Cercospora leaf spot (CLS), caused by Cercospora beticola, poses a significant threat to the yield stability and profitability of the sugar beet industry by negatively impacting recoverable sucrose, yield tonnage, and sugar extraction. In North Dakota and Minnesota, growers rely heavily on quinone outside inhibitors (QoIs) and demethylation inhibitors (DMIs) to provide effective control of CLS, resulting in several CLS epidemics because of widespread resistance to QoIs and DMIs. Copper-based chemicals in various formulations with different active ingredients have a different mode of action compared with QoIs and DMIs and therefore could be used to manage these resistant populations of C. beticola. One in vitro study evaluated the sensitivity of QoI- and/or DMI-resistant C. beticola isolates to eight copper-based products and one sulfur-based product. An in vivo study was conducted in a glasshouse on sugar beet plants to assess the efficacy of copper-based fungicides alone and in mixtures with a sulfur-based product in controlling CLS. The results showed that copper-based fungicides inhibited spore germination of DMI- and QoI-resistant C. beticola isolates, with the EC50 values ranging from 1.73 to 7.52 mu g/ml. The copper-based fungicides significantly reduced CLS severity, and their efficacy was enhanced by a sulfur-based product in a mixture. These findings suggest that copper-based fungicides that inhibit spore germination could provide an effective means for controlling C. beticola. These compounds represent a valuable management tool that could be used as a mixing partner or alternating with single-site resistance risk fungicides to sustain CLS control and to prevent fungicide resistance buildup.
Red crown rot (RCR) of soybean, caused by Calonectria ilicicola, is a significant soilborne disease that typically manifests itself during the flowering stages. Although seed treatments have been employed for RCR control, no method has been developed to provide protection throughout the entire soybean cultivation period. Therefore, we sought to evaluate the efficacy of fungicides applied to stems near the soil surface 4 weeks after emergence. Between 2022 and 2024, we conducted trials in soybean fields in which RCR has occurred frequently, in Toyama Prefecture, central Japan. Identical field trials could not be repeated annually owing to the number of fields and the field size. Thus, data from different trials were integrated and analyzed using a network meta-analysis. The analysis revealed substantial heterogeneity and inconsistency for both disease incidence and a disease severity index derived from midpoint-transformed severity scores. Contrastingly, yield showed low heterogeneity but significant inconsistency. Despite these limitations, all treatments efficaciously reduced disease severity. Additionally, most treatments improved the yield. Fluopyram (2.09 kg a.i./ha) applied twice and pydiflumetofen (0.92 kg a.i./ha) applied twice exhibited especially strong effects against disease severity compared with the nontreated control, with mean differences of -52.060 and -50.191, respectively. These findings suggest that further investigation of the optimal application methods and timing could facilitate the development of a comprehensive RCR management strategy throughout the soybean cultivation period.
Lethal bronzing (LB) is a devastating phytoplasma disease that affects over 20 palm species. The disease is widespread in the state of Florida and causes significant economic losses to a variety of stakeholders, including nurseries, landscape companies, private homeowners, local municipalities, and the state government. To aid stakeholders in managing LB on properties, palm samples are screened routinely for phytoplasma at the University of Florida Fort Lauderdale Research and Education Center. Although the priority of these data is to aid stakeholders, they also serve as a useful data collection tool that allow for better understanding of the epidemiology of the disease. In this study, data from 2017 to 2024 were assessed to better understand seasonal trends in new infections, especially in the context of vector populations. Over the period of 8 years, a distinct seasonal trend was observed in the number of positive detections of LB, with the majority of positives occurring from January to May, significantly dropping from June to December. Populations of the vector were monitored and displayed peak activity in September. The relationship observed supports the observations of a 4- to 8-month latent period after peak vector activity. These data provide valuable insights into the epidemiology of LB in Florida and allow for a more precise timing of monitoring and management efforts.
Annual ryegrass (Lolium multiflorum) is a forage and cover crop that is grown for seed in the Willamette Valley of Oregon before being exported globally. The seed gall nematode, Anguina funesta, is a plant-parasitic nematode affecting annual ryegrass in this seed production region, and its detection in seed lots frequently results in rejection by international trade partners. Seed galls are similar in size to healthy annual ryegrass seed and difficult to separate in the cleaning process. In this study, two types of seed cleaners, an air screen and a gravity table cleaner, were evaluated for their ability to remove seed galls from infested annual ryegrass in commercial seed lots. For both cleaners, four air speeds were evaluated on two replicate samples from two commercial seed lots. The air screen cleaner removed galls from healthy seed at a range of airspeeds, but mid-range air speeds led to the highest reduction in galls with the lowest loss of clean seed (120 cubic feet per minute [CFM]). The gravity table was highly effective at separating galls from healthy seed, leading to significant gall reductions across clean cuts for three of four tested air speeds (40 to 172 CFM). This study indicates that seed cleaning is a useful tool for mitigating seed gall nematode infection of annual ryegrass seed. By reducing the risk of seed lot rejections and lowering the initial inoculum in saved seed, seed cleaning can help protect Oregon's grass seed industry from this pest.
Grape downy mildew, caused by the oomycete pathogen Plasmopara viticola, is one of the most destructive diseases of cultivated grapes worldwide. Although fungicide efficacy and fungicide resistance have been documented in P. viticola in wine grapes (i.e., Vitis vinifera and Vitis interspecific hybrids), limited information exists for juice grapes (i.e., Vitis labrusca). Small-plot trials were conducted in 2021 and 2022 in a mature 'Niagara' vineyard in Fennville, MI, to evaluate fungicide efficacy and monitor resistance development. Disease pressure differed markedly between years: the untreated control (UTC) reached 34% incidence and 26% severity in 2021 versus 90% incidence and 57% severity in 2022. Across both years, mandipropamid (FRAC 40), cyazofamid (FRAC 21), and fenamidone (FRAC 11) provided the most consistent control, reducing incidence and severity AUDPC values by >70% compared with the UTC (2,149.5 for incidence, 807.4 for severity). Molecular analysis of 24 P. viticola isolates collected in 2022 confirmed that all belonged to P. viticola clade aestivalis. The G1105S mutation associated with resistance to carboxylic acid amides was not detected, but the G143A mutation conferring resistance to quinone outside inhibitor fungicides was present in 12 isolates. These findings provide fungicide efficacy data for juice grape downy mildew management and highlight the need for continued resistance monitoring to sustain long-term control.
Seed infestation is an important factor contributing to the dissemination of Pseudomonas syringae in vegetable crops. However, the broad ecological and genetic diversity found within the bacterial species has hindered a precise understanding of the populations responsible for phytosanitary disorders associated with commercial zucchini squash seed production. Here, we genotyped an international collection of over 260 P. syringae strains, as well as other cucurbit-associated bacteria that were primarily isolated from zucchini squash seedling grow-out assays using REP (REP1R-I and REP2-I) and BOX (BOXA1R) PCRs, as well as through sequence analysis of the partial citrate synthase gene. Although the population associated with zucchini squash seeds spanned the diversity of P. syringae phylogroup 2, the hybrid clade 2b-a was the dominant genetic group and comprised 78% of this population, followed by clade 2a at 13%. Seed and spray inoculation assays indicated that clade 2a and 2b-a strains induced severe foliar blighting and stunting of zucchini squash seedlings, whereas strains from other genetic groups were significantly less aggressive. Subsequently, a dual-probe real-time PCR assay targeting the syringolin biosynthesis gene, sylC, was developed to distinguish between P. syringae populations deemed to pose either a high or low phytosanitary risk to zucchini squash seed, based on prevalence and pathogenicity phenotyping. The sylC assay was then multiplexed with an internal positive control to enable use in routine seed health testing. The results of this study elucidate the diversity of the P. syringae population associated with zucchini squash seed production and help to improve seed-health testing methods.
Root rot occurrence has been a growing concern among soybean farmers. In 2020, a fungal isolate was collected from a soybean root symptomatic of root rot from North Dakota. The isolate was cultured in potato dextrose agar, and the morphology was observed. The colony morphology and microscopic features closely matched descriptions of Clonostachys rhizophaga. For confirmation of fungal identity using molecular techniques, DNA was extracted from the pure fungal culture and its subcultures. Multiple genomic regions were used for polymerase chain reaction (PCR). Sequencing of the PCR products followed by BLAST analysis in the NCBI nucleotide database and alignment to the C. rhizophaga reference genome showed high similarity for all loci. Phylogenetic analysis based on beta-tubulin sequences placed the isolate within the C. rhizophaga clade. Among all loci analyzed, the beta-tubulin gene provided the highest species-level resolution, clearly distinguishing C. rhizophaga from other Clonostachys taxa. The molecular evidence confirmed the isolate as C. rhizophaga. Pathogenicity tests were conducted by inoculating the soybean cultivar Barnes. Infected plants showed symptoms of taproot and lateral root necrosis accompanied by root discoloration in two experiments. Fungal DNA reisolated from symptomatic roots, followed by PCR and sequencing, confirmed the isolate as C. rhizophaga. To our knowledge, this is the first report of C. rhizophaga infecting soybean in North Dakota and in the United States.
Stemphylium leaf blight of onion, caused by Stemphylium vesicarium, has caused significant losses in recent harvests, especially during the bulb formation period. This trial evaluated the effect of spraying seven fungicides on the area under the disease progress curve (AUDPC) and on the commercial yield of onions, under natural field inoculation. All treatments differed from the nontreated control in terms of AUDPC and yield. Foliar sprays using difenoconazole + pydiflumetofen, fluazinam, and fluopyram resulted in the highest yields. This information may assist producers and technicians in adopting better disease management strategies.
Among the diseases that affect blackberries, leaf anthracnose is one of the least studied and has become increasingly important in recent years, especially in nurseries, where the responsible pathogen causes regressive stem death after pruning. In October 2023 and 2024, severe anthracnose symptoms were observed on blackberry leaves in Los Reyes, Michoacan, Mexico. The fungi isolated from diseased plants were identified by morphology and phylogenetic analyses as Colletotrichum karstii. The pathogenicity of the fungi was demonstrated by inoculating each isolate with a conidial suspension onto healthy blackberry plants, which exhibited characteristic disease symptoms after 7 days. This is the first report of C. karstii causing leaf anthracnose in blackberry in Mexico. Anthracnose in blackberry plants is an emerging disease impacting commercial fields in Mexico. Therefore, it is essential to explore its diversity and develop effective management strategies.
Small vegetable farms typically grow a wide diversity of crops, frequently use season extension techniques such as high tunnels, and are more likely to adopt organic practices for pest and nutrient management. These production characteristics can have significant impacts on soil nematode communities, including both plant-parasitic nematodes (PPNs) and entomopathogenic nematodes (EPNs). We conducted a targeted survey of PPNs and EPNs on 18 small vegetable farms in Indiana. Of the 24 samples collected, we found that PPNs were widespread (95.8% of samples), while EPNs were also common (66.7%). Nine PPN genera were detected, with spiral (Helicotylenchus spp.), lesion (Pratylenchus spp.), dagger (Xiphinema spp.), and root-knot (Meloidogyne spp.) being the most prevalent. Spiral nematode population densities were especially high, exceeding 5,000 individuals per 500 cm3 of soil in three samples. High populations of lesion nematodes were also observed. Root-knot nematodes were detected in 50% of samples, with 16.7% of all samples exceeding the action threshold. PPN abundance was significantly higher in organically managed high tunnel soils compared with organic open-field soils. Co-occurrence analysis revealed no significant relationships between PPNs and EPNs. This survey provides the first baseline data on the prevalence and abundance of PPNs and EPNs on small vegetable farms in Indiana. These results will support the development of management strategies for PPNs and improve understanding of the potential role of EPNs in insect pest management on small vegetable farms.
Caliciopsis canker disease (CCD) is caused by multiple Caliciopsis species infecting various North American conifers, with Caliciopsis pinea on eastern and western white pines being the most extensively characterized. Symptoms typically include lower branch flagging, sunken resinous cankers, and bark cracking, with severity influenced by environmental stressors such as drought and stand density. The disease is identifiable by the distinctive eyelash-like mazaedia of the pathogen, but species-level diagnosis requires microscopic or molecular confirmation due to overlapping host ranges. This guide documents updated symptomology for C. pseudotsugae on Douglas-fir, discusses geographical ranges of the disease, and provides diagnostic details to support accurate identification and management of CCD across hosts.
Purple spot, a fungal disease caused by Stemphylium vesicarium, renders spears unmarketable and, on the fern, causes premature defoliation, which can decrease the next year's yield and quality. Fungicides, including azoxystrobin, mancozeb, and chlorothalonil, are applied to the foliage according to the TOMCAST disease forecaster at 15 disease severity values to manage purple spot disease. The objective of our study was to identify fungicides that control purple spot disease on asparagus fern. The ability of fungicides to provide extended protection was of interest. Twelve fungicides, alternated with chlorothalonil, were applied to 'Sequoia' asparagus fern every 9 to 11 days and compared with an untreated control in 2022 and 2023. Relative area under the disease progress curve (rAUDPC) data indicated that all treatments within and beyond the interval period limited purple spot disease compared with the control except for fluopyram + pyrimethanil (2022) and pyrimethanil (2022). For industry standards, azoxystrobin had a lower disease severity than the control both within and beyond the treatment interval. Pydiflumetofen + fludioxonil and fluxapyroxad + pyraclostrobin consistently had the lowest rAUDPC among unregistered fungicides within and beyond the treatment interval. The registration of new fungicides can protect the fern from purple spot and expand management options for growers.
Damping-off of soybean caused by soilborne oomycetes of the genera Globisporangium and Pythium pose a significant threat to soybean production, reducing emergence and yield in North America. Metalaxyl and metalaxyl-M are widely used against oomycetes in soybeans and corn; however, the repeated use of these active ingredients might lead to reduced sensitivity of some populations, increasing the interest in potential alternative active ingredients. Few field studies have assessed the effect of commercially available fungicide seed treatments on damping-off caused by these pathogens. This study evaluated the efficacy of fungicide seed treatments against Globisporangium and Pythium species across North America. In 2024, eight field trials were conducted in Indiana, Iowa, Ohio, Ontario, Michigan, North Dakota, Tennessee, and Wisconsin. Trials in Ohio, Ontario, and Tennessee relied on natural inoculum, whereas others were infested at planting with different pathogen species. Five commercial fungicide seed treatments were tested at label rates: (i) imidacloprid, mefenoxam, fluoxastrobin, and prothioconazole; (ii) clothianidin, ethaboxam, ipconazole, and metalaxyl; (iii) inpyrfluxam; (iv) thiamethoxam, mefenoxam, fludioxonil, and sedaxane; and (v) thiamethoxam, picarbutrazox, mefenoxam, fludioxonil, and sedaxane. A nontreated control was included. Fungicide seed treatment significantly improved seed emergence at the growth stages VC (P = 0.0178) and V2 (P = 0.0056). All treatments showed a positive yield effect compared with the nontreated control, although the differences were not statistically significant (P > 0.7081). These findings suggest that seed treatments provide protection against damping-off, but further research is needed to clarify their utility in soybean production, particularly under low seeding rates.
On 2 October 2025, at a wholesale nursery in Albemarle County, VA, approximately 40 out of 100 Betula nigra plants in 11.4-liter containers were observed with light brown, zonate lesions and sclerotia on the leaves. Closer inspection revealed hypophyllous, pyramidal sporophores where the lesions formed, measuring 234 to 482 mu m long and 75 to 111 mu m wide (average 433 & times; 97 mu m, n = 10). Necrotic leaf tissue from three plants was surfaced sterilized with 70% ethanol and cultured on potato dextrose agar medium. DNA was extracted from three isolates (GS25-AE41, GS25-AE42, and GS25-AE43), and they were Sanger sequenced. All three isolates had identical ITS sequences. A 510-bp fragment of the internal transcribed spacer region and a 1,146-bp fragment of the 28S ribosomal RNA from isolate GS25-AE41 were deposited into NCBI GenBank under accessions PX572933 and PX890849, respectively. Koch's postulates were fulfilled by placing agar plugs colonized with isolate GS25-AE41 mycelia facedown on 15 wounded B. nigra leaves. Grovesinia moricola was isolated from 12 out of 15 leaves, while the control leaves did not form lesions. The cultures from the inoculated leaves had a 100% ITS sequence homology to isolate GS25-AE41. G. moricola has been reported from Japan on Corylus (Betulaceae), but this is the first report of the fungus infecting a host in the genus Betula.
Vascular streak dieback (VSD) has recently become a significant issue affecting woody ornamental production, with eastern redbud increasingly impacted in the United States. Plants affected by VSD typically show symptoms such as foliar scorch, shoot dieback, and internal vascular discoloration that appear as a marbled pattern when stems are cross-sectioned. This study examined the performance of fungicide treatments for suppressing VSD in eastern redbud under field conditions in McMinnville, TN. Disease development was monitored through evaluations of leaf scorch, defoliation, and phytotoxic responses, and treatment effects were compared using the area under the vascular streak dieback progress curve. Findings from this work provide practical information to aid U.S. nursery growers in managing VSD more effectively.
Guava trees exhibiting symptoms of root-knot and foliar yellowing were observed in a backyard orchard in Juan Jos & eacute; R & iacute;os, Sinaloa, Mexico. Based on a combination of morphological characteristics, detection using species-specific primers, and phylogenetic analysis employing ITS and coxI sequences, the nematode was identified as Meloidogyne enterolobii. The pathogenicity of M. enterolobii was confirmed by inoculating guava seedlings, which consistently developed root galling symptoms and exhibited a reproduction factor of 21.2 at 110 days postinoculation. This study constitutes the first report of M. enterolobii causing root-knot disease in guava in Mexico.
Community observations in Utqia & gdot;vik, AK, noted symptoms of rust disease on dwarf willow (Salix spp.). Morphological characteristics and sequencing analysis of infected leaves collected in July 2020 identified the rust as Melampsora laricis-epitea. DNA sequencing of the 28S rDNA region confirmed 99.89% identity with M. laricis-epitea isolates from North America and Europe. Comparative morphology and sequence analysis of Spanish specimens hosted at Purdue University's Arthur Fungarium (PUR) on Salix atrocinerea also matched M. laricis-epitea, representing the first confirmed record of this rust on this host in Spain. Our work extends the known range of M. laricis-epitea into Alaska and highlights its potential broader establishment across North America. Given the ecological and cultural significance of willows in Arctic ecosystems as well as their use in biomass cultivation, improved taxonomic resolution and monitoring of Melampsora species are essential for understanding their impacts and managing potential disease risks.
During summer 2025, yellowing, stunted, and dying okra plants were observed in a 50-acre field in Homestead, FL, U.S.A. Three isolates of microorganisms associated with symptomatic plants were obtained and identified as Pythium aphanidermatum based on the morphological characteristics and DNA sequencing. Phylogenetic analysis based on ITS, CoxII, and beta-tubulin sequences confirmed the identification. The pathogenicity of the Pythium isolates was confirmed on okra, revealing a high mortality rate up to 60 and 2.5% for pre- and postemergence damping off, respectively. This is the first report of P. aphanidermatum causing severe damping-off of okra in Florida and may pose a serious threat to okra production in Florida if not managed properly.
Phytophthora cinnamomi is a globally important soilborne Oomycete plant pathogen with an extensive and diverse host range, including numerous tree species and woody ornamental plants, and has disrupted forest ecosystems on multiple continents. Members of the Gordonieae tribe, in the family Theaceae, exhibit varying degrees of susceptibility to P. cinnamomi, with Franklinia alatamaha likely being extinct in nature because it is very susceptible to this pathogen. In contrast, Gordonia lasianthus, or loblolly bay, was previously considered resistant when compared with other Gordonieae species. However, in 2019, bleeding cankers were observed on the lower trunk of mature G. lasianthus trees in a coastal forest in South Carolina, in an area that experienced extensive flooding, likely due to a recent hurricane and anthropogenic development. This study demonstrates how prolonged exposure to flooded soil conditions significantly increased susceptibility of G. lasianthus to P. cinnamomi and led to severe symptoms of wilting, defoliation, and mortality. It also suggests how host-pathogen interactions involving species of Phytophthora may shift in the future because of climate change and increased frequency of extreme weather events.
Stubby root nematodes (SRN) are plant-parasitic nematodes known to cause damage to a wide range of crops, including blueberries. However, while blueberries are native to the eastern and northern regions of the United States, no information is available regarding the presence or distribution of SRN in blueberry production systems in Pennsylvania. To address this gap, between 2023 to 2025, a statewide survey was conducted to assess plant-parasitic nematode populations in commercial blueberry fields in the state. The survey detected the SRN Nanidorus renifer (syn. Paratrichodorus renifer) in 50% of the surveyed counties, at densities of 4 to 56 SRN/100 cm3 of soil. Subsequent sampling also confirmed the occurrence of this species in wild blueberry plants within the state. These findings represent the first report of N. renifer in the rhizosphere of both cultivated and wild blueberry plants in Pennsylvania.
