Integrated Effects of Genetic Resistance and Prothioconazole + Tebuconazole Application Timing on Fusarium Head Blight in Wheat.

Integrated Fusarium head blight (FHB) management programs consisting of different combinations of cultivar resistance class and an application of the fungicide prothioconazole + tebuconazole at or after 50% early anthesis were evaluated for efficacy against FHB incidence (INC; percentage of diseased spikes), index (IND; percentage of diseased spikelets per spike), Fusarium damaged kernel (FDK), deoxynivalenol (DON) toxin contamination, grain yield, and test weight (TW) in inoculated field trials conducted in 11 U.S. states in 2014 and 2015. Mean log response ratios and corresponding percent control values for INC, IND, FDK, and DON, and mean differences in yield and TW relative to a nontreated, inoculated susceptible check (S_CK), were estimated through network meta-analyses as measures of efficacy. Results from the analyses were then used to estimate the economic benefit of each management program for a range of grain prices and fungicide applications costs. Management programs consisting of a moderately resistant (MR) cultivar treated with the fungicide were the most efficacious, reducing INC by 60 to 69%, IND by 71 to 76%, FDK by 66 to 72%, and DON by 60 to 64% relative to S_CK, compared with 56 to 62% for INC, 68 to 72% for IND, 66 to 68% for FDK, and 58 to 61% for DON for programs with a moderately susceptible (MS) cultivar. The least efficacious programs were those with a fungicide application to a susceptible (S) cultivar, with less than a 45% reduction of INC, IND, FDK, or DON. All programs were more efficacious under conditions favorable for FHB compared with less favorable conditions, with applications made at 50% early anthesis being of comparable efficacy to those made 2 to 7 days later. Programs with an MS cultivar resulted in the highest mean yield increases relative to S_CK (541 to 753 kg/ha), followed by programs with an S cultivar (386 to 498 kg/ha) and programs with an MR cultivar (250 to 337 kg/ha). Integrated management programs with an MS or MR cultivar treated with the fungicide at or after 50% early anthesis were the most likely to result in a 50 or 75% control of IND, FDK, or DON in a future trial. At a fixed fungicide application cost, these programs were $4 to $319/MT more economically beneficial than corresponding fungicide-only programs, depending on the cultivar and grain price. These findings demonstrate the benefits of combining genetic resistance with a prothioconazole + tebuconazole treatment to manage FHB, even if that treatment is applied a few days after 50% early anthesis.

Interruption of the transmission of Onchocerca volvulus in the Kashoya-Kitomi focus, western Uganda by long-term ivermectin treatment and elimination of the vector Simulium neavei by larviciding.

Uganda is the only country in sub-Saharan Africa whose onchocerciasis elimination programme extensively uses vector control and biannual treatment with ivermectin. The purpose of this study was to assess the impact of combined strategies on interrupting onchocerciasis transmission in the Kashoya-Kitomi focus. Mass Drug Administration annually (13 years) followed by biannual treatments (6 years) and ground larviciding (36 cycles in 3 years) with temephos (Abate®, EC500) against Simulium neavei were conducted. Routine fly catches were conducted for over seven years in six catching sites and freshwater crabs Potamonautes aloysiisabaudiae were examined for immature stages of Simulium neavei. Epidemiological assessments by skin snip were performed in 2004 and 2013. Collection of dry blood spots (DBS) from children <10 years for IgG4 antibodies analysis were done in 2010 and 2013. Treatment coverage with ivermectin improved with introduction of biannual treatment strategy. Microfilaria prevalence reduced from 85% in 1991 to 62% in 2004; and to only 0.5% in 2013. Crab infestation reduced from 59% in 2007 to 0% in 2013 following ground larviciding. Comparison of total fly catches before and after ground larviciding revealed a drop from 5334 flies in 2007 to 0 flies in 2009. Serological assays conducted among 1,362 children in 2010 revealed 11 positive cases (0.8%; 95% CI: 0.4%-1.2%). However, assessment conducted on 3246 children in 2013 revealed five positives, giving point prevalence of 0.15%; 95% CI: 0.02%-0.28%. Four of the five children subjected to O-150 PCR proved negative. The data show that transmission of onchocerciasis has been interrupted based on national and WHO Guidelines of 2012 and 2016, respectively.

Determination of Heterodera glycines Virulence Phenotypes Occurring in South Dakota.

The soybean cyst nematode (SCN), Heterodera glycines, is the most important yield-limiting pathogen of soybean in the United States. In South Dakota, SCN has been found in 29 counties, as of 2016, and continues to spread. Determining the virulence phenotypes (HG types) of the SCN populations can reveal the diversity of the SCN populations and the sources of resistance that would be most effective for SCN management. To determine the HG types prevalent in South Dakota, 250 soil samples were collected from at least three arbitrarily selected fields in each of the 28 counties with fields previously found to be infested with SCN. SCN was detected in 82 fields (33%), and combined egg and juvenile counts ranged from 200 to 65,200 per 100 cm3 of soil. Eggs and juveniles were extracted from each soil sample and were used to infest seven SCN HG type test indicator soybean lines and 'Williams 82' as the susceptible check. A female index (FI) was calculated based on the number of females found on each indicator line relative to those on the susceptible check. A FI equal to or greater than 10% in any line was assigned as that HG type. Out of 73 SCN populations for which HG type tests were done, 63% had FI ≥10% on PI 548316 (indicator line #7), 25% on PI 88788 (#2), 19% on PI 209332 (#5), 7% on PI 548402 (#1), 4% on PI 90736 (#3), and 4% on PI 89722 (#6). None of the SCN populations had FI ≥10% on PI 437654 (indicator line #4). The most prevalent HG types were 0, 2.5.7, and 7. These accounted for 81% of all the HG types determined for the samples tested. HG types with ≥10% reproduction on indicator lines PI 88788, PI 209332, and PI 548317 were most prevalent in the soil samples tested, suggesting that the use of these sources of resistance for developing SCN resistant cultivars should be avoided. For sustainable SCN management, use of resistant cultivars should be rotated with nonhost crops and cultivars with different sources of resistance.

Incidence of Wheat streak mosaic virus, Triticum mosaic virus, and Wheat mosaic virus in Wheat Curl Mites Recovered from Maturing Winter Wheat Spikes.

Wheat curl mites (WCM; Aceria tosichella) transmit Wheat streak mosaic virus (WSMV), Triticum mosaic virus (TriMV), and Wheat mosaic virus (WMoV) to wheat (Triticum aestivum L.) in the Great Plains region of the United States. These viruses can be detected in single, double, or triple combinations in leaf samples. Information on incidence of viruses in WCM at the end of the growing season is scant. The availability of this information can enhance our knowledge of the epidemiology of WCM-transmitted viruses. This research was conducted to determine the frequency of occurrence of WSMV, TriMV, and WMoV in WCM populations on field-collected maturing wheat spikes and to determine differences in WCM densities in three geographical regions (southeast, west-central, and panhandle) in Nebraska. Maturing wheat spikes were collected from 83 fields across Nebraska in 2011 and 2012. The spikes were placed in proximity to wheat seedlings (three- to four-leaf stage) in WCM-proof cages in a growth chamber and on sticky tape. WCM that moved off the drying wheat spikes in cages infested the wheat seedlings. WCM that moved off wheat spikes placed on sticky tape were trapped on the tape and were counted under a dissecting microscope. At 28 days after infestation, the wheat plants were tested for the presence of WSMV, TriMV, or WMoV using enzyme-linked immunosorbent assay and multiplex polymerase chain reaction. WSMV was the most predominant virus detected in wheat seedlings infested with WCM from field-collected spikes. Double (TriMV+WSMV or WMoV+WSMV) or triple (TriMV+ WMoV +WSMV) virus detections were more frequent (47%) than single detections (5%) of TriMV or WSMV. Overall, 81% of the wheat seedlings infested with WCM tested positive for at least one virus. No significant association (P > 0.05) was found between regions for WCM trapped on tape. These results suggest that WCM present on mature wheat spikes harbor multiple wheat viruses and may explain high virus incidence when direct movement of WCM into emerging winter wheat occurs in the fall.

Bean pod mottle virus Time of Infection Influences Soybean Yield, Yield Components, and Quality.

Bean pod mottle virus (BPMV) negatively affects soybean yield and quality, yet quantitative information on effect of time of BPMV infection on soybean yield and quality has not been reported. The impact of time of BPMV infection on soybean yield, yield components, and grain quality components were quantified during the 2006 and 2007 soybean growing seasons in Iowa. Soybean quadrats (30 cm in length) were established within soybean plots ('NB3001') that consisted of six rows and were 7.5 m long. Quadrats were sampled 9 times during the 2006 growing season and 10 times during the 2007 growing season, beginning 25 days after planting in both years. Sap was extracted from leaflet samples from each quadrat and tested for the presence or absence of BPMV by enzyme-linked immunosorbent assay. The day of year (DOY) and quadrat position when BPMV was first detected within each plot were recorded and mapped. Soybean yield, number of pods per plant, number of seed per pod, and 100-seed weight for each quadrat were determined. The relationship between time (DOY) of BPMV infection and soybean yield, soybean yield components, and soybean grain quality were then quantified using linear regression. DOY of BPMV infection within quadrats explained 89.7 and 57.9% of the variation in soybean grain yield in 2006 and 2007, respectively. Soybean yield damage functions (slopes) were 15.2 and 8.1 kg/ha per day, respectively, indicating that, for each day that BPMV infection was delayed, soybean yield increased by 15.2 kg/ha in 2006 and 8.1 kg/ha in 2007. The number of pods per plant increased by 0.15 pods for each day that BPMV infection was delayed (R2 = 72.8%) in 2006 but there was no relationship in 2007. The 100-seed weight had a significant linear relationship with the DOY when BPMV was first detected within quadrats in 2006 (slope = 0.013, R2 = 86.3%) but not in 2007. The percentage of mottled seed in 2006 decreased by 1% for each day that BPMV infection was delayed in 2006 (R2 = 87.4%). Both protein and oil content were affected by the DOY that BPMV was first detected within quadrats in 2006 but not in 2007. This study demonstrated that time of BPMV infection can negatively affect soybean yield, yield components, and grain quality components when BPMV disease risk is high.

Quantification of Yield Loss Caused by Triticum mosaic virus and Wheat streak mosaic virus in Winter Wheat Under Field Conditions.

Triticum mosaic virus (TriMV) and Wheat streak mosaic virus (WSMV) infect winter wheat (Triticum aestivum) in the Great Plains region of the United States. The two viruses are transmitted by wheat curl mites (Aceria tosichella), which also transmit High Plains virus. In a field study conducted in 2011 and 2012, winter wheat cultivars Millennium (WSMV-susceptible) and Mace (WSMV-resistant) were mechanically inoculated with TriMV, WSMV, TriMV+WSMV, or sterile water at the two-leaf growth stage. Chlorophyll meter (soil plant analysis development [SPAD]) readings, area under the SPAD progress curve (AUSPC), grain yield (=yield), yield components (spikes/m2, kernels/spike, 1,000-kernel weight), and aerial dry matter were determined. In Millennium, all measured variables were significantly reduced by single or double virus inoculation, with the greatest reductions occurring in the double-inoculated treatment. Among the yield components, the greatest reductions occurred in spikes/m2. In Mace, only AUSPC was significantly reduced by the TriMV+WSMV treatment in 2012. There was a significant (P ≤ 0.05), negative linear relationship between SPAD readings and day of year in all inoculation treatments in Millennium and in the TriMV+WSMV treatment in Mace. There were significant (P ≤ 0.05), positive linear relationships between yield and SPAD readings and between yield and aerial dry matter in Millennium but not in Mace. The results from this study indicate that under field conditions, (i) Mace, a WSMV-resistant cultivar, is also resistant to TriMV, and (ii) double inoculation of winter wheat by TriMV and WSMV exacerbates symptom expression and yield loss in a susceptible cultivar.

First Report of Sudden Death Syndrome of Soybean Caused by Fusarium virguliforme in South Dakota.

During the 2012 soybean growing season, soybean (Glycine max (L.) Merr.) plants submitted to South Dakota State University Plant Diagnostic Clinic exhibited symptoms typical of sudden death syndrome (SDS) caused by Fusarium virguliforme (Aoki, O'Donnell, Homma, & Lattanzi). In the 2013 soybean growing season, a soybean survey targeting SDS-symptomatic plants was carried out in 20 eastern South Dakota counties between July and August when plants were at the beginning seed and beginning seed maturity growth stages. Soybean plants with SDS-like symptoms were found in eight counties at very low incidence (<3%). Approximately 15 plants per field that had symptoms resembling those of SDS were collected and fungal isolations were made. Leaf symptoms included some necrosis and slight interveinal chlorosis. The tap roots also had areas of necrosis and the vascular system was brown. Isolations were made from the symptomatic tap root sections. The tap root sections were surface sterilized using a 10% NaOCl for 1 min and then rinsed once for 1 min with sterile water before being placed on an acidified potato dextrose agar. Slow growing isolates of F. virguliforme with characteristic blue sporodochia were isolated from these symptomatic plant roots. The conidia were banana-shaped with 4 to 5 septae, a typical characteristic for F. virguliforme. Koch's postulates were performed using a modified layer test method (2). Briefly, the conidia from the isolate (PL1200158 from Yankton county, SD) was used to infest sterile sorghum seed. In the greenhouse, three holes were punched in the bottom of 32 oz. Styrofoam cups. The bottom 11 cm of the cup was then filled with vermiculite. A 2-cm layer of fully colonized sorghum seed was placed on top of the vermiculite. This was covered with a 2- to 5-cm layer of vermiculite. Fifteen soybean cv. Sloan seeds were placed on top of this vermiculite layer and covered with approximately 2 cm more vermiculite for each cup for a total of 12 cups. The temperature in the greenhouse was approximately 23°C with 14 h of light and 10 h of darkness for 21 days. Leaves began to show necrosis and the roots had brown, rotted lesions. Symptoms did not develop on non-inoculated controls. After 5 weeks under greenhouse conditions, the roots of infected plants were removed, surface sterilized, and F. virguliforme was re-isolated. SDS was further confirmed by PCR using primers designed from FvTox1 gene. FvTox1, a single-copy gene, has been found to be highly species specific and primers from this region delineate F. virguliforme from other Fusarium species (1). The PCR product size matched that of expected size. The PCR product was sequenced and a BLAST search matched (100%) only the sequences of F. virguliforme FvTox1 gene (GenBank Accession No. JF440964). The confirmation of SDS in eight counties in South Dakota indicates that SDS may be widespread and a concern for soybean production when conditions are conducive for SDS to develop. References: (1) G. C. Y. Mbofung, et al. Plant Dis. 95:1420, 2011. (2) A. F. Schmitthenner and R. G. Bhatt. Useful Methods for Studying Phytophthora in the Laboratory. Special Circular, Ohio Agricultural Research and Development Center, Wooster, OH, 1994.

Geospatial and temporal analyses of Bean pod mottle virus epidemics in soybean at three spatial scales.

A statewide survey was carried out from 2005 through 2007 to quantify, map, and analyze the spatial dynamics and seasonal patterns of Bean pod mottle virus (BPMV) prevalence and incidence within Iowa. In all, 8 to 16 soybean fields were arbitrarily sampled from 96 counties in 2005 and all 99 counties in 2006 and 2007. Field- and county-scale BPMV prevalence and incidence data were mapped using geographic information systems software. BPMV prevalence was highest in the 2006 soybean growing season, when BPMV was detected in 38.7% of all soybean fields, 91.9% of all counties, and 100% of the agricultural climate districts. BPMV incidence at the field scale was highest in 2006, when mean statewide end-of-season incidence was 24.4%. Spatial analyses indicated that BPMV incidence was spatially clustered at the county scale in all three growing seasons. Prevalence at the county scale was clustered in 2005 and 2007 but not in 2006. Semivariogram analyses at the field scale indicated the presence of significant (P ≤ 0.05) spatial dependence (clustering) at distances ≤23.4 km in 2005, 297.7 km in 2006, and 45.2 km in 2007. Data for county-scale incidence displayed a north (low incidence) to south (high incidence) BPMV gradient in each year of the survey. High county-scale BPMV prevalence and incidence levels in 2006 were significantly associated with BPMV prevalence and incidence in 2007 (P ≤ 0.05). Soybean fields with narrow row spacings (≤38 cm) were associated with higher levels of BPMV incidence. Soybean fields infected with BPMV had a higher probability of infection by Phomopsis pod and stem blight than did non-BPMV-infected fields. This study provides new quantitative tools and information to better understand the seasonal, temporal, and geographical distribution of BPMV disease risk at several spatial scales.

The disappearance of onchocerciasis from the Itwara focus, western Uganda after elimination of the vector Simulium neavei and 19 years of annual ivermectin treatments.

The Itwara onchocerciasis focus is located around the Itwara forest reserve in western Uganda. In 1991, annual treatments with ivermectin started in the focus. They were supplemented in 1995 by the control of the vector Simulium neavei, which was subsequently eliminated from the focus. The impact of the two interventions on the disease was assessed in 2010 by nodule palpations, examinations of skin snips by microscopy and PCR, and Ov16 recombinant ELISA. There was no evidence of any microfilaria in 688 skin snips and only 2 (0.06%) of 3316 children examined for IgG4 were slightly above the arbitrary cut off of 40. A follow up of the same children 21 months later in 2012 confirmed that both were negative for diagnostic antigen Ov-16, skin snip microscopy and PCR. Based on the World Health Organization (WHO) elimination criteria of 2001 and the Uganda onchocerciasis certification guidelines, it was concluded that the disease has disappeared from the Itwara focus after 19 years of ivermectin treatments and the elimination of the vector around 2001. Ivermectin treatments were recommended to be halted.

Occurrence and Distribution of Triticum mosaic virus in the Central Great Plains.

Wheat curl mite (WCM)-transmitted viruses-namely, Wheat streak mosaic virus (WSMV), Triticum mosaic virus (TriMV), and the High Plains virus (HPV)-are three of the wheat-infecting viruses in the central Great Plains of the United States. TriMV is newly discovered and its prevalence and incidence are largely unknown. Field surveys were carried out in Colorado, Kansas, Nebraska, and South Dakota in spring and fall 2010 and 2011 to determine TriMV prevalence and incidence and the frequency of TriMV co-infection with WSMV or HPV in winter wheat. WSMV was the most prevalent and was detected in 83% of 185 season-counties (= s-counties), 73% of 420 season-fields (= s-fields), and 35% of 12,973 samples. TriMV was detected in 32, 6, and 6% of s-counties, s-fields, and samples, respectively. HPV was detected in 34, 15, and 4% of s-counties, s-fields, and samples, respectively. TriMV was detected in all four states. In all, 91% of TriMV-positive samples were co-infected with WSMV, whereas WSMV and HPV were mainly detected as single infections. The results from this study indicate that TriMV occurs in winter wheat predominantly as a double infection with WSMV, which will complicate breeding for resistance to WCM-transmitted viruses.

Effects of Single and Double Infections of Winter Wheat by Triticum mosaic virus and Wheat streak mosaic virus on Yield Determinants.

Triticum mosaic virus (TriMV) is a recently discovered virus infecting wheat (Triticum aestivum) in the Great Plains region of the United States. It is transmitted by wheat curl mites (Aceria tosichella) which also transmit Wheat streak mosaic virus (WSMV) and Wheat mosaic virus. In a greenhouse study, winter wheat 'Millennium' (WSMV susceptible) and 'Mace' (WSMV resistant) were mechanically inoculated with TriMV, WSMV, TriMV+WSMV, or sterile water at the two-leaf growth stage. At 28 days after inoculation, final chlorophyll meter (soil plant analysis development [SPAD]) readings, area under the SPAD progress curve (AUSPC), the number of tillers per plant, shoot and root weight, and total nitrogen and carbon content were determined. In Millennium, all measured variables were significantly reduced by single or double virus infections, with the greatest reductions occurring in the double-infection treatment. In Mace, only final SPAD readings, AUSPC, and total nitrogen were significantly reduced by single or double virus infections. There was a significant (P ≤ 0.05), positive linear relationship between SPAD readings and shoot weight in Millennium but not in Mace. The relationship between total nitrogen and shoot weight was positive, linear, and significant in both cultivars. The results from this study indicate that Mace, a WSMV-resistant cultivar, is also resistant to TriMV, and double infection of winter wheat by TriMV and WSMV exacerbates symptom expression and loss of biomass in susceptible cultivars.

Quantifying the Within-Field Temporal and Spatial Dynamics of Bean pod mottle virus in Soybean.

The prevalence and incidence of Bean pod mottle virus (BPMV) have been reported to be on the increase in the United States but little is known about the temporal and spatial dynamics of this virus within soybean (Glycine max) fields. A quadrat-based sampling method was developed to quantify the within-field spread of BPMV in soybean in 2006 and 2007. Twenty-five 30-cm-long quadrats were established within each row of soybean in field plots consisting of six rows, each 7.6 m long and spaced 0.76 m apart. Four treatments were used to influence the temporal and spatial dynamics of BPMV epidemics. Treatments were: (i) establishment of a point source of BPMV inoculum within soybean plots; (ii) lambda-cyhalothrin insecticide applied at the V1 and R2 growth stages; (iii) establishment of a BPMV inoculum point source, plus the application of foliar insecticide sprays at the V1 and R2 growth stages; and (iv) a nontreated, noninoculated control. All quadrats (census) were sampled beginning 25 days after planting; sampling continued every 8 to 11 days until plants were senescent. Sap from leaf samples was extracted and tested for BPMV by enzyme-linked immunosorbent assay. The incidence of BPMV per treatment was plotted against time to produce BPMV incidence curves for temporal analyses. In addition, positions of BPMV-positive quadrats were mapped for spatial analyses. BPMV was detected within soybean plots on the first sampling date in 2006 (30 May) and on the second sampling date in 2007 (21 June). The rate of BPMV temporal spread within treatments ranged from 0.11 to 0.13 logits/day in 2006 and from 0.05 to 0.07 logits/day in 2007. Doubling times for BPMV incidence among treatments ranged from 5.4 to 6.4 days in 2006 and from 10.0 to 14.1 days in 2007. Soybean plots that had the earliest dates of BPMV detection within quadrats (x) also had the highest BPMV incidence (y) at the end of the growing season (R2 = 66.5 and 70.4% for 2006 and 2007, respectively). Spatial analyses using ordinary runs, black-white join-counts, and spatial autocorrelation revealed highly aggregated spatial patterns of BPMV-infected quadrats over time. Bean leaf beetle population densities were linearly related to BPMV incidence (P < 0.0001) in both years, indicating that BPMV epidemics were greatly influenced by bean leaf beetle population density. To our knowledge, this is the first study to quantify the seasonal temporal and spatial dynamics of BPMV spread within soybean.

Prevalence, incidence, and spatial dependence of soybean mosaic virus in Iowa.

The prevalence of soybean fields with plants infected with Soybean mosaic virus (SMV) in Iowa is assumed to be random, because the primary source of the virus is SMV-infected seed. Data collected from 2,500 soybean fields sampled over a 3-year period as part of the Iowa Soybean Disease Survey (2005 to 2007) were used to evaluate this assumption. SMV was first detected in early June of each year but counties in which it was first detected varied among years. Prevalence at the county scale at end of season was 32.3, 27.3, and 89.9% in 2005, 2006, and 2007, respectively. End-of-season incidence of SMV within SMV-positive counties was 1.5 to 25.0, 1.7 to 24, and 1.8 to 58% in 2005, 2006, and 2007, respectively. The number of fields in which plants infected with SMV were detected increased at the linear rate of approximately one new field every 2 days in 2007, compared with one new field every 22 days (2005) and 21 days (2006), with coefficients of determination (R2) of 93.2 to 96.8% using the linear model. Weak spatial dependence for end-of-season SMV incidence was detected using Moran's Index, indicating that the risk for SMV incidence at the county scale within Iowa at the end of the growing season is not random.

Evaluating the Importance of Stem Canker of Soybean in Iowa.

The relative importance of stem canker of soybean in Iowa compared with other soybean diseases present in the state was assessed using data collected from over 3,400 soybean fields sampled in the Iowa Soybean Disease Survey that was conducted from 2005 to 2007. Symptomatic plant tissues from soybean plants with stem canker symptoms were cultured on acidified potato dextrose agar. The prevalence of stem canker on soybean in 2005 in Iowa was 2.6%; the disease was not detected in 2006 and 2007. In 2005, 63 isolates with Diaporthe/Phomopsis characteristics were collected. To identify isolates to fungal species and variety, single-spored isolates were subjected to polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and sequencing of the internal transcribed spacer (ITS) region. Fourteen isolates were identified as D. phaseolorum var. caulivora (northern stem canker) and 49 as Phomopsis longicolla. To quantify and compare the aggressiveness of D. phaseolorum var. caulivora isolates collected in Iowa, nine isolates were arbitrarily selected for components analysis. Incubation period, rate of lesion expansion, final lesion length, and time to plant death for each isolate were quantified. Significant differences in components of aggressiveness were detected among the nine isolates. Results from this work suggest stem canker is a minor disease of soybean in Iowa.