Management of Powdery Mildew on Ninebark Using Sanitizers, Biorational Products, and Fungicides

Ninebark (Physocarpus opulifolius) is a popular ornamental shrub and considered a hardy and tough plant that can thrive in different environmental conditions and resist diseases. However, powdery mildew, caused by Podosphaera physocarpi, can severelyaffect ninebark, deteriorating the ornamental value and making them unmarketable. Only a few studies have been done in managing powdery mildew of ninebark. The current study focuses on evaluating and identifying effective products (sanitizers, biorational products, and fungicides) for the management of powdery mildew disease of ninebark. A total of 12 treatments, including nontreated control, were studied. The experiment was arranged in randomized complete block design with four-single ‘Mindia Coppertina®’ ninebark plant per treatment and repeated twice. Powdery mildew disease severity, growth parameters, and phytotoxicity were assessed in the study. All treatments significantly reduced the powdery mildew disease severity and disease progress [area under disease progress curve (AUDPC)] compared with the nontreated control. The treatments, such as azoxystrobin + benzovindiflupyr at 0.17 and 0.23 g·L–1 total active ingredients (a.i.) applied, chlorothalonil + propiconazole at 1.12 mL·L–1 total a.i. applied, azoxystrobin + tebuconazole at 0.11 and 0.16 g·L–1 total a.i. applied, and giant knotweed extract [Reynoutria sachalinensis (0.5 mL·L–1 total a.i. applied)] were the most effective treatments in reducing disease severity and disease progress in both trials. The treatments had no significant effects on the plant growth parameters such as height and width. In Expt. 2, azoxystrobin + benzovindiflupyr and hydrogen peroxide + peroxyacetic acid treated plants showed the low level of phytotoxic symptoms. The phytotoxicity of these two treatments in Expt. 2 could be related to higher environmental temperature during the experimental period

Identification of Fusarium commune, the Causal Agent of Postharvest Zinnia Meltdown Disease in Tennessee

The cut flower growers of the eastern and southern United States are threatened with postharvest meltdown of zinnia (Zinnia elegans), which reduces yield and income as well as limiting opportunities for production expansion. Disease symptoms such as bending of the stem just below the flower were visually apparent on zinnia cut flowers. The objective of this study was to identify the causal agent related to zinnia meltdown. A total of 20 symptomatic zinnia cut flower stems were collected from Tennessee. Several Fusarium-like colonies with micro and macroconidia were isolated from the base and bend area of stems on potato dextrose agar (PDA) and Fusarium-selective media. Morphological characterization, polymerase chain reaction, and sequencing of three representative isolates, FBG2020_198, FBG2020_199, and FBG2020_201, were conducted to confirm pathogen identification. The sequence identity of the isolates was \u3e99% identical to Fusarium commune, and a combined phylogenetic tree grouped the isolates with the clade of F. commune from different host and geographical locations. To accomplish Koch’s postulates, a pathogenicity test was performed on ‘Benary’s Giant Golden Yellow’, ‘Benary’s Giant Lime’, and ‘Benary’s Giant Pink’ zinnia plants at vegetative (2 weeks after transplantation) or flower bud stage (1 month after transplantation) by drench, stem injection, and foliar spray of conidial suspension (1 × 105 conidia/mL). Similar symptoms of meltdown (floral axis bending just below the flower) were observed on inoculated zinnia cultivars 2 days after harvesting. Fusarium commune was re-isolated from the infected flower stems of all three cultivars but not from the noninoculated zinnia flower stems. Zinnia stem colonization by F. commune was statistically similar in all three tested cultivars regardless of plant growth stage and method of inoculation. This study confirms F. commune as being the causal agent of postharvest zinnia flower meltdown issue in Tennessee. In the future, possible sources of pathogen will be screened, and disease management recommendations will be developed

Genome assembly and visualization of aggressive wheat blast strain 16MoT01

Wheat blast, a highly destructive fungal disease caused by pathotype Magnaporthe oryzae Triticum, can cause up to 100% yield loss in wheat fields under optimal pathogen conditions. Until 2016, the disease had been confined to South America, but recent outbreaks of the disease in Asia and Africa threaten the global wheat supply. This study aims to characterize the genome structure of strain 16MoT01, which has proven to be particularly aggressive even towards wheat genotypes that have previously been resistant to blast. Genomic DNA from 16MoT01 was sequenced using Oxford Nanopore long read sequencing, assembled with Canu, and polished using Illumina reads, resulting in a finished chromosome-level assembly consisting of seven core-chromosomes, a mini-chromosome, and a mitochondrial genome. When compared to the reference genome of strain B71, the core-chromosomes show high similarity and the mini-chromosome shows a high level of divergence. The presence of mini-chromosomes will be confirmed through contour-clamped electric field (CHEF) gel electrophoresis. The CHEF protocol was developed using genomic DNA from a rice blast fungus. This assembly provides another reference genome and potential insights into what makes this strain so aggressive

Comparative Performance of Reduced-risk Fungicides and Biorational Products in Management of Postharvest Botrytis Blight on Bigleaf Hydrangea Cut Flowers

Botrytis cinerea is one of the problematic and notorious postharvest pathogens of bigleaf hydrangea (Hydrangea macrophylla) cut flowers. It causes flower blight, leaf blight, and stem rot, reducing the ornamental value (such as longevity, color, and texture) of flowers, ultimately making them unsalable. The objective of this study was to identify effective conventional fungicides and biorational products for botrytis blight management on bigleaf hydrangea cut flowers that can be easily and readily adopted by growers of ornamentals. Preventive preharvest whole-plant spray and postharvest dip treatment applications were used in this study. For the whole-plant spray applications, bigleaf hydrangea plants were sprayed with treatment solution 3 days before harvesting flowers. For the dip applications, cut flowers were dipped in treatment solutions after harvest. For both application types, flowers were inoculated with B. cinerea spores once treatment solutions dried. Flowers were stored in cold storage for 3 days and then displayed in conditions similar to retail stores. Botrytis blight disease severity, marketability of flower (postharvest vase life), phytotoxicity, and application residue were assessed in the study. Treatments showed variable efficacy in managing postharvest B. cinerea infection in bigleaf hydrangea cut flowers. Preventive preharvest whole-plant spray and postharvest dip applications of isofetamid and fluxapyroxad + pyraclostrobin significantly reduced the postharvest botrytis blight disease severity and area under disease progress curve (AUDPC) compared with the positive control (nontreated, inoculated with B. cinerea). When applied as a postharvest dip, the fungicide fludioxonil and biofungicide Aureobasidium pullulans strains DSM 14940 and DSM 14941 effectively lowered the disease severity and disease progress (AUDPC). These effective treatments also maintained a significantly longer postharvest vase life of bigleaf hydrangea cut flowers compared with the nontreated, inoculated control. The longer vase life may be attributed to lowered botrytis blight disease severity and the resultant proper physiological functioning of flowers

First Report of Powdery Mildew on Physocarpus opulifolius Caused by Podosphaera physocarpi in Tennessee

Eastern ninebark (Physocarpus opulifolius [L.] Maxim.) is a popular native perennial plant used in landscapes because of its colorful foliage and spring flower display. Powdery mildew symptoms were observed on container-grown eastern ninebark ‘Mindia’ Coppertina plants in a commercial nursery in DeKalb County, TN, in May 2016. The disease severity was nearly 40%, and the disease incidence was nearly 60% of 1,000 plants. Affected plants displayed witches’ brooms with cream to white colored, thickened shoots with stunted, curly leaves as well as patches of white powdery fungal growth on the surface of young and old leaves, inflorescences, infructescences, and stems. Microscopic observation revealed masses of conidia and mycelium covering symptomatic tissues. Conidiophore foot cells measured 19.2 to 66.7 μm (mean = 38.3 μm) × 5.4 to 15.1 μm (mean = 9.7 μm) (n = 30). Conidia were ovoid and measured 11.4 to 28.5 μm (mean = 20.9 μm) (n = 30) in length and 8.2 to 14.8 μm (mean = 11.7 μm) (n = 30) in width. Conidiophores produced two to six conidia in chains. Fibrosin bodies were observed after treating conidia with a 3% KOH solution. Chasmothecia were numerous, 60.0 to 85.0 μm (mean = 74.2 μm) (n = 30) in size and contained one ascus (60.0 to 82.0 × 52.0 to 69.0 μm; mean = 73.4 × 59.4 μm [n = 30]) with eight ascospores (25.2 to 28.0 × 14.8 to 16.0 μm; mean = 26.5 × 15.5 μm [n = 30]). To confirm pathogen identity, total DNA was extracted directly from plant tissue with the UltraClean Microbial DNA Isolation Kit (MO BIO Laboratories, Carlsbad, CA) following the manufacturer’s instructions. The internal transcribed spacer region of the ribosomal DNA was amplified by polymerase chain reaction (PCR) using primer pair ITS1 and ITS4 (White et al. 1990). The sequence (GenBank accession no. MT605142) of the amplicon had 100% coverage and 100% identity to that of Podosphaera physocarpi (U. Braun) U. Braun (= Podosphaera aphanis var. physocarpi [U. Braun] U. Braun & S. Takam.) (GenBank accession no. MT106654). Pathogenicity was confirmed three times by inoculating leaf surfaces of five eastern ninebark Mindia Coppertina plants by tapping fungal spores from infected eastern ninebark leaves onto the surfaces of healthy leaves. Inoculated plants were maintained in a greenhouse (21 to 23°C) using a drip irrigation system until symptoms developed. Five noninoculated control plants were maintained in the same greenhouse. After 2 weeks, typical symptoms of powdery mildew developed on the inoculated plants, and microscopic examination revealed the same pathogen morphology as the original isolate. All noninoculated control plants remained disease-free. To our knowledge, this is the first report of powdery mildew caused by P. physocarpi on P. opulifolius in Tennessee. Powdery mildew is known to be a disease problem on eastern ninebark grown in its native range in landscape plantings. Lubell et al. (2011) reported varying levels of powdery mildew resistance among eastern ninebark cultivars. Timely application of fungicides with no phytotoxic effect will be necessary to manage this disease on susceptible eastern ninebark cultivars in affected nurseries

Integration of Sanitation Practices and Fungicide Applications for Assuring Better Postharvest Shelf Life of Cut Flowers and Greenery

Botrytis blight, boxwood blight and Volutella blight caused by Botrytis cinerea Pers. Fr. [teleomorph Botryotinia fuckeliana (de Bary) Whetzel], Calonectria pseudonaviculata Lombard, Wingf, & Crous, and Pseudonectria foliicola Lambard & Crous, respectively are becoming more problematic in ornamental plant production, reducing the quantity, quality, and marketability of susceptible plants. These pathogens can be mechanically transmitted through air, water splash, cutting tools and equipment, worker gloves, shoes, and clothes. These pathogens can cause disease in ornamental plants in both field and postharvest conditions. Sometimes, these pathogens remain inactive during harvesting of ornamental flowers or greenery, but cause infection during transportation, storage, and retail/wholesale shop. These pathogens not only affect the plants but also cause significant loss in postharvest life of cut flowers and greenery. The objective of this study was to evaluate the efficacy of sanitizers, biorational products, and fungicides in managing the pre and postharvest foliar diseases of cut flowers and greenery. In this current study, isofetamid, fluxapyroxad + pyraclostrobin, and biofungicide Aureobasidium pullulans strain DSM 14940 and DSM 14941 were the most effective treatments in reducing the postharvest botrytis blight on bigleaf hydrangea cut flowers. Similarly, (ODD + DoD + DdD + DB)AC [Simple Green D Pro 5], 2 propanol + DDAC [0.12% (KleenGrow)], and DBAC + DEAC [GreenShield] were the most effective in reducing the plant to plant transfer of boxwood blight and Volutella blight when pruned with contaminated Felco 19 shears. In addition to the three effective treatments above, acetic acid [2.5% (Vinegar)], 2-propanol + DDAC (0.06%), sodium hypochlorite [Clorox] and potassium peroxymonosulfate + NaCl [2% (Virkon)] were effective in reducing postharvest boxwood blight whereas DBAC + DBAC [Lysol All-purpose Cleaner], ethanol [70% (Ethyl alcohol)] and DDAC +DBAC [Simple Green D Pro 3 plus] were effective in reducing Volutella blight disease severity, AUDPC, and maintained better quality and longer postharvest shelf life of boxwood cuttings. Additionally, we also identified the causal agent for bending (meltdown) of zinnia cut flower stem. The morphological, molecular, and phylogenetic analysis, as well as pathogenicity test, determined that Fusarium commune Skovgaard, Rosendahl, O’Donnell & Nirenberg is the causal agent of zinnia meltdown in Tennessee

Management of Powdery Mildew on Ninebark Using Sanitizers, Biorational Products, and Fungicides

Ninebark (Physocarpus opulifolius) is a popular ornamental shrub and considered a hardy and tough plant that can thrive in different environmental conditions and resist diseases. However, powdery mildew, caused by Podosphaera physocarpi, can severelyaffect ninebark, deteriorating the ornamental value and making them unmarketable. Only a few studies have been done in managing powdery mildew of ninebark. The current study focuses on evaluating and identifying effective products (sanitizers, biorational products, and fungicides) for the management of powdery mildew disease of ninebark. A total of 12 treatments, including nontreated control, were studied. The experiment was arranged in randomized complete block design with four-single ‘Mindia Coppertina®’ ninebark plant per treatment and repeated twice. Powdery mildew disease severity, growth parameters, and phytotoxicity were assessed in the study. All treatments significantly reduced the powdery mildew disease severity and disease progress [area under disease progress curve (AUDPC)] compared with the nontreated control. The treatments, such as azoxystrobin + benzovindiflupyr at 0.17 and 0.23 g·L–1 total active ingredients (a.i.) applied, chlorothalonil + propiconazole at 1.12 mL·L–1 total a.i. applied, azoxystrobin + tebuconazole at 0.11 and 0.16 g·L–1 total a.i. applied, and giant knotweed extract [Reynoutria sachalinensis (0.5 mL·L–1 total a.i. applied)] were the most effective treatments in reducing disease severity and disease progress in both trials. The treatments had no significant effects on the plant growth parameters such as height and width. In Expt. 2, azoxystrobin + benzovindiflupyr and hydrogen peroxide + peroxyacetic acid treated plants showed the low level of phytotoxic symptoms. The phytotoxicity of these two treatments in Expt. 2 could be related to higher environmental temperature during the experimental period

Comparative Performance of Reduced-risk Fungicides and Biorational Products in Management of Postharvest Botrytis Blight on Bigleaf Hydrangea Cut Flowers

Botrytis cinerea is one of the problematic and notorious postharvest pathogens of bigleaf hydrangea (Hydrangea macrophylla) cut flowers. It causes flower blight, leaf blight, and stem rot, reducing the ornamental value (such as longevity, color, and texture) of flowers, ultimately making them unsalable. The objective of this study was to identify effective conventional fungicides and biorational products for botrytis blight management on bigleaf hydrangea cut flowers that can be easily and readily adopted by growers of ornamentals. Preventive preharvest whole-plant spray and postharvest dip treatment applications were used in this study. For the whole-plant spray applications, bigleaf hydrangea plants were sprayed with treatment solution 3 days before harvesting flowers. For the dip applications, cut flowers were dipped in treatment solutions after harvest. For both application types, flowers were inoculated with B. cinerea spores once treatment solutions dried. Flowers were stored in cold storage for 3 days and then displayed in conditions similar to retail stores. Botrytis blight disease severity, marketability of flower (postharvest vase life), phytotoxicity, and application residue were assessed in the study. Treatments showed variable efficacy in managing postharvest B. cinerea infection in bigleaf hydrangea cut flowers. Preventive preharvest whole-plant spray and postharvest dip applications of isofetamid and fluxapyroxad + pyraclostrobin significantly reduced the postharvest botrytis blight disease severity and area under disease progress curve (AUDPC) compared with the positive control (nontreated, inoculated with B. cinerea). When applied as a postharvest dip, the fungicide fludioxonil and biofungicide Aureobasidium pullulans strains DSM 14940 and DSM 14941 effectively lowered the disease severity and disease progress (AUDPC). These effective treatments also maintained a significantly longer postharvest vase life of bigleaf hydrangea cut flowers compared with the nontreated, inoculated control. The longer vase life may be attributed to lowered botrytis blight disease severity and the resultant proper physiological functioning of flowers

Identification and Management of Phytophthora Aerial Blight Caused by Phytophthora nicotianae on Catharanthus roseus

Phytophthora nicotianae is the most common pathogen in nurseries and gardens, infecting both woody and herbaceous ornamental plants. Phytophthora aerial blight symptoms such dull water-soaked lesions on shoot tips and leaf petioles, girdling on the main stem, necrosis, and wilting of annual vinca were observed in a commercial greenhouse in Warren Co., Tennessee, USA in May 2016. The objective of this study was to identify the causal agent of Phytophthora aerial blight and develop a fungicide management recommendation for ornamental producers. Attempts to isolate the pathogen from symptomatic leaf tissue were conducted and excised leaf pieces were embedded in the V8 agar medium. Morphological characterization, polymerase chain reaction (PCR), sequencing, and pathogenicity test of the isolate FBG2016_444 were conducted to confirm the pathogen identification. The sequence identity was 100% identical to Phytophthora nicotianae, and a combined phylogenetic tree (internal transcribed spacer [ITS]), the large subunit [LSU] of rDNA, and ras-related protein gene [Ypt1]) grouped isolate FBG2016_444 within the clade of P. nicotianae. In the pathogenecity study, all inoculated annual vinca plant showed the Phytophthora aerial blight symptoms and P. nicotianae was re-isolated whereas non-inoculated annual vinca plant remained symptomless. These findings confirmed P. nicotianae as the causal agent of Phytophthora aerial blight of annual vinca. In addition, two rates (0.078 and 0.156 mL·L-1) and three application intervals (7, 14 and 21 days before inoculation [DBI]) of oxathiapiprolin (Segovis®) were evaluated for their ability to reduce the Phytophthora aerial blight severity on annual vinca plants. The control groups were positive (non-treated inoculated) and negative (non-treated non-inoculated) plants. Both rates and application timings of oxathiapiprolin significantly reduced Phytophthora aerial blight severity and disease progress (area under disease progress curve [AUDPC]) on annual vinca plants compared to the positive control. However, 0.078 and 0.156 mL·L-1 of oxathiapiprolin applied at 7 or 14 DBI were the most effective treatments in reducing the disease severity and AUDPC on annual vinca plants. The plant growth parameters such as increase in height and width, total plant weight, and root weight were not influenced by the application of oxathiapiprolin. The finding reported in this study will help ornamental growers with better management of Phytophthora aerial blight of annual vinca

Comparative Performance of Chemical and Biological-based Products in Management of Algal Leaf Spot on Magnolia

Magnolia trees (Magnolia sp.) are a popular choice for consumers when choosing flowering woody plants for landscapes. Magnolia species grow in a wide variety of both temperate and tropical locations. Southern magnolia (Magnolia grandiflora) is one of the more popular magnolias due to its pleasing aesthetics: large showy flowers in a range of colors and evergreen foliage. However, magnolias can be affected by algal leaf spot. Algal leaf spot is caused by Cephaleuros virescens, which is a widespread plant parasitic green alga. There has been little research on how to treat algal leaf spot on magnolia plants. This study focuses on identifying effective biological- and chemical-based fungicides for the management of algal leaf spot disease of magnolia plants. Two experiments were conducted in a randomized complete block design with six replications per treatment and a total of 12 treatments, including a nontreated control. The first experiment (Expt. 1) was conducted in a shade house (56% shade) at McMinnville, TN, using southern magnolia plants. The second experiment (Expt. 2) was conducted at a commercial nursery in McMinnvillle, TN, in a field plot planted with ‘Jane’ magnolia (Magnolia liliiflora ‘Nigra’ × Magnolia stellata ‘Rosea’). The algal leaf spot disease severity, disease progression, plant marketability and growth parameters were evaluated. In both experiments, all treatments reduced algal leaf spot disease severity and disease progress in comparison with the nontreated control. In Expt. 1, copper octanoate, copper oxychloride, chlorothalonil water-dispersible granules, chlorothalonil suspension concentrate, didecyl dimethyl ammonium chloride, azoxystrobin + benzovindiflupyr, hydrogen peroxide + peroxyacetic acid, and mono- and di-potassium salts of phosphorus acid + hydrogen peroxide reduced the disease severity and disease progress the most and were not statistically different from one another. In Expt. 2, azoxystrobin + benzovindiflupyr, didecyl dimethyl ammonium chloride, and copper oxychloride significantly reduced disease severity and disease progress (area under disease progress curve). Treatments had no deleterious effect on plant growth parameters such as height and width, and no phytotoxicity of applied treatments or defoliation was observed. Treated magnolia plants had better plant marketability compared with the nontreated control plants. The findings of this study will help growers to achieve better management of algal leaf spot disease on magnolia trees