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Meta-analysis was used to compare yield protection and nematode suppression provided by two seed-applied and two soil-applied nematicides against Meloidogyne incognita and Rotylenchulus reniformis on cotton across 3 years and several trial locations in the U.S. Cotton Belt. Nematicides consisted of thiodicarb- and fluopyram-treated seed, aldicarb and fluopyram applied in furrow, and combinations of the seed treatments and soil-applied fluopyram. The nematicides had no effect on nematode reproduction or root infection but had a significant impact on seed cotton yield response ([Formula: see text]), with an average increase of 176 and 197 kg/ha relative to the nontreated control in M. incognita and R. reniformis infested fields, respectively. However, because of significant variation in yield protection and nematode suppression by nematicides, five or six moderator variables (cultivar resistance [M. incognita only], nematode infestation level, nematicide treatment, application method, trial location, and growing season) were used depending on nematode species. In M. incognita-infested fields, greater yield protection was observed with nematicides applied in furrow and with seed-applied + in-furrow than with solo seed-applied nematicide applications. Most notable of these in-furrow nematicides were aldicarb and fluopyram (>131 g/ha) with or without a seed-applied nematicide compared with thiodicarb. In R. reniformis-infested fields, moderator variables provided no further explanation of the variation in yield response produced by nematicides. Furthermore, moderator variables provided little explanation of the variation in nematode suppression by nematicides in M. incognita- and R. reniformis-infested fields. The limited explanation by the moderator variables on the field efficacy of nematicides in M. incognita- and R. reniformis-infested fields demonstrates the difficulty of managing these pathogens with nonfumigant nematicides across the U.S. Cotton Belt.

A field study was conducted twice in Elizabeth, MS, at on-farm sites in 2010–11 and 2011–12, and twice in 2012–13 at Mississippi State University’s Delta Research and Extension Center in Stoneville, MS, to evaluate glyphosate-resistant (GR) Italian ryegrass control and crop response to fall treatments followed by postemergence herbicide treatments in winter and/or spring. Italian ryegrass was controlled ≥92% and 61% following S-metolachlor and tillage 77 d after fall treatments (DA-FT), respectively. S-metolachlor fall treatment provided 33% greater control than clethodim winter treatment at 21 d after winter treatments (DA-WT). Tillage fall treatment followed by (fb) clethodim winter treatment fb paraquat spring treatment provided similar control (93%) to treatments containing S-metolachlor fall treatment fb a winter or spring herbicide treatment (≥93%) 24 d after spring treatments (DA-ST). Greatest soybean and corn density and yield were also observed following programs containing S-metolachlor fall treatment. Sequential postemergence herbicide treatments were not required to increase corn and soybean density and yield when S-metolachlor was used as a fall treatment. Growers have the best opportunity to maximize GR Italian ryegrass control when S-metolachlor fb a winter or spring herbicide treatment is used.

From 2015 to 2020, 342 isolates of Xanthomonas citri pv. malvacearum (Xcm) were obtained from cotton fields in Texas, including 64 isolates collected from symptomatic cultivars that were thought to be resistant to race 18 strains of Xcm (the predominant race in the United States). Symptoms on highly resistant cultivars prompted concern that a new race of Xcm was present. The 342 isolates were inoculated on a race 18 susceptible (DP 1747NR B2XF) and race 18 resistant (S295) cotton cultivar, and none of the isolates caused blight-type symptoms (water soaking and chlorosis) on S295, indicating that the B12 resistant gene was still beneficial for disease management. Four cultivars, varying in their field response to bacterial blight, were inoculated with each of 17 isolates of Xcm, and the incidence of plants exhibiting bacterial blight symptoms averaged 87% for DP 1747NR B2XF, 51% for partially susceptible NG 4936 B3XF, 16% for partially resistant DP 1646 B2XF, and 0% for S295. Xcm isolates from Texas (11), Georgia (1), and Oklahoma (1) were sequenced, and their type three effectors (T3Es) were predicted. All isolates (Georgia, Oklahoma, and Texas) had the same T3E proteins as previously identified Xcm race 18 isolates (tested for 25 genes), including XopJ. Race 1, 2, 3, and 12 of Xcm included in the comparisons were all missing the XopJ gene. Use of cultivars with the B12 gene is an effective strategy to manage bacterial blight of cotton.

The genus Gaeumannomyces (Magnaporthaceae, Magnaporthales, Sordariomycetes, Ascomycota) includes root-infecting pathogens, saprobes, and endophytes. Morphological, biological, and phylogenetic analyses were employed to identify fungal isolates derived from turfgrass roots colonized with ectotrophic, dark runner hyphae. Phylogenetic trees for partial sequences of the 18S nuc rDNA, ITS1-5.8S-ITS2 nuc rDNA internal transcribed spacer, and 28S nuc rDNA regions and of the minichromosome maintenance complex 7 (MCM7), largest subunit of RNA polymerase II (RPB1), and translation elongation factor 1-alpha (TEF1) genes were obtained via maximum likelihood and Bayesian methods. Our isolates consistently formed a distinct and highly supported clade within Gaeumannomyces. Common and distinctive biological and morphological characters reinforced these findings. Additionally, we conducted pathogenicity evaluations and demonstrated the ability of this fungus to colonize roots of ultradwarf bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davey), its native host, via ectotrophic, dark runner hyphae, causing disease symptoms including root discoloration and reduced root and shoot mass. Altogether, our discoveries enabled recognition and description of a new species, Gaeumannomyces nanograminis, associated with rotted roots of ultradwarf bermudagrass.

Diaporthe seed decay can compromise seed quality in soybean [Glycine max (L.) Merr.] in the warm and humid production areas of the United States during crop maturation. In the current study, 45 isolates of Diaporthe were recovered from seed sampled from soybean fields affected by Diaporthe-associated diseases in eight U.S. states in 2017. The isolates obtained belonged to 10 species of Diaporthe based on morphology and phylogenetic analyses of the internal transcribed spacer, partial translation elongation factor 1-α, and β-tubulin gene sequences. The associated species included D. aspalathi, D. caulivora, D. kongii, D. longicolla, D. sojae, D. ueckerae, D. unshiuensis, and three novel fungi, D. bacilloides, D. flavescens, and D. insulistroma. One isolate each of the 10 species was examined for pathogenicity on seed of cultivar Sava under controlled conditions. Seven days postinoculation, significant differences in the percentages of decayed seeds and seedling necrosis were observed among the isolates and the noninoculated control (P < 0.0001). While the isolates of D. bacilloides, D. longicolla, and D. ueckerae caused a significantly greater percentage of decayed seeds (P < 0.0001), the isolate of D. aspalathi caused the greatest seedling necrosis (P < 0.0001). The observation of new fungi causing Diaporthe seed decay suggests the need for a more comprehensive survey in U.S. soybean producing areas since members of the genus Diaporthe appear to form a complex that causes seed decay.

Target spot, caused by Corynespora cassiicola, is a foliar disease of soybean in the Midsouthern United States. Increased target spot incidence and severity have been observed across parts of Arkansas and Mississippi regularly since 2007. Because target spot resistant cultivars are not available to manage target spot, soybean farmers rely on fungicides to reduce the potential yield losses associated with the disease. In general, fungicides within the quinone outside inhibitor (QoI) class have been the most widely used products for target spot management. As a result of increased and more widespread target spot during the 2016 season, a brief study was conducted using C. cassiicola monoconidial isolates derived from infected leaf tissue from Arkansas (n = 2) and Mississippi (n = 56) soybean to determine whether isolates were resistant to the QoI fungicides. In all, 27 isolates, one from Arkansas and 26 from Mississippi, were determined to contain the G143A substitution that confers complete resistance to the QoI fungicides.

The application of paraquat mixtures with residual herbicides before planting rice is a common treatment in Mississippi, and rice in proximity is susceptible to off-target movement of these applications. Four concurrent studies were conducted in Stoneville, MS, to characterize rice performance following exposure to a sublethal rate of paraquat, metribuzin, fomesafen, and cloransulam-methyl at different application timings. Herbicides were applied to rice at the growth stages of spiking to one-leaf (VEPOST), two- to three-leaf (EPOST), three- to four-leaf (MPOST), 7 d postflood (PFLD), and panicle differentiation (PD). Regardless of application timing, rice injury following exposure to paraquat was ≥45%. Delays in maturity were increased by 0.3 d d−1 following paraquat from emergence through PD. Dry weight, rough rice yield, panicle density, and germination were reduced by 18.7 g, 131.5 kg ha−1, 5.6 m−2, and 0.3%, respectively, per day from application of paraquat at emergence through PD. By 28 d after treatment (DAT), metribuzin injured rice 3% to 6%, and that injury did not translate into a yield reduction. Regardless of application timing, rice injury following fomesafen application ranged from 2% to 5% 28 DAT. Rice exposed to cloransulam-methyl EPOST exhibited the greatest root and foliar injury 21 DAT and 28 DAT, respectively. Additionally, when rice was exposed to cloransulam-methyl EPOST, yield was reduced to 6,540 kg ha−1 compared with a yield of 7,850 kg ha−1 from nontreated rice. Rice yield was negatively affected after paraquat was applied any time after rice emergence. However, applications of paraquat to rice at early reproductive growth stages reduced rough rice yield and seed germination the greatest. Application timing is crucial in determining severity of rice injury. Early-season injury to rice following paraquat application had less effect on yield compared with injury at later stages. Additionally, fields devoted to seed rice production are at risk for reduced seed germination if they are exposed to paraquat during early reproductive growth stages.

Taproot decline (TRD) is a disease of soybean that has been reported recently from the southern United States (U.S.). Symptoms of TRD include foliar interveinal chlorosis followed by necrosis. Darkened, charcoal-colored areas of thin stromatic tissue are evident on the taproot and lateral roots along with areas of necrosis within the root and white mycelia within the pith. Upright stromata typical of Xylaria can be observed on crop debris and emerging from infested roots in fields where taproot decline is present, but these have not been determined to contain fertile perithecia. Symptomatic plant material was collected across the known range of the disease in the southern U.S., and the causal agent was isolated from roots. Four loci, ⍺-actin (ACT), β-tubulin (TUB2), the nuclear rDNA internal transcribed spacers (nrITS), and the RNA polymerase subunit II (RPB2), were sequenced from representative isolates. Both maximum likelihood and Bayesian phylogenetic analyses showed consistent clustering of representative TRD isolates in a highly supported clade within the Xylaria arbuscula species complex in the "HY" clade of the family Xylariaceae, distinct from any previously described taxa. In order to understand the origin of this pathogen, we sequenced herbarium specimens previously determined to be "Xylaria arbuscula" based on morphology and xylariaceous endophytes collected in the southern U.S. Some historical specimens from U.S. herbaria collected in the southern region as saprophytes as well as a single specimen from Martinique clustered within the "TRD" clade in phylogenetic analyses, suggesting a possible shift in lifestyle. The remaining specimens that clustered within the family Xylariaceae, but outside of the "TRD" clade, are reported. Both morphological evidence and molecular evidence indicate that the TRD pathogen is a novel species, which is described as Xylaria necrophora.

Cercospora leaf blight (CLB), caused by Cercospora kikuchii, C. cf. flagellaris, and C. cf. sigesbeckiae, is a serious disease of soybean [Glycine max (L.) Merr.], which is prevalent in the mid-sou...

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.

Information on performance of sequential treatments of quizalofop-P-ethyl with florpyrauxifen-benzyl on rice is lacking. Field studies were conducted in 2017 and 2018 in Stoneville, MS, to evaluate sequential timings of quizalofop-P-ethyl with florpyrauxifen-benzyl included in preflood treatments of rice. Quizalofop-P-ethyl treatments were no quizalofop-P-ethyl; sequential applications of quizalofop-P-ethyl at 120 g ha−1 followed by (fb) 120 g ai ha−1 applied to rice in the 2- to 3-leaf (EPOST) fb the 4-leaf to 1-tiller (LPOST) growth stages or LPOST fb 10 d after flooding (PTFLD); quizalofop-P-ethyl at 100 g ha−1 fb 139 g ha−1 EPOST fb LPOST or LPOST fb PTFLD; quizalofop-P-ethyl at 139 g ha−1 fb 100 g ha−1 EPOST fb LPOST and LPOST fb PTFLD; and quizalofop-P-ethyl at 85 g ha−1 fb 77 g ha−1 fb 77 g ha−1 EPOST fb LPOST fb PTFLD. Quizalofop-P-ethyl was applied alone and in mixture with florpyrauxifen-benzyl at 29 g ai ha−1 LPOST. Visible rice injury 14 d after PTFLD (DA-PTFLD) was no more than 3%. Visible control of volunteer rice (‘CL151’ and ‘Rex’) 7 DA-PTFLD was similar and at least 95% for each quizalofop-P-ethyl treatment. Barnyardgrass control with quizalofop-P-ethyl at 120 fb 120 g ha−1 LPOST fb PTFLD was greater (88%) in mixture with florpyrauxifen-benzyl. The addition of florpyrauxifen-benzyl to quizalofop-P-ethyl increased rough rice yield when quizalofop-P-ethyl was applied at 100 g ha−1 fb 139 g ha−1 EPOST fb LPOST. Sequential applications of quizalofop-P-ethyl at 120 g ha−1 fb 120 g ha−1 EPOST fb LPOST, 100 g ha−1 fb 139 g ha−1 EPOST fb LPOST, or 139 g ha−1 fb 100 g ha−1 EPOST fb LPOST controlled grass weed species. The addition of florpyrauxifen-benzyl was not beneficial for grass weed control. However, because quizalofop-P-ethyl does not control broadleaf weeds, florpyrauxifen-benzyl could provide broad-spectrum weed control in acetyl coenzyme A carboxylase–resistant rice.

Florpyrauxifen-benzyl and quizalofop were available for POST applications in 2018; however, little is known about the response of acetyl-CoA carboxylase (ACCase)–resistant rice cultivars and advanced lines to POST herbicides. A field study was conducted in 2017 and 2018 at Stoneville, MS, to characterize the response of ACCase-resistant rice cultivars and advanced lines to POST applications of florpyrauxifen-benzyl. The imidazolinone-resistant (IR) rice cultivars ‘CL163’ and ‘CLXL 745’, and ACCase-resistant rice cultivars ‘PVL01’, ‘PVL013’, ‘PVL024-B’, ‘PVL038’, ‘PVL080’, and ‘PVL081’were treated with florpyrauxifen-benzyl at 0 (nontreated control for each cultivar) and 58 g ai ha–1 at the four-leaf to one-tiller (LPOST) growth stage. At 14 d after treatment (DAT), PVL01 was injured 5% to 6% greater than CLXL 745, PVL013, and PVL081; however, injury was ≤10% at that evaluation for all cultivars. Similarly, injury was ≤13% for all cultivars 28 DAT. Mature heights were reduced for all cultivars except PVL013 and PVL081. Rough rice yield was ≥100% of the control for all cultivars except PVL081, PVL013, and CL163. Results suggest that florpyrauxifen-benzyl can safely be applied POST to rice cultivars grown in Mississippi as well as ACCase-resistant cultivars that are currently under development.

Off-target paraquat movement to rice has become a major problem in recent years for rice producers in the midsouthern United States. Nitrogen (N) fertilizer is applied to rice in greater quantity and frequency than all other nutrients to optimize rice yield. Two separate field studies were conducted from 2015 to 2018 in Stoneville, MS, to assess whether starter N fertilizer can aid rice recovery from exposure to a sub-lethal concentration of paraquat and to evaluate rice response to different N fertilizer management strategies following exposure to a sub-lethal concentration of paraquat. In both studies, paraquat treatments consisted of paraquat at 0 and 84 g ai ha–1 applied to rice in the two- to three-leaf (EPOST) growth stage. In the starter fertilizer study, N fertilizer at 24 kg ha–1 as ammonium sulfate (AMS) was applied to rice at spiking- to one-leaf (VEPOST), two- to three-leaf (EPOST), or three- to four-leaf (MPOST) growth stages before and after paraquat treatment. In the N fertilizer timing study, N fertilizer at 168 kg N ha–1 was applied in a single four-leaf to one-tiller (LPOST) application or two-, three-, and two four-way split applications. Despite starter N fertilizer applications, paraquat injured rice ≥41%, reduced height 57%, reduced dry weight prior to flooding 77%, delayed maturity 10 d, reduced dry weight at maturity 33%, and reduced rough rice yield 35% in the starter fertilizer study. Similarly, in the N fertilizer timing study, paraquat injured rice ≥45%, reduced height 14%, delayed maturity 10 d, reduced dry weight at maturity 44%, and reduced rough rice yield 50% for all N fertilizer management strategies. Both studies indicate that severe complications in growth and development can occur from rice exposure to a sub-lethal concentration of paraquat. In both studies, manipulation of N fertilizer management did not facilitate rice recovery from early-season exposure to paraquat.

In glyphosate-resistant (GR) cropping systems, paraquat applied in mixtures with residual herbicides prior to crop emergence offers an alternative herbicide mode of action (MOA) to aid in GR weed management. Rice is sensitive to off-target herbicide movement; however, severity of injury can vary with herbicide, rate, and formulation. Therefore, research was conducted from 2015 to 2017 in Stoneville, MS, to characterize rice response to a sublethal concentration of paraquat applied at 84 g ai ha–1 in combination with common residual herbicides. Paraquat plus metribuzin injured rice 68% to 69% 14 and 28 d after treatment (DAT), which was 10% to 13% greater than injury following paraquat alone or paraquat plus fomesafen. Pooled across metribuzin and fomesafen treatments, paraquat reduced rough rice yields 23%. Paraquat plus 10 different residual herbicides injured rice ≥51% 28 DAT and reduced rough rice yields ≥21%. These studies indicate a severe negative impact on rice growth and development following exposure to a sublethal concentration of paraquat alone or in mixture with common residual herbicides. Therefore, applications of paraquat plus residual herbicides to fields in proximity to rice should be avoided if conditions are conducive for off-target movement.

Annual reductions in corn (Zea mays L.) yield caused by diseases were estimated by university Extension-affiliated plant pathologists in 26 corn-producing states in the United States and in Ontario, Canada, from 2016 through 2019. Estimated loss from each disease varied greatly by state or province and year. Gray leaf spot (caused by Cercospora zeae-maydis Tehon & E.Y. Daniels) caused the greatest estimated yield loss in parts of the northern United States and Ontario in all years except 2019, and Fusarium stalk rot (caused by Fusarium spp.) also greatly reduced yield. Tar spot (caused by Phyllachora maydis Maubl.), a relatively new disease in the United States, was estimated to cause substantial yield loss in 2018 and 2019 in several northern states. Gray leaf spot and southern rust (caused by Puccinia polysora Underw.) caused the most estimated yield losses in the southern United States. Unfavorable wet and delayed harvest conditions in 2018 resulted in an estimated 2.5 billion bushels (63.5 million metric tons) of grain contaminated with mycotoxins. The estimated mean economic loss due to reduced yield caused by corn diseases in the United States and Ontario from 2016 to 2019 was US$55.90 per acre (US$138.13 per hectare). Results from this survey provide scientists, corn breeders, government agencies, and educators with data to help inform and prioritize research, policy, and educational efforts in corn pathology and disease management.

The reniform nematode, Rotylenchulus reniformis, can be damaging in silt loam soils that have predominantly supported cotton (Gossypium hirsutum L.) production in the Mid-Southern United States. The objective of this research was to determine the profitability of integrated nematode management options in Mississippi cotton production in soils naturally infested with the reniform nematode. Experiments were conducted near Hamilton, MS, in 2016 and Oswego and Tchula, MS, in 2017. Commercially available seed treatments included a base seed treatment of azoxystrobin + fludioxonil + mefenoxam and seed-applied nematicides including thiodicarb + imidacloprid and fluopyram. In-furrow nematicides included aldicarb and fluopyram + imidacloprid. Lastly, 1,3-dichloropropene was applied preplant to soil followed by cotton seed with and without treatment. Cotton yield was 40 kg/ha greater when 1,3-dichloropropene was applied, and a base fungicide seed treatment was utilized compared with the base seed treatment alone. Cotton yield was at least 73 kg/ha greater when the base seed treatment was followed by aldicarb or fluopyram + imidacloprid in-furrow compared with seed treatments alone. Economic analyses suggested that seed treatment and in-furrow nematicides without 1,3-dichloropropene provided the greatest return on investment.

Rice with enhanced tolerance to herbicides that inhibit acetyl coA carboxylase (ACCase) allows POST application of quizalofop, an ACCase-inhibiting herbicide. Two concurrent field studies were conducted in 2017 and 2018 near Stoneville, MS, to evaluate control of grass (Grass Study) and broadleaf (Broadleaf Study) weeds with sequential applications of quizalofop alone and in mixtures with auxinic herbicides applied in the first or second application. Sequential treatments of quizalofop were applied at 119 g ai ha−1 alone and in mixtures with labeled rates of auxinic herbicides to rice at the two- to three-leaf (EPOST) or four-leaf to one-tiller (LPOST) growth stages. In the Grass Study, no differences in rice injury or control of volunteer rice (‘CL151’ and ‘Rex’) were detected 14 and 28 d after last application (DA-LPOST). Barnyardgrass control at 14 and 28 DA-LPOST with quizalofop applied alone or with auxinic herbicides EPOST was ≥93% for all auxinic herbicide treatments except penoxsulam plus triclopyr. Barnyardgrass control was ≥96% with quizalofop applied alone and with auxinic herbicides LPOST. In the Broadleaf Study, quizalofop plus florpyrauxifen-benzyl controlled more Palmer amaranth 14 DA-LPOST than other mixtures with auxinic herbicides, and control with this treatment was greater EPOST compared with LPOST. Hemp sesbania control 14 DA-LPOST was ≤90% with quizalofop plus quinclorac LPOST, orthosulfamuron plus quinclorac LPOST, and triclopyr EPOST or LPOST. All mixtures except quinclorac and orthosulfamuron plus quinclorac LPOST controlled ivyleaf morningglory ≥91% 14 DA-LPOST. Florpyrauxifen-benzyl or triclopyr were required for volunteer soybean control >63% 14 DA-LPOST. To optimize barnyardgrass control and rice yield, penoxsulam plus triclopyr and orthosulfamuron plus quinclorac should not be mixed with quizalofop. Quizalofop mixtures with auxinic herbicides are safe and effective for controlling barnyardgrass, volunteer rice, and broadleaf weeds in ACCase-resistant rice, and the choice of herbicide mixture could be adjusted based on weed spectrum in the treated field.

The genus Magnaporthiopsis of Magnaporthaceae (Magnaporthales, Sordariomycetes, Ascomycota) contains species that are predominantly necrotrophic pathogens, often producing simple hyphopodia and dark, ectotrophic runner hyphae on plant roots and stems during colonization. Fungal isolates from turfgrass roots with dark and ectotrophic runner hyphae were examined and identified based on morphological, biological, and phylogenetic analyses. Maximum likelihood and Bayesian methods were implemented to obtain phylogenetic trees for partial sequences of the 18S nuc rDNA, ITS1-5.8S-ITS2 nuc rDNA internal transcribed spacer, and 28S nuc rDNA regions, and of the minichromosome maintenance complex 7 (MCM7), largest subunit of RNA polymerase II (RPB1), and translation elongation factor 1-alpha (TEF1) genes. Our isolates consistently formed a distinct and highly supported clade within Magnaporthiopsis. These findings were reinforced by common and distinctive biological and morphological characters. Additionally, we conducted pathogenicity evaluations and demonstrated the ability of this fungus to colonize roots of ultradwarf bermudagrass, one of its native hosts, via ectotrophic, dark runner hyphae, causing disease symptoms including root discoloration and reduced root and shoot mass. Altogether, our discoveries enabled recognition and description of a new species, Magnaporthiopsis cynodontis, which has widespread distribution in the United States.

An isolate of pokeweed mosaic virus (PkMV), referred to as MSFR03, collected from southwestern Mississippi was partially characterized biologically and molecularly. The virus induced pinwheel-like inclusions in infected cells of its natural host (Phytolacca americana L.) and was mechanically transmitted to Chenopodium quinoa, provoking localized infections. The viral genome is 9516 nt in size, excluding the 3′-terminal poly(A) tail, and contains a large ORF encoding a 3056 amino acids long polyprotein and a small overlapping PIPO ORF. Phylogenetic analyses of the whole polyprotein grouped PkMV with turnip mosaic virus (TuMV), potato virus A (PVA) and related potyviruses. Pairwise sequence comparisons showed that PkMV-MSFR03 is a distinct molecular variant of the virus, differing by more than 15% in nucleotide sequences with any of the four previously sequenced isolates from Pennsylvania, Maryland, New Jersey and Arkansas. Our data suggest that the PkMV population in the United States is genetically more diverse than previously known.

Bacterial blight, historically a seed-borne disease of cotton (Gossypium hirsutum) is caused by Xanthomonas citri pv. malvacearum, resulted in significant economic losses prior to development of resistant varieties and implementation of acid-delinting of planting seed. Periodic outbreaks have been associated with seed since the early twentieth century; of note, the disease has experienced a resurgence since 2011. Effective management of bacterial blight is dependent on accurate diagnosis and detection of the pathogen. Currently, detection of X. citri pv. malvacearum is performed by time-consuming microbiological methods. In this study, a novel and sensitive TaqMan-based qPCR protocol was developed to test for X. citri pv. malvacearum in cotton plant tissue. The primers developed are specific to five races of X. citri pv. malvacearum, but not to other Xanthomonas species or cotton-associated nonpathogenic bacteria. The efficiency of this assay was evaluated on artificially inoculated cotton leaves and seed, on naturally infected cotton leaves, and on bolls and seed originating from bacterial blight symptomatic bolls. The protocol’s efficiency from artificially inoculated plant tissue was 102 copies g−1 and 37 copies from 1 g seed for leaves and seed, respectively. In addition, X. citri pv. malvacearum was detected from 94% of the seed samples originating from blight symptomatic bolls. The qPCR protocol provides a rapid and accurate method for diagnosis and detection of bacterial blight and offers a tool for monitoring X. citri pv. malvacearum and potentially reducing its spread in seed.

Diaporthe seed decay can compromise seed quality in soybean [

Growers commonly mix foliar fertilizers with postemergence (POST) herbicides to reduce application costs and/or to decrease soybean injury. Field studies conducted in 2015 and 2016 in Stoneville, MS, evaluated the impact on weed control and soybean (Glycine max (L.) Merr) injury, growth, and yield when combining a blended foliar fertilizer with POST herbicide applications. Herbicide treatments included no herbicide and glyphosate alone and in combination with S-metolachlor, fomesafen, or lactofen. The blended foliar fertilizer was applied at 0, 0.39, and 0.78 kg a.i. ha&minus, 1. In the Weed Control Study, 14 antagonistic effects at various evaluations were detected on Palmer amaranth (Amaranthus palmeri (S.) Wats) and barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.) control 7, 14, and 21 d after treatment (DAT) when a blended foliar fertilizer at 0.39 or 0.78 kg a.i. ha&minus, 1 was mixed with glyphosate alone or combined with S-metolachlor, fomesafen, or lactofen. Of the 14 total effects, nine were detected with foliar fertilizer at the higher rate of 0.78 kg a.i. ha&minus, 1. Seven antagonistic effects were detected for both weed species regardless of herbicide treatment or foliar fertilizer rate. The only treatment combination in which an antagonistic effect was not detected was glyphosate plus lactofen plus foliar fertilizer at 0.78 kg a.i. ha&minus, 1. Blended foliar fertilizer did not influence soybean injury. In the Agronomic Study, blended foliar fertilizer did not impact soybean injury, height, dry wt., nutrient conc., or yield. Foliar fertilizer in combination with POST soybean herbicides did not reduce soybean injury and produced inconsistent effects on weed control across herbicide treatments and between weed species.

Fungicide use in the United States to manage soybean diseases has increased in recent years. The ability of fungicides to reduce disease-associated yield losses varies greatly depending on multiple factors. Nonetheless, historical data are useful to understand the broad sense and long-term trends related to fungicide use practices. In the current study, the relationship between estimated soybean yield losses due to selected foliar diseases and foliar fungicide use was investigated using annual data from 28 soybean growing states over the period of 2005 to 2015. For national and regional (southern and northern United States) scale data, mixed effects modeling was performed considering fungicide use as a fixed and state and year as random factors to generate generalized R2 values for marginal (R2GLMM(m); contains only fixed effects) and conditional (R2GLMM(c); contains fixed and random effects) models. Similar analyses were performed considering soybean production data to see how fungicide use affected production. Analyses at both national and regional scales showed that R2GLMM(m) values were significantly smaller compared to R2GLMM(c) values. The large difference between R2 values for conditional and marginal models indicated that the variation of yield loss as well as production were predominantly explained by the state and year rather than the fungicide use, revealing the general lack of fit between fungicide use and yield loss/production at national and regional scales. Therefore, regression models were fitted across states and years to examine their importance in combination with fungicide use on yield loss or yield. In the majority of cases, the relationship was nonsignificant. However, the relationship between soybean yield and fungicide use was significant and positive for majority of the years in the study. Results suggest that foliar fungicides conferred yield benefits in most of the years in the study. Furthermore, the year-dependent usefulness of foliar fungicides in mitigating soybean yield losses suggested the possible influence of temporally fluctuating abiotic factors on the effectiveness of foliar fungicides and/or target disease occurrence and associated loss magnitudes.

Corn earworm, Helicoverpa zea (Boddie), commonly infests field corn, Zea mays (L.). The combination of corn plant biology, corn earworm behavior in corn ecosystems, and field corn value renders corn earworm management with foliar insecticides noneconomical. Corn technologies containing Bacillus thuringiensis (Bt) Berliner (Bacillales: Bacillaceae) were introduced that exhibit substantial efficacy against corn earworm and may reduce mycotoxin contamination in grain. The first generation Bt traits in field corn demonstrated limited activity on corn earworm feeding on grain. The pyramided corn technologies have greater cumulative protein concentrations and higher expression throughout the plant, so these corn traits should provide effective management of this pest. Additionally, reduced kernel injury may affect physical grain quality. Experiments were conducted during 2011-2012 to investigate corn earworm impact on field corn yield and grain quality. Treatments included field corn hybrids expressing the Herculex, YieldGard, and Genuity VT Triple Pro technologies. Supplemental insecticide treatments were applied every 1-2 d from silk emergence until silk senescence to create a range of injured kernels for each technology. No significant relationship between the number of corn earworm damaged kernels and yield was observed for any technology/hybrid. In these studies, corn earworm larvae did not cause enough damage to impact yield. Additionally, no consistent relationship between corn earworm damage and aflatoxin contamination was observed. Based on these data, the economic value of pyramided Bt corn traits to corn producers, in the southern United States, appears to be from management of other lepidopteran insect pests including European and southwestern corn borer.

The draft genome of Xylaria sp. isolate MSU_SB201401, causal agent of taproot decline of soybean in the southern U.S., is presented here. The genome assembly was 56.7 Mb in size with an L50 of 246. A total of 10,880 putative protein-encoding genes were predicted, including 647 genes encoding carbohydrate-active enzymes and 1053 genes encoding secreted proteins. This is the first draft genome of a plant-pathogenic Xylaria sp. associated with soybean. The draft genome of Xylaria sp. isolate MSU_SB201401 will provide an important resource for future experiments to determine the molecular basis of pathogenesis.

Isolates of Cercospora sojina, causal agent of frogeye leaf spot of soybean (Glycine max), were collected across Alabama, Arkansas, Delaware, Illinois, Indiana, Iowa, Kentucky, Louisiana, Mississippi, Missouri, North Carolina, Ohio, Tennessee, and Virginia and were evaluated for quinone outside inhibitor (QoI) fungicide resistance. Collection of these isolates from these 14 states occurred between 2010 and 2017. QoI fungicide-resistant C. sojina isolates were detected in all 14 states surveyed and represent a total of 240 counties or parishes. In 2017, these 240 counties and parishes represented approximately 13% of the harvested soybean hectares in the United States. In light of this widespread occurrence of QoI fungicide-resistant C. sojina isolates, management of frogeye leaf spot should focus on integrated management practices such as planting resistant soybean cultivars, rotating with nonhost crops, and tilling to speed up decomposition of infested soybean residue. When foliar fungicide application is warranted, fungicide products that contain active ingredients from chemistry classes other than the QoI class should be applied for frogeye leaf spot management.

The reniform nematode, Rotylenchulus reniformis (Linford and Oliveira), remains a common, widespread nematode pest of cotton across the southern United States. Trials were conducted during 2017 at three non-irrigated locations: one location in Hamilton, MS, and two locations in Tchula, MS, in field settings with a history of cotton production and documented economically-damaging reniform nematode populations. Trials were designed to evaluate the response of two cotton cultivars to in-furrow nematicides consisting of aldicarb, 1,3-dichloropropene, and a non-treated control applied for nematode suppression. No significant interactions between cotton cultivar and nematicide were observed. However, treatment with 1,3-dichloropropene produced greater plant biomass, and plant height compared to aldicarb-treated cotton and the nontreated. Nematode densities were suppressed with the use of 1,3-dichloropropene compared to aldicarb and the non-treated control. The use of 1,3-dichloropropene resulted in positive early-season plant growth responses, however, these responses did not translate into greater yield.

Zonate leaf spot (Gloeocercospora sorghi) is a common disease in Sorghum bicolor producing areas of the U.S., but little is known about its biology, virulence and severity on S. bicolor, Zea mays, and related crop grassweeds. Greenhouse studies were conducted to determine and compare the virulence and severity of G. sorghi on 10 commercially available sorghum hybrids, four Z. mays hybrids and selected grassweed species including Sorghum bicolor (grain sorghum and shattercane biotypes) and Sorghum halepense (Johnsongrass), two of the most problematic arable weeds. Plants from the respective species were inoculated with a local G. sorghi isolate and maintained in a dew-chamber at 24 °C for 24 h and then incubated under greenhouse conditions for 4 weeks. Plants were observed for lesion expression and rated using a modified Horsfall-Barrett scale (0–10). The first symptoms of infection were visible within 24 h following inoculation on shattercane and S. bicolor hybrids. Symptoms consisted of small, non-diagnostic purple lesions on the leaves. Results showed that S. bicolor, S. halepense and shattercane were susceptible to G. sorghi. All other species tested in this study were not infected. More particularly, disease severity, increased from a rating of 3 to 10 on sorghum and from 2 to 7 on S. halepense between 2 and 23 days after inoculation, respectively. However, disease severity on shattercane increased rapidly from 3.5 to 10 between 2 and 8 days after inoculation, respectively. Among the sorghum hybrids tested, FFR-322 appeared to be the most resistant to G. sorghi while Pioneer 83G66 appeared to be the most susceptible. Z. mays hybrids were not infected by the fungus used in this study. G. sorghi could be used effectively to manage shattercane and S. halepense infestations occurring in Z. mays and S. bicolor fields consisting of specific G. sorghi-resistant hybrids.

There are numerous early-season pests of cotton, Gossypium hirsutum L., that are economically important, including tobacco thrips, Frankliniella fusca (Hinds), and reniform nematode, Rotylenchulus reniformis (Linford &amp, Oliveira). Both of these species have the potential to reduce plant growth and delay crop maturity, ultimately resulting in reduced yields. A field study was conducted during 2015 and 2016 to evaluate the influence of tillage, at-planting insecticide treatment, and nematicide treatment on pest management, cotton development, and yield. Treatment factors consisted of two levels of tillage (no-tillage and conventional tillage), seven levels of at-planting insecticide treatments (imidacloprid, imidacloprid plus thiodicarb, thiamethoxam, thiamethoxam plus abamectin, acephate plus terbufos, aldicarb, and an untreated control), and two levels of nematicide (no nematicide and 1,3-dichloropropene). There were no significant interactions between tillage, at-planting insecticide treatment, or nematicide for any parameters nor was there a difference in the main effect of nematicide on thrips control or damage. The main effects of tillage and at-planting insecticide treatment impacted thrips densities and damage. The no-tillage treatments and aldicarb in-furrow or acephate seed treatment plus terbufos in-furrow significantly reduced thrips populations. Early-season plant response was impacted by tillage and at-planting insecticide treatment, however, that did not result in significant yield differences. In regard to nematicide treatment, the use of 1,3-dichloropropene resulted in lower yields than the untreated.

Fungicide programs for managing target spot of cotton caused by Corynespora cassiicola were evaluated over 15 site-years in the southeastern United States between 2014 and 2016. Two cultivars, hypothesized to vary in target spot susceptibility, PhytoGen 499WRF (PHY499) and Deltapine 1137B2RF (DPL1137), and four fungicides (azoxystrobin, flutriafol, pyraclostrobin, pyraclostrobin + fluxapyroxad) plus nontreated control, were compared. Fungicide programs consisted of 1) a single application at first flower or disease onset and 2) the first application followed by a second 14 days later. Treatments were applied in a factorial, randomized complete block design. Target spot onset and severity varied among site-years. Except when severity was low, target spot-associated defoliation was greater on PHY499 than on DP1137. Fungicides delayed disease development and defoliation, but application number had little impact. Based on a meta-analysis of 15 site-years, pyraclostrobin-based applications resulted in a 4 to 6% yield preservation, and yield preservation was greater at site-years with early disease onset and >40% target spot associated defoliation. Results suggest a single well-timed application of a pyraclostrobin-based fungicide reduces defoliation and protects cotton yield at locations with high target spot severity. Additional research is needed to identify risk factors for target spot-associated yield losses in cotton production systems.

Fungicide use in the United States to manage soybean diseases has increased in recent years. The ability of fungicides to reduce disease-associated yield losses varies greatly depending on multiple factors. Nonetheless, historical data are useful to understand the broad sense and long-term trends related to fungicide use practices. In the current study, the relationship between estimated soybean yield losses due to selected foliar diseases and foliar fungicide use was investigated using annual data from 28 soybean growing states over the period of 2005 to 2015. At a national scale, a significant quadratic relationship was observed between total estimated yield losses and total fungicide use (R2 = 0.123, P < 0.0001) where yield losses initially increased, reached a plateau, and subsequently decreased with increasing fungicide use. The positive phase of the quadratic curve could be associated with insufficient amount of fungicides being used to manage targeted diseases, application of more-than-recommended prophylactic fungicides under no/low disease pressure, application of curative fungicides after economic injury level, and reduced fungicide efficacy due to a variety of factors such as unfavorable environmental conditions and resistance of targeted pathogen populations to the specific active ingredient applied. Interestingly, a significant quadratic relationship was also observed between total soybean production and total foliar fungicide use (R2= 0.36, P < 0.0001). The positive phase of the quadratic curve may suggest that factors like plant physiological changes, including increased chlorophyll content, photosynthetic rates, water use efficiency, and delayed senescence that have been widely reported to occur after application of certain foliar fungicides could have potentially contributed to enhanced yield. Therefore, the current study provides evidence of the potential usefulness of foliar fungicide applications to mitigate soybean yield losses associated with foliar diseases and their potential to positively impact soybean production/yield at national and regional scales although discrepancies to the general trends observed at national and regional scales do prevail at the local (state) level.

BackgroundFoliar fungicide applications to corn (Zea mays L.) occur at one or more application timings ranging from early vegetative growth stages to mid-reproductive stages. Previous studies indicated that fungicide applications are profitable under high disease pressure when applied during the tasseling to silking growth stages. Few comprehensive studies in corn have examined the impact of fungicide applications at an early vegetative growth stage (V6) compared to late application timings (VT) for yield response and return on fungicide investment (ROI) across multiple locations.ObjectiveCompare yield response of fungicide application timing across multiple fungicide classes and calculate the probability of positive ROI.MethodsData were collected specifically for this analysis using a uniform protocol conducted in 13 states in the United States and one province in Canada from 2014-2015. Data were subjected to a primary mixed-model analysis of variance. Subsequent univariate meta-analyses, with and without moderator variables, were performed using standard meta-analytic procedures. Follow-up power and prediction analyses were performed to aid interpretation and development of management recommendations.ResultsFungicide application resulted in a range of yield responses from -2,683.0 to 3,230.9 kg/ha relative to the non-treated control, with 68.2% of these responses being positive. Evidence suggests that all three moderator variables tested (application timing, fungicide class, and disease base level), had some effect (α = 0.05) on the absolute difference in yield between fungicide treated and non-treated plots ([Formula: see text]). Application timing influenced [Formula: see text], with V6 + VT and the VT application timings resulting in greater yield responses than the V6 application timing alone. Fungicide formulations that combined demethylation inhibitor and quinone outside inhibitor fungicides significantly increased yield response.ConclusionFoliar fungicide applications can increase corn grain yield. To ensure the likelihood of a positive ROI, farmers should focus on applications at VT and use fungicides that include a mix of demethylation inhibitor and quinone outside inhibitor active ingredients.

Soybean (Glycine max L. Merrill) is an economically important commodity for United States agriculture. Nonetheless, the profitability of soybean production has been negatively impacted by soybean diseases. The economic impacts of 23 common soybean diseases were estimated in 28 soybean-producing states in the U.S., from 1996 to 2016 (the entire data set consisted of 13,524 data points). Estimated losses were investigated using a variety of statistical approaches. The main effects of state, year, pre- and post-discovery of soybean rust, region, and zones based on yield, harvest area, and production, were significant on "total economic loss" as a function of diseases. Across states and years, the soybean cyst nematode, charcoal rot, and seedling diseases were the most economically damaging diseases while soybean rust, bacterial blight, and southern blight were the least economically damaging. A significantly greater mean loss (51%) was observed in states/years after the discovery of soybean rust (2004 to 2016) compared to the pre-discovery (1996 to 2003). From 1996 to 2016, the total estimated economic loss due to soybean diseases in the U.S. was $95.48 billion, with $80.89 billion and $14.59 billion accounting for the northern and southern U.S. losses, respectively. Over the entire time period, the average annual economic loss due to soybean diseases in the U.S. reached nearly $4.55 billion, with approximately 85% of the losses occurring in the northern U.S. Low yield/harvest/production zones had significantly lower mean economic losses due to diseases in comparison to high yield/harvest/production zones. This observation was further bolstered by the observed positive linear correlation of mean soybean yield loss (in each state, due to all diseases considered in this study, across 21 years) with the mean state wide soybean production (MT), mean soybean yield (kg ha-1), and mean soybean harvest area (ha). Results of this investigation provide useful insights into how research, policy, and educational efforts should be prioritized in soybean disease management.

Annual decreases in soybean (Glycine max L. Merrill) yield caused by diseases were estimated by surveying university-affiliated plant pathologists in 28 soybean-producing states in the United States and in Ontario, Canada, from 2010 through 2014. Estimated yield losses from each disease varied greatly by state or province and year. Over the duration of this survey, soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) was estimated to have caused more than twice as much yield loss than any other disease. Seedling diseases (caused by various pathogens), charcoal rot (caused by Macrophomina phaseolina (Tassi) Goid), and sudden death syndrome (SDS) (caused by Fusarium virguliforme O’Donnell & T. Aoki) caused the next greatest estimated yield losses, in descending order. The estimated mean economic loss due to all soybean diseases, averaged across U.S. states and Ontario from 2010 to 2014, was $60.66 USD per acre. Results from this survey will provide scientists, breeders, governments, and educators with soybean yield-loss estimates to help inform and prioritize research, policy, and educational efforts in soybean pathology and disease management.

Over the past decade, a soybean root issue of unknown etiology has been observed across a widespread geography in the southern United States. Recently, pathologists began referring to the problem as taproot decline of soybean, based on the appearance of root symptoms. Taproot decline has been observed to cause foliar symptoms in vegetative and reproductive soybean plants ranging in maturity from V6 to R6. Symptom expression can appear similar to other notable root-associated diseases except that taproot decline exhibits a progression of symptom expression from subtle to severe interveinal chlorosis during the season. However, one distinct symptom associated with taproot decline is observed as darkened, black stroma on the taproot and, in some cases, the lateral roots of affected plants. Pathogenicity was confirmed by isolating the suspected fungus from naturally-infected soybean roots in multiple states and completing Koch’s postulates. The causal agent was identified, based on morphological characters and multilocus phylogenetic inference, as a member of the Xylaria arbuscula aggregate. At present, research projects are underway to address the role of the newly described disease and extent of the pathogen in the southern soybean production region in addition to developing integrated strategies for managing the disease.