Over the last decade, corn (Zea mays L.) and soybean [Glycine max L. (Merr.)] commodity prices have fluctuated considerably and, more recently, increases in input prices have narrowed profit margins. Non-traditional cropping systems that can boost profits are of increased interest to farmers in South Carolina, specifically double-cropping soybean behind corn. Within this production system, soybean growth is limited due to inadequate environmental conditions, such as shorter day length, a shortened growing season, cooler temperatures, or premature frost. Applying at-plant or close-to-planting applications of nitrogen fertilizer to ultra-late planted soybean has been recommended in other states and explored by growers to increase overall final plant height (PH) and final height to first fruiting node (HFF) by increasing internode length during the vegetative growth stages to aid harvest efficiency. To determine the impact of an early application of nitrogen fertilizer on ultra-late planted soybean, field studies were conducted in 2022-2024 to evaluate five different rates of ammonium nitrate (34-0-0)-0, 15, 30, 60, and 90 lb of N ac-1-on soybean PH, HFF, and grain yield. Results from these studies showed no significant difference in soybean PH, HFF, or grain yield. However, partial profits were observed at 15 lb of N ac-1, yet the lack of a significant difference makes these findings unlikely to yield a consistent return. Moreover, results from these studies indicate that the use of nitrogen, even in ultra-late soybean production systems, does not increase overall plant growth or yield.

The impact of plant diseases on soybean (Glycine max [L.] Merrill) yield was estimated across 29 states and Ontario, Canada from 2020 to 2024 by university and government plant pathologists. Losses from 29 pathogens or groups of pathogens were estimated at the end of each growing season through a survey and summarized across years and locations. Diseases reduced soybean yield by an estimated 1.2 billion bushels (32.8 million metric tons) valued at $14.6 billion USD for the survey period. Per acre, this estimated mean economic loss was equal to $32.93 USD ($81.37 USD per hectare) across all locations and years, excluding costs such as fungicide seed treatments and foliar applications. Soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) reduced yield by 482.4 million bushels (13.1 million metric tons), a value nearly four times greater than the next greatest cause of yield loss, which was sudden death syndrome (SDS) (caused by Fusarium virguliforme O’Donnell & T. Aoki). Following SCN and SDS, the most significant yield losses were attributed to white mold (caused by Sclerotinia sclerotiorum [Lib.] de Bary), seedling diseases (caused by various pathogens), Phytophthora root and stem rot (caused by Phytophthora sojae Kaufm. & Gerd.), and root-knot nematodes (Meloidogyne spp.), in descending order. The most important diseases in the southern U.S. were generally different from those in the northern U.S. and Ontario. Data presented here will enable government agencies, scientists, educators, commodity groups, funding organizations, and plant breeders to enhance and prioritize policy, research, funding, and education regarding soybean disease management.

With fewer agrichemical compounds and molecules being discovered by private industry, innovative ways of using current modes of action and application technologies are not only necessary but imperative to maintain and improve pest management strategies. This research was conducted during 2019 and 2020 at the Edisto Research and Education Center in Blackville, SC. The objective was to determine if sprayer droplet size (150-900 μm) had an impact on the efficacy of a standard insecticide used to control tobacco thrips, Frankliniella fusca (Hinds), in cotton, Gossypium hirsutum (L.). Three separate fields were used where 1- to 2-leaf cotton was sprayed with Orthene 97SG (acephate) applied at a rate of 197 g ai ha-1 to control thrips. Treatments consisted of droplet diameters of 150, 300, 450, 600, 750, and 900 μm. In 2019, acephate applied at a droplet size of 450 μm resulted in the greatest number of thrips on cotton 3 days after application (DAA) when compared with all other droplet sizes. Visual injury ratings at 3 DAA were greater on cotton where acephate was applied at 300-μm droplets when compared with other droplet sizes. In 2020, acephate applied at a droplet size of 150 μm resulted in the lowest number of thrips on cotton at 14 DAA when compared with all other droplet sizes. Based on these results, South Carolina cotton farmers might have more flexibility in nozzle selection and droplet size ranges when using acephate to effectively control thrips in cotton than previously hypothesized.

Fungicides including active ingredients in the demethylation inhibitor group (Fungicide Resistance Action Committee Group 3) are used to manage corn diseases such as northern corn leaf blight, caused by Exserohilum turcicum. This study assessed the level of sensitivity to the demethylation-inhibiting fungicide flutriafol on a population of 81 E. turcicum isolates collected from across the United States in 2020. Sensitivity to flutriafol for E. turcicum was assessed using fungicide-amended media to determine the effective concentration needed to limit hyphal growth by 50%. The mean absolute EC50 values of the overall population calculated using the four-parameter log-logistic and Weibull2 four-parameter models were 2.1881 and 3.2643 mu g/ml, respectively. The growth of most isolates (n = 70, 86.4%) was completely inhibited by 1 mu g/ml of flutriafol. However, the growth of seven isolates (8.6%) was only completely inhibited at 10 or 100 mu g/ml, and complete inhibition was not observed at 100 mu g/ml for four isolates (4.9%). These results suggest that there may be isolates of E. turcicum in the United States that are resistant to flutriafol. Additional fungicide sensitivity screening is critical to monitor the development of fungicide resistance in U.S. populations of E. turcicum.

Plain Language SummaryCompared to certain other nematodes, limited research has been reported for ring nematode (Mesocriconema ornatum) in peanut. To explore relationships with soil texture characteristics and to examine samples for consistency of species identity, peanut fields in six South Carolina counties were surveyed for ring nematodes. Peanut ring nematode was found in 59% of examined field samples. Increased numbers of peanut ring nematodes were associated with soils with increased sand content and decreased clay content. Ring nematode samples were identified as Mesocriconema ornatum. Results from this survey serve as a resource and reference for future work.

The reniform nematode, Rotylenchulus reniformis Linford & Oliveira, 1940 is one of the most important yield-limiting pathogens of agronomic and vegetable crops across tropical and subtropical climates worldwide. Monitoring the distribution of nematode species across the United States can be helpful to identify areas where scouting and management are needed. Given that R. reniformis has been detected in new states and new counties on field crops since the last report nearly 35 years ago, an updated map is needed. The map created herein is an updated resource summarizing the distribution of R. reniformis on field crops (e.g., agronomic and vegetable crops) at the county level across the contiguous United States.

The southern root-knot nematode, Meloidogyne incognita (Kofoid and White, 1919) Chitwood, 1949, is one of the most important, yield-limiting pathogens of agronomic and vegetable crops in the United States and worldwide. It was first reported on cotton ( Gossypium hirsutum L.) in Alabama in the United States. Since then, it has been reported in many states across the United States. These reports include detections in greenhouses, nurseries, or home gardens but do not provide information on where this species persists from year to year in field soils. Furthermore, these reports do not provide distribution information within each state in individual counties. This report summarized the distribution of M. incognita on field crops (e.g., agronomic and vegetable crops) by county for each state across the continental United States.

Meloidogyne enterolobii is an aggressive root-knot nematode (RKN) species that has emerged as a significant pathogen of sweetpotato in the Southeastern United States. M. enterolobii is spread primarily through the movement of infected ‘seed’ sweetpotatoes used for propagation. The RKN resistance in commercially grown sweetpotato cultivars has proven ineffective against this nematode. Detecting RKN in sweetpotato by eye is unreliable, and further distinguishing M. enterolobii from other RKN species that infect sweetpotato is labor intensive; relying on molecular tests conducted on individual nematodes dissected out of host roots by trained technicians. Here, we have developed a high-throughput survey method to collect skin samples and extract total DNA from batches of sweetpotato storage roots. Combining this method with species-specific PCR assays allowed for quick and sensitive detection of M. enterolobii and other RKN species infecting sweetpotatoes. We tested this method using batches of infected storage roots at varying levels of M. enterolobii infection. We also inoculated skin samples with varying numbers of individual M. enterolobii eggs to determine the method’s detection threshold and used this method to conduct surveys for RKN on fresh market sweetpotatoes. Our results show that this method can consistently and reliably detect M. enterolobii in sweetpotato batches at levels as low as 2 eggs per 10 mL skin sample. This method will be a useful tool to help screen for the presence of M. enterolobii in ‘seed’ sweetpotatoes before they are replanted, thereby helping to slow the spread of this nematode to M. enterolobii-free sweetpotato growing operations.

Planter downforce could unify crop emergence by maintaining uniform seeding depth while planting. This research was conducted to determine if planter downforce rate impacted soybean [Glycine max (L.) Merr.] emergence and grain yield in South Carolina. The effects of tillage type, gauge wheel width, and downforce rate (0-300 lbf in 50-lbf increments) on soybean were evaluated at the Edisto (EREC) and Piedmont (PREC) Research and Education Centers in South Carolina. At EREC, a downforce rate over 200 lbf resulted in decreased plant emergence compared with 0, 50, 100, and 150 lbf. A downforce rate of 0 and 50 lbf had a reduced number of emerged plants at 2, 3, and 4 d after emergence compared with rates over 150 lbf at PREC. As downforce rate increased, the depth at which seed were planted increased up to 35% of the original planting depth at EREC. Planter downforce rate appears to influence overall soybean emergence. However, uniform emergence in soybean does not appear to impact grain yield in these production scenarios in South Carolina.

Soybean (Glycine max [L.] Merrill) yield losses as a result of plant diseases were estimated by university and government plant pathologists in 29 soybean producing states in the United States and in Ontario, Canada, from 2015 through 2019. In general, the estimated losses that resulted from each of 28 plant diseases or pathogens varied by state or province as well as year. Soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) caused more than twice as much loss as any other disease during the survey period. Seedling diseases (caused by various pathogens), Sclerotinia stem rot (white mold) (caused by Sclerotinia sclerotiorum [Lib.] de Bary), and sudden death syndrome (caused by Fusarium virguliforme O’Donnell & T. Aoki) caused the next greatest yield losses, in descending order. Following SCN, the most damaging diseases in the northern United States and Ontario differed from those in the southern United States. The estimated mean economic loss from all soybean diseases, averaged across the United States and Ontario, Canada was US$45 per acre (US$111 per hectare). The outcome from the current survey will provide pertinent information regarding the important soybean diseases and their overall severity in the soybean crop and help guide future research and Extension efforts on managing soybean diseases.

Meloidogyne enterolobii (syn. mayaguensis) is an emergent species of root-knot nematode that has become a serious threat to sweet potato (Ipomoea batatas) production in the southeastern United States. The most popular sweet potato cultivars grown in this region are highly susceptible to M. enterolobii. As a result, this pest has spread across most of the sweet potato growing counties in the Carolinas, threatening the industry as well as other crops in the region. The development and release of new sweet potato cultivars with resistance to M. enterolobii would help to manage and slow the spread of this pest. To support sweet potato resistance breeding efforts, 93 accessions selected from the U.S. Department of Agriculture germplasm collection and breeding programs in the United States were screened to identify 19 lines with strong resistance to M. enterolobii. The resistance in these accessions was tested against two M. enterolobii isolates that were collected from sweet potato production fields in the Carolinas. These isolates were found to have distinct pathotypes, with galling and nematode reproduction differences observed on cotton as well as sweet potato. This study is the first report of intraspecific pathotypic variation in M. enterolobii, and it identifies sweet potato germplasm with resistance against both pathogenic variants of this nematode.