.5 to 45.0 μm long. Microconidia were oval to cylindrical with 0 to 1 septa, ranged from 7.5 to 11.25 μm long, and were produced on monophialides. Chlamydospores were produced abundantly in chains that were terminal and intercalary in the hyphae of 4-week-old cultures. Morphological characteristics of the three isolates were consistent with descriptions of F. redolens (2,4). The identity of each isolate was confirmed by sequencing the translation elongation factor 1-α (TEF) locus (4). BLAST analysis of the TEF sequences from each isolate against the FUSARIUM-ID database resulted in a 100% match for 17 accessions of F. redolens (e.g., FD 01103, FD 01369). Each F. redolens isolate was tested for pathogenicity on soybean. Sterile sorghum grain was infested with each isolate and incubated for 2 weeks. Sterile sorghum was used for control plants. Soybean seeds of cv. AG2107 were planted in 11.4-cm pots ~1 cm above a 25-cm3 layer of infested sorghum or sterile sorghum. Two replicate pots containing four plants each were used per treatment and the experiment was repeated once. Root rot was assessed 28 days after planting. Each F. redolens isolate consistently caused taproot necrosis on inoculated plants, whereas control plants did not exhibit root necrosis. Isolations were made from roots of inoculated and control plants and the isolates recovered from inoculated plants were identified as F. redolens based on morphological characteristics and TEF sequences. Fusarium species were not isolated from control plants. To our knowledge, this is the first report of F. redolens causing root rot of soybean; however, it is possible F. redolens has been found previously and misidentified as F. oxysporum (2,4). Results from inoculations suggest that F. redolens may be an important root rot pathogen in Minnesota soybean fields.

Year, Region, and Temperature Effects on the Quality of Minnesota's Soybean Crop

Bulk commodity soybean [Glycine max (L.) Merr.] can now be sourced with great specificity through rail and container purchases. The objective of this study was to determine whether analyses of farmer‐grown soybean seed samples could detect significant regional differences in soybean quality traits. Through analysis of 2706 farmer volunteered soybean samples representing harvests from 2003–2005, we found significant year and region effects on seed quality. An independent variable, temperature during seed filling (Tsf) was created for each soybean sample by kriging local daily mean air temperatures from 135 weather stations. A region × year interaction was noted for protein and the sum of protein and oil concentrations, but using Tsf as a covariate eliminated this interaction. The variable Tsf correlated with average regional oil concentrations such that oil concentration increased at a rate of 6.6 g kg−1 °C−1. Overall, farmer produced and volunteered soybean samples provide an excellent means of identifying within‐state soybean seed quality variation. Additionally, local climate data (Tsf) can be used to predict this variation in regional soybean seed quality.

Interactions between iron-deficiency chlorosis and soybean cyst nematode in Minnesota soybean fields

Experiments were conducted in four commercial fields differing in severity of iron-deficiency chlorosis (IDC), and soybean cyst nematode (SCN) in Waseca and Lamberton, Minnesota to determine the interaction between the IDC and SCN. Each experiment was a randomized complete block with a factorial treatment design including 23 cultivars with or without traits of resistance to SCN, and IDC. The study illustrated the interactive effects of the two defensive traits on the diseases and soybean yields. IDC rating was higher in SCN-susceptible than SCN-resistant soybean, suggesting SCN infection increased IDC. Resistance to IDC apparently increased SCN reproduction due to better soybean plant growth. Yield response to the defensive traits depended on the disease pressures in a field. When both IDC and SCN were present in a field, deploying SCN-resistance was the best solution to the problems. However, SCN-resistance suppressed soybean yields when used in fields without the disease problems. IDC-resistance increased yield of SCN-susceptible cultivars, but it did not result in detectable yield benefit of SCN-resistant cultivars in SCN-infested sites. Effective use of the defensive traits for management of IDC and SCN requires specific knowledge of the disease problems present in a field.

Efficacy of Thiamethoxam to Suppress Soybean Aphid Populations in Minnesota Soybean

Soybean aphid poses a serious threat to soybean production in the United States and Canada by reducing plant height, pod number, and yield. Since its introduction, foliar insecticides have been the most common method to control soybean aphid. Treatment of soybean seed with a systemic insecticide may provide producers with an alternative to foliar applied insecticides. Therefore, our objective was to evaluate the efficacy of a seed treatment to suppress soybean aphid populations in soybean. In 2003, 2004, and 2005 we conducted field studies and supportive laboratory and in-field bioassays (2003 and 2004 only for bioassays) to assess mortality under controlled conditions. In the field, soybean aphid populations were assessed weekly by counting the total number of aphids per plant. In an excised-leaf bioassay, aphid mortality persisted 23 to 35 days after planting. In an in-field bioassay (2004 only), intact plants showed longer persistence of thiomethoxam and aphid mortality persisted 49 days after planting and mortality was significantly higher in the older leaves than in newly-expanded leaves. In all years and under various aphid densities, thiamethoxam significantly reduced season-long aphid pressure by 45.0 to 66.7%. However, thiamethoxam treatment did not significantly increase yield in three of four location-years, which coincided with low aphid density in untreated control plots.

Registration of ‘MN1302’ Soybean

Crop ScienceVolume 44, Issue 2 p. 693-693 Registration of Cultivar Registration of ‘MN1302’ Soybean J.H. Orf, Corresponding Author J.H. Orf orfxx001@umn.edu Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN, 55108Corresponding author (orfxx001@umn.edu)Search for more papers by this authorR.L. Denny, R.L. Denny Dep. of Plant Pathology, Univ. of Minnesota, St. Paul, MN, 55108Search for more papers by this author J.H. Orf, Corresponding Author J.H. Orf orfxx001@umn.edu Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN, 55108Corresponding author (orfxx001@umn.edu)Search for more papers by this authorR.L. Denny, R.L. Denny Dep. of Plant Pathology, Univ. of Minnesota, St. Paul, MN, 55108Search for more papers by this author First published: 01 March 2004 https://doi.org/10.2135/cropsci2004.6930Citations: 9 Work supported in part by grants from the Minnesota Soybean Research and Promotion Council. Contribution from the Minnesota Agric. Exp. Stn. Registration by CSSA. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume44, Issue2March–April 2004Pages 693-693 RelatedInformation

Registration of ‘MN0302’ Soybean

Crop ScienceVolume 44, Issue 2 p. 692-693 Registration of Cultivar Registration of ‘MN0302’ Soybean J.H. Orf, Corresponding Author J.H. Orf orfxx001@umn.edu Dep. of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN, 55108Corresponding author. (orfxx001@umn.edu)Search for more papers by this authorR.L. Denny, R.L. Denny Dep. of Plant Pathology, University of Minnesota, St. Paul, MN, 55108Search for more papers by this author J.H. Orf, Corresponding Author J.H. Orf orfxx001@umn.edu Dep. of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN, 55108Corresponding author. (orfxx001@umn.edu)Search for more papers by this authorR.L. Denny, R.L. Denny Dep. of Plant Pathology, University of Minnesota, St. Paul, MN, 55108Search for more papers by this author First published: 01 March 2004 https://doi.org/10.2135/cropsci2004.6920Citations: 1 Work supported in part by grants from the Minnesota Soybean Res. and Promotion Council. Contribution from the Minnesota Agric. Exp. Stn. Registration by CSSA. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume44, Issue2March–April 2004Pages 692-693 RelatedInformation

First Report of Charcoal Rot (Macrophomina phaseolina) on Soybean in Minnesota.

In August 1999, soybean (Glycine max (L.) Merr.) plants exhibiting symptoms of charcoal rot were observed near Zumbrota, MN. Symptoms included shrunken, unfilled pods, and brown, wilted leaves attached to dead petioles and stems (1). When stems of symptomatic soybean plants were split, areas of gray-to-black discoloration where present in the stem cortex (1). Black, spherical microsclerotia 77 to 90 µm in diameter and elongated microsclerotia 77 to 120 µm long (1) were found in vascular tissue. Stem tissue placed on potato dextrose agar (PDA) yielded fungal colonies identified as Macrophomina phaseolina (Tassi) Goid. based on gray colony color, colony morphology, and the presence of microsclerotia 70 to 90 µm in diameter. In 2000, M. phaseolina was isolated from plant samples gathered from 11 of 90 fields sampled in a statewide soybean disease survey. More studies are needed to determine the distribution of charcoal rot in Minnesota; however, the occurrence of symptoms at one location and the presence of M. phaseolina in soybean-growing areas of Minnesota suggest that charcoal rot may occur in susceptible soybean cultivars under favorable environmental conditions. Reference: (1) G. S. Smith and T. D. Wyllie. Charcoal rot. Pages 29-30 in: Compendium of Soybean Diseases, 4th ed. G. L. Hartmann, J. B. Sinclair, and J. C. Rupe, eds. The American Phytopathological Society, St. Paul, MN, 1999.

In‐Season Fertilizer Nitrogen Applications for Soybean in Minnesota

Predicted physiological factors and a limited number of field studies have resulted in debate regarding the recommendation of in‐season fertilizer N for soybean [Glycine max. (L.) Merrill]. The objective of our research was to evaluate several in‐season N fertilization strategies on soybean seed yield response as well as to measure the effect of fertilizer N additions on late‐season plant N concentrations and accumulation, seed N removal, seed protein, and seed oil composition. The research was conducted at 12 sites in the southern soybean‐growing region of Minnesota in 1998 and 1999. A combination of (i) application time (July vs. August), (ii) placement method (broadcast vs. knifed), and (iii) N source (urea vs. poly‐coated urea) gave five N treatments plus a control at all sites. Seed yield did not respond to the fertilizer N treatments at any of the 12 sites; however, a combined analysis indicated a significant increase (generally less than 0.06 Mg ha−1) from using polymer‐coated urea or applying the urea in August. Herbage dry matter (DM) and herbage N concentrations at the R6 stage were not affected by any of the N fertilizer strategies. Although soybean seed protein was statistically different among the treatments, protein was only increased 0.4 g kg−1. Soybean oil concentration was not affected by fertilizer treatments. In general, polymer‐coated urea, knifed applications, and August applications increased soil NO3–N in the 0‐ to 30‐cm layer at R6 relative to standard urea, broadcast applications, and July applications. Even though in‐season N fertilizer created greater levels of available soil N at all 12 sites during soybean pod filling, seed yield was not improved compared with unfertilized control plots at any site. As a result, the University of Minnesota does not recommended in‐season N fertilizer applications for soybean production.