scholarly journals Investigating Phenylamide Insensitivity in Wisconsin Populations of Pseudoperonospora humuli

2019 ◽  
Vol 20 (4) ◽  
pp. 263-269
Author(s):  
Michelle E. Marks ◽  
Amanda J. Gevens
Keyword(s):  
High Risk ◽  
Disease Control ◽  
Downy Mildew ◽  
Systemic Disease ◽  
Leaf Disk ◽  
Crop Response ◽  
Varietal Resistance ◽  
Pseudoperonospora Humuli ◽  
Highly Effective

Hop downy mildew caused by the oomycete Pseudoperonospora humuli is primarily managed with fungicides because commercial varietal resistance is unavailable. Mefenoxam, a phenylamide-class fungicide, is highly effective for systemic disease control but is at high risk for the development of pathogen insensitivity. Due to the recent expansion of hop production in Wisconsin, it was unknown if P. humuli could be managed with mefenoxam because insensitivity has been documented in other regions. During 2015 to 2017, isolates of P. humuli were collected from commercial yards throughout Wisconsin. Isolates were screened for insensitivity using a leaf disk assay with fungicide-amended water agar. Insensitivity was determined using a single discriminatory dose of 25 μg/ml of mefenoxam, and isolates were considered insensitive if they exhibited at least 50% sporulation on amended media relative to nonamended water agar. Over all years, nearly 48% of all isolates were insensitive to mefenoxam. The incidence of insensitivity varied between individual hop yards, with most yards exhibiting a mixture of sensitive and insensitive isolates. At this time, mefenoxam-insensitive populations do not appear to be predominant in Wisconsin. Growers should monitor the effectiveness of mefenoxam applications in their hop yards and be responsive to changes in crop response.

scholarly journals Pre- and Postinfection Activity of Fungicides in Control of Hop Downy Mildew

Plant Disease ◽  
2015 ◽  
Vol 99 (6) ◽  
pp. 858-865 ◽  
Author(s):  
David H. Gent ◽  
Megan C. Twomey ◽  
Sierra N. Wolfenbarger ◽  
Joanna L. Woods
Keyword(s):  
Disease Control ◽  
Downy Mildew ◽  
Field Experiments ◽  
Resistance Management ◽  
Field Studies ◽  
Similar Efficacy ◽  
Application Timing ◽  
Pseudoperonospora Humuli ◽  
Hazard Warnings ◽  
Post Hoc

Optimum timing and use of fungicides for disease control are improved by an understanding of the characteristics of fungicide physical mode of action. Greenhouse and field experiments were conducted to quantify and model the duration of pre- and postinfection activity of fungicides most commonly used for control of hop downy mildew (caused by Pseudoperonospora humuli). In greenhouse experiments, control of downy mildew on leaves was similar among fungicides tested when applied preventatively but varied depending on both the fungicide and the timing of application postinfection. Disease control decreased as applications of copper were made later after inoculation. In contrast, cymoxanil, trifloxystrobin, and dimethomorph reduced disease with similar efficacy when applied 48 h after inoculation compared with preventative applications of these fungicides. When fungicides were applied 72 h after inoculation, only dimethomorph reduced the sporulating leaf area similarly to preinoculation application timing. Adaxial chlorosis, necrosis, and water soaking of inoculated leaves, indicative of infection by P. humuli, were more severe when plants were treated with cymoxanil, trifloxystrobin, and dimethomorph 48 to 72 h after inoculation, even though sporulation was suppressed. Trifloxystrobin and dimethomorph applied 72 h after inoculation suppressed formation of sporangia on sporangiophores as compared with all other treatments. In field studies, dimethomorph, fosetyl-Al, and trifloxystrobin suppressed development of shoots with systemic downy mildew to the greatest extent when applied near the timing of inoculation, although the duration of preventative and postinfection activity varied among the fungicides. There was a small reduction in efficacy of disease control when fosetyl-Al was applied 6 to 7 days after inoculation as compared with protective applications. Trifloxystrobin had 4 to 5 days of preinfection activity and limited postinfection activity. Dimethomorph had the longest duration of protective activity. Percent disease control was reduced progressively with increasing time between inoculation and application of dimethomorph. These findings provide guidance to the use of fungicides when applications are timed with forecasted or post hoc disease hazard warnings, as well as guidance on tank-mixes of fungicides that may be suitable both for resistance management considerations and extending intervals between applications.

scholarly journals High Levels of Insensitivity to Phosphonate Fungicides in Pseudoperonospora humuli

Plant Disease ◽  
2020 ◽  
Vol 104 (5) ◽  
pp. 1400-1406 ◽  
Author(s):  
David H. Gent ◽  
Mary Block ◽  
Briana J. Claassen
Keyword(s):  
Disease Control ◽  
Downy Mildew ◽  
Plant Pathogens ◽  
Phosphorous Acid ◽  
Rate Sensitivity ◽  
Field Studies ◽  
Planting Material ◽  
Pseudoperonospora Humuli ◽  
Action Committee ◽  
Allowable Rate

Phosphonate (phosphite; HPO3−2) is fungicidal against oomycetes and certain other organisms. The Fungicide Resistance Action Committee has deemed phosphonate to be at low risk of resistance development, and reduced sensitivity to phosphonate has been reported only occasionally in plant pathogens. Reduced sensitivity to the fungicide fosetyl-Al was documented in the hop downy mildew pathogen, Pseudoperonospora humuli, in the early 2000s, but disease caused by insensitive isolates could still be managed commercially if the fungicide rate was doubled from 2.24 to 4.48 kg/ha. In this research, we document the occurrence of isolates of P. humuli in Oregon that possess even higher levels of insensitivity to fosetyl-Al and other phosphonate fungicides. The median estimated effective concentration required to reduce infection by 50% (EC50) for isolates collected from two farms reporting disease control failures was 2.7% (vol/vol) phosphonate (range = 1.6 to 164.2), which was 1.6 times (range = 0.9 to 96.0) the maximum labeled rate of the phosphonate fungicide utilized. In contrast, the median EC50 for isolates obtained from experimental plots that have received only a single application of a phosphonate fungicide was 0.6% (vol/vol) phosphonate (range = 0.11 to 2.3) or 0.3 times the maximum allowable rate. Sensitivity of isolates to a phosphorous acid fungicide, fosetyl-Al, and a plant nutrient product containing an unspecified level of phosphorous acid were linearly related. Insensitivity to the maximum allowable rate of a phosphorous acid fungicide was widespread within and among hop farms in Oregon. Among 54 isolates assayed for phosphonate insensitivity, 96% had EC50 values that exceeded the maximum allow rate of the fungicide used in the assays. Field studies conducted in 2 years further demonstrated that a phosphorous fungicide, a nutrient product containing phosphorous acid, and fosetyl-Al failed to provide commercially acceptable suppression of downy mildew when applied at the maximum allowable rates and even double these rates, whereas fungicides with different modes of action provided 91% or greater disease control. The whole of this research indicates that P. humuli has been selected to tolerate fosetyl-Al and other phosphonate fungicides at rates four times greater than those used earlier to obtain satisfactory suppression of downy mildew. This finding has implications for management of the disease not only in Oregon but also, in other production regions should insensitive isolates be introduced on infected planting material.

Sensitivity of Pseudoperonospora humuli (the Causal Agent of Hop Downy Mildew) from Oregon, Idaho, and Washington to Fosetyl-Al (Aliette)

2004 ◽  
Vol 5 (1) ◽  
pp. 4 ◽  
Author(s):  
Mark E. Nelson ◽  
Kenneth C. Eastwell ◽  
Gary G. Grove ◽  
James D. Barbour ◽  
Cynthia M. Ocamb ◽  
...  
Keyword(s):  
Downy Mildew ◽  
Dose Response ◽  
Humulus Lupulus ◽  
Leaf Disk ◽  
Causal Agent ◽  
Response Curves ◽  
Pseudoperonospora Humuli ◽  
Dose Response Curves ◽  
Northern Idaho

Failures of fosetyl-Al (Aliette) to control hop (Humulus lupulus) downy mildew, caused by Pseudoperonospora humuli, have recently occurred in northern Idaho and Oregon. To determine if resistance of the pathogen to the fungicide has developed, leaf disk assays were conducted to compare sensitivity of P. humuli isolates from the different U.S. hop-growing regions to isolates from a research yard where exposure to fosetyl-Al had not occurred for at least 10 years. Dose response curves of transformed data were linear. The fosetyl-Al concentration effective against 50% of the P. humuli isolates (ED50) from each location was estimated from the linearized data. The ED50 values indicate that fosetyl-Al was about one-third as effective against P. humuli isolates from commercial hop yards in northern Idaho and Oregon and about one-half as effective against isolates from southern Idaho compared to isolates from the research yard. Commercial yards in Washington were similar to the research yard. Accepted for publication 3 August 2004. Published 11 August 2004.

scholarly journals The hop downy mildew pathogen Pseudoperonospora humuli

2021 ◽  
Author(s):  
Savithri Purayannur ◽  
David H. Gent ◽  
Timothy D. Miles ◽  
Sebastjan Radišek ◽  
Lina M. Quesada‐Ocampo
Keyword(s):  
Downy Mildew ◽  
Pseudoperonospora Humuli

Preeclampsia Part 2: fisiopatologia e trattamento

2019 ◽  
Vol 31 (2) ◽  
pp. 79-88
Author(s):  
Stefano Michelassi
Keyword(s):  
High Risk ◽  
Endothelial Dysfunction ◽  
Preterm Delivery ◽  
Systemic Inflammation ◽  
Systemic Disease ◽  
Clinical Manifestations ◽  
Morbidity And Mortality ◽  
Curative Treatment ◽  
Maternal Risks ◽  
New Onset

Preeclampsia is a pregnancy-specific disorder usually defined as new-onset hypertension and proteinuria after the 20th week of gestation. Preeclampsia is a systemic disease with multiorgan involvement, and it is associated with a high risk of maternal and fetal morbidity and mortality. To date its pathogenesis is not completely understood, but placental hypoxia or hypoxia/reoxigenation may be the basic condition leading to systemic inflammation and endothelial dysfunction that induce all the clinical manifestations of the disorder. Delivery is the only curative treatment. Indeed, for the management of preeclampsia one needs to consider both the maternal risks due to continued pregnancy and the fetal risks associated with induced preterm delivery.

Transplantation of Center for Disease Control “High-Risk” Donor Hearts Does Not Adversely Impact Long-Term Outcomes in Adults

2016 ◽  
Vol 22 (5) ◽  
pp. 376-382 ◽  
Author(s):  
Ann C. Gaffey ◽  
Andrew J. Cucchiara ◽  
Lee R. Goldberg ◽  
Emily A. Blumberg ◽  
Michael A. Acker ◽  
...  
Keyword(s):  
High Risk ◽  
Disease Control ◽  
Long Term Outcomes

scholarly journals Can High-Risk Fungicides be Used in Mixtures Without Selecting for Fungicide Resistance?

2014 ◽  
Vol 104 (4) ◽  
pp. 324-331 ◽  
Author(s):  
Alexey Mikaberidze ◽  
Bruce A. McDonald ◽  
Sebastian Bonhoeffer
Keyword(s):  
High Risk ◽  
Disease Control ◽  
Fungicide Resistance ◽  
Fungal Pathogens ◽  
Development Of Resistance ◽  
Population Dynamics Model ◽  
Fungicide Mixtures ◽  
Cost Of Resistance ◽  
Selection For ◽  
Crucial Parameter

Fungicide mixtures produced by the agrochemical industry often contain low-risk fungicides, to which fungal pathogens are fully sensitive, together with high-risk fungicides known to be prone to fungicide resistance. Can these mixtures provide adequate disease control while minimizing the risk for the development of resistance? We present a population dynamics model to address this question. We found that the fitness cost of resistance is a crucial parameter to determine the outcome of competition between the sensitive and resistant pathogen strains and to assess the usefulness of a mixture. If fitness costs are absent, then the use of the high-risk fungicide in a mixture selects for resistance and the fungicide eventually becomes nonfunctional. If there is a cost of resistance, then an optimal ratio of fungicides in the mixture can be found, at which selection for resistance is expected to vanish and the level of disease control can be optimized.

scholarly journals Using Epidemiological Principles to Explain Fungicide Resistance Management Tactics: Why do Mixtures Outperform Alternations?

2018 ◽  
Vol 108 (7) ◽  
pp. 803-817 ◽  
Author(s):  
James A. D. Elderfield ◽  
Francisco J. Lopez-Ruiz ◽  
Frank van den Bosch ◽  
Nik J. Cunniffe
Keyword(s):  
High Risk ◽  
Disease Control ◽  
Fungicide Resistance ◽  
Total Yield ◽  
Resistance Management ◽  
Careful Consideration ◽  
Low Risk ◽  
Model Parameterization ◽  
Grapevine Powdery Mildew ◽  
Label Dose

Whether fungicide resistance management is optimized by spraying chemicals with different modes of action as a mixture (i.e., simultaneously) or in alternation (i.e., sequentially) has been studied by experimenters and modelers for decades. However, results have been inconclusive. We use previously parameterized and validated mathematical models of wheat Septoria leaf blotch and grapevine powdery mildew to test which tactic provides better resistance management, using the total yield before resistance causes disease control to become economically ineffective (“lifetime yield”) to measure effectiveness. We focus on tactics involving the combination of a low-risk and a high-risk fungicide, and the case in which resistance to the high-risk chemical is complete (i.e., in which there is no partial resistance). Lifetime yield is then optimized by spraying as much low-risk fungicide as is permitted, combined with slightly more high-risk fungicide than needed for acceptable initial disease control, applying these fungicides as a mixture. That mixture rather than alternation gives better performance is invariant to model parameterization and structure, as well as the pathosystem in question. However, if comparison focuses on other metrics, e.g., lifetime yield at full label dose, either mixture or alternation can be optimal. Our work shows how epidemiological principles can explain the evolution of fungicide resistance, and also highlights a theoretical framework to address the question of whether mixture or alternation provides better resistance management. It also demonstrates that precisely how spray tactics are compared must be given careful consideration.[Formula: see text] Copyright © 2018 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

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