Soybean cyst nematode (SCN) causes over $1.2 billion in revenue loss annually in the United States and consistently ranks as the most threatening pathogen for soybean. SCN weed hosts have been documented in other states in the eastern Corn Belt, but very little work has been done in the midwestern Corn Belt. To determine alternative SCN weed hosts in South Dakota, 670 whole weed root samples comprising 63 weed species were collected from 48 SCN-positive fields in 13 counties during fall 2016 and spring 2017. Among the 63 weed species, 12 contained SCN juveniles and 7 were confirmed hosts of SCN based on the completion of the SCN life cycle in greenhouse studies. Ranking of female index (FI) for the weed hosts were purple deadnettle (FI = 34.6) > field pennycress (FI = 26.9) > common mallow (FI = 2.04) > shepherd’s purse (FI = 1.89) > white clover (FI = 1.86) > Canada thistle (FI = 1.24) > common cocklebur (FI = 1.10). These results indicate that some weeds can support SCN, and therefore a proactive weed management approach should be employed for fields infested with SCN.

Certain winter annual weeds have been documented as alternative hosts to soybean cyst nematode (SCN), and infestations by such species are common in no-till production fields in the midwestern United States of Indiana, Ohio, and Illinois. The objective of this research was to determine the influence of crop rotation and winter annual weed management on winter weed growth, SCN population density, and crop yield. Two crop rotations (SS and soybean–corn rotation) and six winter annual weed-management systems (autumn-applied herbicide, spring-applied herbicide, autumn + spring applied herbicides, autumn-seeded Italian ryegrass, autumn-seeded wheat, and a nontreated check) were evaluated in long-term, no-tillage systems at West Lafayette, IN, and Vincennes, IN. In the fourth and fifth years of these experiments, the 2-yr corn–soybean rotation generally resulted in increased soybean yield, decreased winter annual weed growth, and reduced SCN population density compared with SS. Autumn or spring herbicide applications or both were a more effective option than cover crops at reducing winter annual weed density. Cover-crop systems generally did not differ from the nontreated check in winter weed density. Between years three and five, winter annual weed SCN hosts in nontreated check plots increased approximately threefold to levels as high as 102 and 245 plants m−2 at West Lafayette, IN, and Vincennes, IN, respectively, which are infestation levels at or above those commonly observed in production fields. However, controlling winter annual weeds did not influence crop yields or SCN population density. The results of these studies suggest that winter weed management, even at the high levels of weed infestation present in these studies, appears to have little value as a tool for SCN management in corn and soybean production systems in the midwestern United States.

Certain winter annual weeds have been documented as alternative hosts to soybean cyst nematode (SCN), and infestations of such species have become common in no-till production fields in the Midwest. This research was conducted to determine the influence of herbicide- and cover-crop-based winter annual weed management systems and crop rotation on winter annual weed growth and seed production, SCN population density, and crop yield. Two crop rotations (continuous soybean and soybean-corn) and six winter annual weed management systems (a nontreated control, fall and spring herbicide applications, spring-applied herbicide, fall-applied herbicide, fall-seeded annual ryegrass, and fall-seeded winter wheat) were evaluated in no-tillage systems from fall 2003 to 2006 at West Lafayette, IN and Vincennes, IN. Fall or spring herbicide treatments generally resulted in lower winter annual weed densities than cover crops. Densities of henbit and purple deadnettle increased over years in the cover crop systems but remained constant in the herbicide systems. Averaged over sites and years, winter annual weed densities were nearly 45% lower in the spring than the fall due to winter mortality. Corn yield was reduced by the cover crops at West Lafayette but not Vincennes. Winter annual weed management system had no influence on soybean yield. SCN population density was reduced by including corn in the crop sequence but was not influenced by winter annual weed management. The density of weedy host species of SCN in the experimental area was relatively low (less than 75 plants m−2) compared to densities that can be observed in production fields. The results of these experiments suggest that inclusion of corn into a cropping sequence is a much more valuable SCN management tool than winter annual weed management. In addition, control of winter annual weeds, specifically for SCN management, may not be warranted in fields with low weed density.

Soybean cyst nematode (SCN) is a major soybean yield–limiting disease in the United States. Henbit, a winter annual species common to no-till fields in the midwestern United States, is known to act as an alternative host for SCN. A simulation was performed to estimate how likely SCN was to reproduce on henbit roots during a 30-yr period in two important soybean production areas of Nebraska. Simulations were conducted using published information on henbit seedling emergence, SCN reproduction on henbit roots, and SCN response to soil temperature. Results indicate that SCN would be able to complete one generation on henbit roots under Nebraska conditions. The SCN reproductive cycle was not likely to be completed before the winter in south central Nebraska, but one SCN generation was predicted to be completed in the fall in 2 out of 30 simulation years (7% likelihood) in southeast Nebraska. Based on our predictions, to reduce the chances of SCN population build-up in the absence of its main host (soybean), weed management in fields infested with both henbit and SCN should be completed after crop harvest in the fall when most henbit seedlings have emerged and are growing but the SCN developing on henbit roots have not yet achieved full maturity in Nebraska.

Fifty-five soybean cyst nematode (SCN)–infested production fields across Indiana were surveyed in March 2004 to assess broadleaf winter weed prevalence. The most frequently occurring weeds were common chickweed (87%), speedwell (83%), buttercup (58%), and henbit (53%). Henbit and wild garlic were present at the highest average densities, both occurring at greater than 50 plants/m2. Based on relative abundance indices, common chickweed and henbit were the most prevalent winter weeds in this survey. As a composite, winter weed hosts of SCN were found in 93% of fields and occurred at an average density of 151 plants/m2. No correlation existed between weed density and SCN egg counts. Frequency, uniformity, density, and diversity indices for individual weed species were generally higher in the southern region of Indiana than in the north. Thus, the region of highest risk for SCN reproduction and population increase on winter weeds in Indiana appears to be in the southern part of the state.

Field observations in Ohio suggested a possible interaction between soybean cyst nematode (SCN) and glyphosate in Countrymark 316 soybean, a transgenic glyphosate-resistant (R) variety that also expresses SCN resistance derived from ‘PI88788’ soybean. To investigate this possible interaction under controlled conditions, greenhouse experiments were conducted in which Countrymark 316 (R) and Corsoy 79 (S = susceptible to glyphosate and SCN) soybean root and shoot weights were measured in response to three concentrations of race 3 SCN inoculum and five glyphosate doses. Experiments were conducted in which glyphosate was applied 9, 18, or 27 d after inoculation (DAI). Data from SCN treatments in the (S) soybean experiments were regressed on glyphosate dosage and fit to a log-logistic dose–response model. SCN–glyphosate interaction in the (S) soybean variety reduced root dry weight of SCN-inoculated plants 6% compared with noninoculated plants when 1.0 kg/ha glyphosate was applied 18 DAI. The most significant interaction of SCN and glyphosate in the (S) variety occurred when glyphosate was applied 27 DAI; the glyphosate dose required to reduce shoot fresh weight 25% was 0.55 kg/ha in the noninoculated control compared with 0.32 kg/ha in plants inoculated with 1,000 SCN eggs/200 cm3 soil. Glyphosate rates of 0.84 and 1.69 kg/ha reduced root dry weights of Countrymark 316 (R) soybean 10 to 13% at the 18 DAI application timing only. Inoculation with SCN reduced shoot fresh weight of (R) soybean 8 to 29% across all experiments, but there was no interaction of glyphosate and SCN in (R) soybean.

Soybean cyst nematode (SCN) is one of the most yield limiting pathogens in U.S. soybean production. Henbit and purple deadnettle are winter annual weeds shown to facilitate SCN reproduction after crop harvest in the eastern Corn Belt. These weeds, along with volunteer soybean that germinates in autumn after harvest, are common to postharvest soybean production fields and provide an opportunity for SCN reproduction and population increase outside of the typical soybean production season. The objective of this experiment was to determine if autumn removal of these weeds and volunteer soybean can influence the winter weed seedbank, plant biomass, and SCN population densities. Microplots were established with or without Lamium spp. and volunteer soybean, and four winter weed removal timings (none, October, December, and May). Dry weights of autumn Lamium spp. were reduced 50% in October when grown in competition with volunteer soybean. SCN juveniles were found in henbit roots at higher densities in October (42 per gram of root) than December (5 per gram of root) and were also found in the roots of volunteer soybean (14 per gram of root) in October. SCN egg population densities were 50% lower in August after the summer fallow period. The results of this experiment suggest that autumn removal of winter annual weeds and volunteer soybean did not reduce SCN populations.

Growers and certified crop advisors (CCAs) across Indiana were surveyed during the winter of 2003 to 2004 to assess their perceptions about soybean cyst nematode (SCN) and use of SCN management practices. Most farmers (57%) and CCAs (72%) surveyed reported a moderate to high level of concern regarding SCN and its potential impact on soybean yield. The majority of those surveyed were also aware that some winter annual weeds can serve as hosts for SCN. Crop management practices specifically aimed at managing the impact of SCN were employed by 55 and 78% of growers and CCAs, respectively. However, only 21% percent of growers said that they had sampled a field for nematodes within the last two years. Growers from eastern and southern Indiana were less likely to be concerned about SCN, to implement SCN management strategies, and to have the soil tested for SCN than growers throughout the rest of the state. In addition, smaller farmers appear to be less concerned and knowledgeable about SCN than those who operate larger farms. The results of this survey suggest that the majority of Indiana growers would likely adopt winter weed control to manage SCN. Also, with respect to winter weed control, future Extension efforts should be focused on southern Indiana where both the risk for SCN reproduction on winter annuals and the need for education on SCN appear to be highest.

In greenhouse experiments, Ohio accessions of 22 weed species representing 13 dicot families were screened as alternative hosts of soybean cyst nematode (SCN, Heterodera glycines). Purple deadnettle (Lamium purpureum), henbit (Lamium amplexicaule), field pennycress (Thlaspi arvense), shepherd's-purse (Capsella bursa-pastoris), and a susceptible soybean (Glycine max) cultivar produced SCN population densities of 510, 155, 73, 1, and 366 cysts/450 cm3 soil, respectively, 5 wk after inoculation with eggs from a race 3 SCN population. Purple deadnettle was also a strong host of race 1 SCN and a weak host of race 6 SCN. Average numbers of eggs/cyst among race 3 hosts were highest in purple deadnettle (357), followed by soybean (292), field pennycress (266), henbit (122), and shepherd's-purse (none detected). To our knowledge, henbit is the only SCN host identified here that has been previously identified as a host. The weeds identified as SCN hosts in this study have a winter annual life cycle in Ohio and may serve as sites for SCN reproduction in infested fields during the early or late growing season and when soybean plants are absent.

A survey of seven production fields in Indiana, Illinois, and Ohio was conducted to assess henbit and purple deadnettle growth and soybean cyst nematode (SCN) development and reproduction on these weeds. Autumn and spring growth of purple deadnettle and henbit was influenced by location within each state. In general, winter annual weeds were larger in size and reached maturity earlier in the spring at the southern sample sites than those in the north. All growth stages of SCN were found to be associated with henbit and purple deadnettle at both autumn and spring sample timings. SCN juveniles were generally found infecting roots at highest abundance in the spring. SCN cyst and egg production also were widespread and occurred to a much higher degree during the autumn than the spring developmental period. The results of this survey indicate that management tactics designed to minimize the potential for SCN reproduction on winter annual weeds would probably be most effective if conducted in the autumn, when the majority of SCN reproduction occurred. However, spring populations of winter annual weeds that harbor SCN juveniles might facilitate additional SCN reproduction and population increase if the weeds are not controlled in a timely manner prior to planting.

Soybean cyst nematode (SCN) is the most yield-limiting pathogen of soybean in the United States. Henbit is a prevalent winter annual weed species in no-till fields and is reported to be an alternative host of SCN. A greenhouse study was conducted to evaluate how the development of SCN on henbit roots was affected by herbicide mode of action and time of herbicide application. Henbit plants were grown in watertight pots placed in a water bath bench that kept soil temperature constant (27 ± 1 C) during the study. Ten d after transplanting, pots were inoculated with approximately 1,000 SCN eggs. At 7, 14, or 21 d after inoculation (DAI), henbit plants were sprayed with recommended dose of either glyphosate (870 g ae ha−1) or 2,4-D (1,070 g ae ha−1). The experiment was arranged in a randomized complete block design with five replications per treatment, and two experimental runs separated in time. At 28 DAI, the total number of SCN cysts and eggs, and plant shoot and root dry weight per pot were determined. Henbit root and shoot biomass increased as the time of herbicide application was delayed. Glyphosate reduced root biomass more than 2,4-D, but no differences in shoot biomass were detected. The number of SCN cysts per henbit plant and eggs per cyst increased as the herbicide application was delayed from 7 to 21 DAI. Glyphosate reduced the number of cysts found on henbit roots more than 2,4-D, especially at earlier application times. On plants treated with glyphosate, SCN-females produced only half the number of eggs of SCN-females on henbit plants treated with 2,4-D, regardless of time of application. These results indicate that early control of henbit plants, especially with glyphosate, can reduce SCN reproduction potential in SCN infested fields.