scholarly journals Prevalence of Myclobutanil Resistance and Difenoconazole Insensitivity in Populations of Venturia inaequalis

Plant Disease ◽  
2015 ◽  
Vol 99 (11) ◽  
pp. 1526-1536 ◽  
Author(s):  
Sara M. Villani ◽  
Alan R. Biggs ◽  
Daniel R. Cooley ◽  
Jessica J. Raes ◽  
Kerik D. Cox
Keyword(s):  
New England ◽  
Field Experiments ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Apple Fruit ◽  
Scab Control ◽  
Dmi Fungicides ◽  
Commercial Research ◽  
Mature Apple ◽  
Single Lesion

Demethylation inhibitors (DMIs) are a class of single-site fungicides with high levels of protective and curative efficacy against Venturia inaequalis, the causal agent of apple scab. To determine the prevalence of resistance to the DMI fungicide myclobutanil, 3,987 single-lesion conidial V. inaequalis isolates from 141 commercial, research, and baseline orchard populations were examined throughout New England, the mid-Atlantic, and the Midwest from 2004 to 2013. Of these orchard populations, 63% had practical resistance, 13% had reduced sensitivity, and 24% were sensitive to myclobutanil. A sensitivity baseline for the recently introduced DMI fungicide difenoconazole was established to make comparisons with myclobutanil sensitivity in orchard populations. The mean effective concentration of difenoconazole at which mycelial growth was inhibited by 50% (EC50) was determined to be 0.002 μg ml−1 for 44 baseline isolates of V. inaequalis. From 2010 to 2013, 1,012 isolates of V. inaequalis from 37 of the 141 orchard populations above were screened for sensitivity to difenoconazole. In all, 1 orchard population had reduced sensitivity to difenoconazole, while the remaining 36 orchard populations were sensitive to the fungicide. In field experiments, difenoconazole demonstrated high levels of apple scab control on mature apple fruit, despite the fact that the population of V. inaequalis had practical resistance to difenoconazole. Although our results indicate widespread resistance to myclobutanil but not difenoconazole, due to the propensity for cross-sensitivity among DMI fungicides, growers with myclobutanil resistance should be cautious when using difenoconazole for disease management.

scholarly journals Field comparison of sterol-biosynthesis-inhibiting fungicides used alone and in combination with protectant fungicides for apple scab control

2005 ◽  
Vol 71 (1) ◽  
pp. 1-8 ◽  
Author(s):  
J. Warner
Keyword(s):  
Disease Control ◽  
Broad Spectrum ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Field Trials ◽  
Sterol Biosynthesis ◽  
Scab Control

Several sterol-biosynthesis-inhibiting (SBI) fungicides were tested alone and in combination with a broad-spectrum protectant material in field trials for control of Venturia inaequalis. When used in a 10-day spray schedule, SBI fungicides, whether used alone or in a mixture, provided improved scab control as compared to the protectant material used alone. With bitertanol, diniconazole, and penconazole, the mixture also provided better scab control than when the SBI fungicide was used alone. However, with flusilazole and myclobutanil, no improvement in disease control occurred with the mixture as compared to the SBI fungicide alone. Fruit russeting was observed after a post-bloom application of hexaconazole and growth-regulating effects on the foliage were observed following cyproconazole and hexaconazole use. The use of SBI fungicides in mixtures to avoid or delay the development of fungus resistance is discussed.

scholarly journals Development of the antioxidant indexes (FRAP, TFC, TPC) of scabbing resistant apple varieties in storage

2020 ◽  
pp. 89-94
Author(s):  
Mihály Orosz-Tóth ◽  
Sándorné Kincses
Keyword(s):  
Nutritional Value ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Apple Fruit ◽  
Bioactive Substances ◽  
Total Polyphenol ◽  
Apple Variety ◽  
Apple Varieties ◽  
Apple Production ◽  
The Given

One of the most important groups of bioactive substances in apples are antioxidants, which have a health-preserving effect. The amount of these compounds varies not only during the ripening of the apple fruit, but also continuously during post-harvest storage. A growing group of health-conscious consumers are looking for apple varieties with a nutritional value that satisfies their needs. In the scope of our research, we examined 5 apple varieties originating from the Derecske horticultural site of KITE cPlc. in 2016. The plantation was planted to be suitable for intensive apple production. Samples were collected at the time of maturity (August-October) of the given variety. The 5 examined apple varieties (Gaia, Isaaq, Modí, Smeralda and Fujion) are all resistant to apple scab (fungal disease caused by Venturia inaequalis). The 2-month storage experiment was conducted at 16–17 °C, which had an aggressive effect on our stored apples. Total polyphenol (TPC) and flavonoid (TFC) content as well as FRAP values of the apples were measured. Measurements were taken immediately after harvest and after 1 and 2 months of storage. Our results were evaluated by using the IBM SPSS Statistics 20 software. Our aim was to compare the antioxidant results of 5 scab-resistant apple varieties, which change continuously during storage. The antioxidant content of our apple varieties increased during 2 months storage. The best result was achieved by the Modí apple variety (FRAP: 467.32 mg/100g; TFC: 317.76 mg/100g; TPC: 1771.97 mg/100g). Consumers may want to consume apples stored for a longer period of time if they are to absorb large amounts of antioxidants.

scholarly journals A new apple scab risk model that integrates ascospore release infection risk and susceptible leaf area

2004 ◽  
Vol 57 ◽  
pp. 20-24 ◽  
Author(s):  
R.M Beresford ◽  
W.R. Henshall ◽  
J.W. Palmer
Keyword(s):  
Leaf Area ◽  
Risk Model ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Black Spot ◽  
Infection Risk ◽  
Weather Data ◽  
Scab Control ◽  
Ascospore Release ◽  
Maturation Rate

A new model has been developed for assessing daytoday variation in risk of infection of apples by Venturia inaequalis the scab or black spot pathogen The model comprises three components ascospore availability wetnessbased infection risk based on Mills periods and susceptible leaf area The ascospore and wetnessbased infection risk components were adapted from previous models whereas the susceptible leaf area component is new When the model used weather data from Hawkes Bay and Nelson in spring 2003 the predicted risk incidence was determined mostly by wetnessbased infection risk but the magnitude of risk periods was greatly influenced by predicted ascospore release The susceptible leaf area component predicted a hitherto unidentified increase in infection risk after the peak in ascospore maturation rate had occurred The model is intended to assist in fungicide selection and timing for scab control in New Zealand apples but needs to be field tested before implementation

scholarly journals Effect of Sterol-demethylation Inhibiting Fungicides on Apple Fruit Set, Fruit Size, Total Yield, and Gross Returns

HortScience ◽  
2003 ◽  
Vol 38 (4) ◽  
pp. 601-604 ◽  
Author(s):  
D.A. Rosenberger ◽  
T.L. Robinson ◽  
J.R. Schupp ◽  
C.A. Engle-Ahlers ◽  
F.W. Meyer
Keyword(s):  
Plant Growth Regulator ◽  
Fruit Set ◽  
Total Yield ◽  
Apple Scab ◽  
Fruit Size ◽  
Apple Fruit ◽  
Fruit Weight ◽  
Dmi Fungicides ◽  
Apple Production ◽  
Fruit Size And Shape

Effects of three sterol-demethylation inhibiting (DMI) fungicides and a contact fungicide were compared over two years at each of two locations to determine if fungicide treatments had differential effects on productivity, fruit size and shape, or gross returns for `Empire' apples (Malus ×domestica Borkh.). Treatments were applied four to five times per year during the primary apple scab season. Effects of treatments were assessed by comparing fruit set efficiencies, number of fruit per tree, total harvested fruit weight, and fruit length: diameter ratios at harvest. No significant differences were noted among individual treatments in any of the four trials. However, when treatments were contrasted by grouping individual treatments, significantly larger fruit size was noted for triflumizole treatments vs. combined fenarimol and myclobutanil treatments in one of the four trials and for captan or mancozeb compared to fenarimol and myclobutanil treatments in two trials. None of the DMI fungicides compared in these trials had any consistent adverse affect on fruit size, total yield, or estimated gross return per hectare. We conclude that the plant growth regulator effects of DMI fungicides are inconsistent and are unlikely to have significant economic impact on commercial apple production.

Occurrence of QoI Resistance and Detection of the G143A Mutation in Michigan Populations of Venturia inaequalis

Plant Disease ◽  
2011 ◽  
Vol 95 (8) ◽  
pp. 927-934 ◽  
Author(s):  
Kimberley E. Lesniak ◽  
Tyre J. Proffer ◽  
Janna L. Beckerman ◽  
George W. Sundin
Keyword(s):  
Spore Germination ◽  
Control Strategies ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Pathogenic Fungi ◽  
Qoi Fungicides ◽  
Widespread Occurrence ◽  
Scab Control ◽  
High Level ◽  
Qoi Resistance

Control strategies for Venturia inaequalis rely heavily on chemical fungicides. Single-site fungicides such as the quinone-outside inhibitors (QoI) have been used in Michigan apple orchards for more than 11 years. In 2008, we sampled eight commercial orchards in the Fruit Ridge growing region of Michigan in which apple scab control failures were observed on ‘McIntosh’ apple following applications of kresoxim-methyl or trifloxystrobin. QoI resistance was assessed in 210 total isolates (a total of 17 orchards) using a spore germination assay and in 319 isolates using a polymerase chain reaction (PCR) assay to detect the G143A mutation located within the V. inaequalis cytochrome b gene (CYTB). The G143A mutation is known to confer high-level QoI resistance in plant-pathogenic fungi. QoI resistance was confirmed in 50 and 64% of the isolates tested with the spore germination and PCR assays, respectively, and there was a 97% concordance observed between the assays. In 2009, we sampled and examined an additional 1,201 V. inaequalis isolates from 64 orchards in Michigan and 86 isolates from four baseline sites in Ohio. All of these isolates were assayed for the G143A mutation and it was detected within 67 and 0% of the Michigan and Ohio isolates, respectively. Our results indicate the widespread occurrence of QoI resistance in Michigan commercial orchard populations of V. inaequalis. Loss of QoI fungicides further limits the arsenal of fungicides available to commercial apple growers for successful scab management.

scholarly journals Seasonal and Cross-Seasonal Timing of Fungicide Trunk Injections in Apple Trees to Optimize Management of Apple Scab

Plant Disease ◽  
2016 ◽  
Vol 100 (8) ◽  
pp. 1606-1616 ◽  
Author(s):  
Srđan G. Aćimović ◽  
Anthony H. VanWoerkom ◽  
Thomas Garavaglia ◽  
Christine Vandervoort ◽  
George W. Sundin ◽  
...  
Keyword(s):  
United States ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
The United States ◽  
Apple Trees ◽  
Seasonal Timing ◽  
Scab Control ◽  
Better Than ◽  
Spray Applications

To optimize the number and timing of trunk injections for season-long control of apple scab (Venturia inaequalis), we evaluated 1 to 2 and 4 seasonal and cross-seasonal injections of potassium phosphites and synthetic fungicides and quantified residues in leaves and fruit. Phosphites accumulated in the canopy at the highest concentrations, aligned well in time with scab suppression, and gave better leaf scab control of 41.8 to 73.5% than propiconazole (16.9 to 51.5%) or cyprodinil + difenoconazole (5.4 to 17.4%). More injections of phosphites controlled leaf scab better than fewer (23.7% versus 48.2%), and more fungicide injections resulted in 21.9 to 51.1% better leaf scab control than fewer. Leaf scab control with phosphites was only 3.2 to 13.9% better with 4 cross-seasonal compared with 4 seasonal injections, while 1 to 2 seasonal compared with 1 to 2 cross-seasonal injections improved scab control only for 4.2 to 22.1%. On shoots, injected phosphites provided comparable or for 4.4 to 10.5% and 22.3 to 41.4% better scab control than spray standards. On fruit, injected phosphites slightly improved control compared with sprayed phosphites or the sprayed fungicide standard (33.4 to 40.8%). Two seasonal injections of phosphites controlled shoot scab 5.7% better than 9 spray applications. Five sprays of cyprodinil + difenoconazole controlled scab better than their injections. Fruit residues of phosphites reached 2.8 ppm and declined in all treatments except in 2 seasonal injections and phosphite sprays. Cyprodinil and difenoconazole fruit residues reached 0.02 and 0.07 ppm and declined sharply toward the end of the season. These were far below the United States, Codex, and EU MRL-s of 1, 0.8, and 0.5 ppm for difenoconazole, and 1.7, 2, and 1 ppm for cyprodinil, respectively.

scholarly journals Toward an Integrated Use of Biological Control by Cladosporium cladosporioides H39 in Apple Scab (Venturia inaequalis) Management

Plant Disease ◽  
2015 ◽  
Vol 99 (4) ◽  
pp. 535-543 ◽  
Author(s):  
Jürgen Köhl ◽  
Christian Scheer ◽  
Imre J. Holb ◽  
Sylwester Masny ◽  
Wilma Molhoek
Keyword(s):  
Venturia Inaequalis ◽  
Apple Scab ◽  
Field Trials ◽  
Cladosporium Cladosporioides ◽  
Yield And Quality ◽  
Scab Control ◽  
Apple Production ◽  
First Time ◽  
Important Disease

Apple scab, caused by Venturia inaequalis, is the most important disease in apple production, reducing yield and quality of fruit. Control of apple scab in commercial orchards currently depends on multiple applications of fungicides. The potential of the antagonistic isolate Cladosporium cladosporioides H39, originating from a sporulating colony of V. inaequalis, to control apple scab development was tested in eight trials during 2 years in orchards in Eperjeske (Hungary), Dabrowice (Poland), and Bavendorf (Germany) planted with different cultivars. Treatments were conducted as calendar sprays or after infection periods. Additional trials in an orchard in Randwijk (The Netherlands) focused on the effect of timing of antagonist application before or after infection periods. The overall results of the field trials consistently showed—for the first time—that stand-alone applications of the antagonist C. cladosporioides H39 can reduce apple scab in leaves and fruit. This was demonstrated in an organic growing system as well as in conventional orchards by spray schedules applied during the primary or the summer season. In both systems, the same control levels could be reached as with common fungicide schedules. Efficacies reached 42 to 98% on leaf scab incidence and 41 to 94% on fruit scab. The antagonist was also effective if applied one or even several days (equivalent to approximately 300 to 2,000 degree h) after infection events in several field trials and a trial conducted in Randwijk with single-spray applications at different intervals before or after infection events. Better understanding of the biology of the antagonist will help to further exploit its use in apple scab control.

scholarly journals The Effect of Delayed-Dormant Chemical Treatments on Demethylation Inhibitor (DMI) Sensitivity in a DMI-resistant Population of Venturia inaequalis

Plant Disease ◽  
2015 ◽  
Vol 99 (12) ◽  
pp. 1751-1756 ◽  
Author(s):  
Zachary A. Frederick ◽  
Sara M. Villani ◽  
Kerik D. Cox
Keyword(s):  
New York ◽  
Treatment Program ◽  
Management Practices ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Fungicide Treatment ◽  
Chemical Treatments ◽  
Dmi Fungicides ◽  
The Impact ◽  
Demethylation Inhibitor

Demethylation inhibitor (DMI) fungicides are an effective means to manage apple scab caused by Venturia inaequalis. Unfortunately, practical resistance to DMI fungicide chemistries is prevalent in populations in New York and the New England states. Management practices that delay the development of DMI resistance in V. inaequalis populations are highly desired by regional apple producers. Trials were conducted in a New York apple orchard during the 2011 and 2012 growing seasons to determine the impact of delayed-dormant (after bud break, but prior to green tissue) chemical treatments on the DMI sensitivity of a V. inaequalis population with stable resistance to DMI fungicides. Delayed-dormant treatment programs consisted of either an application of a copper fungicide, a manganese sanitation product, a DMI fungicide (myclobutanil), or no fungicide. Sensitivity to the DMI fungicide myclobutanil was evaluated for a minimum of 25 V. inaequalis single lesion conidial isolates from each of four replicated treatment blocks. In both years, mean percent relative growth on myclobutanil amended media for V. inaequalis isolates from the copper treatment program were significantly (P < 0.05) lower than isolates from blocks did not receive a delayed dormant fungicide treatment. The effect of the manganese treatment was inconsistent between years. V. inaequalis isolates collected from the myclobutanil treatment program were not significantly (P > 0.05) different in myclobutanil sensitivity from isolates collected from the blocks that did not receive a delayed dormant fungicide treatment. Overall, the results suggest that delayed dormant treatments of copper may favorably impact the myclobutanil sensitivity for a population of V. inaequalis with resistance to DMI fungicides, and should be considered as a standard management practice in apple production.

scholarly journals Investigation of Fungicidal Properties of the Tree Growth Regulator Paclobutrazol to Control Apple Scab

2006 ◽  
Vol 32 (2) ◽  
pp. 67-73
Author(s):  
Ryan Blaedow ◽  
William Chaney ◽  
Paul Pecknold ◽  
Harvey Holt
Keyword(s):  
Growth Regulator ◽  
Foliar Application ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Systemic Fungicide ◽  
Growth Reduction ◽  
Mature Trees ◽  
The Third ◽  
Snow Drift ◽  
Scab Control

Paclobutrazol (PBZ) as a systemic fungicide for control of apple scab (Venturia inaequalis) was investigated in mature (cv. Hopa and Snow Drift) and young sapling (cv. Indian Magic) crabapples (Malus spp.). Treatments consisted of a control and PBZ applied to mature trees at one or two times the recommended rate in April 2002 using the basal drench method. Saplings received either foliar or soil drench applications of PBZ, or foliar applications of propiconazole. Disease assessments of mature trees showed that apple scab symptoms in treated trees were as severe as in untreated ones in the year of treatment but were reduced slightly the year after treatment in ‘Hopa’ and the third year after treatment in ‘Snow Drift.’ Growth reduction occurred in all treated trees, suggesting that the PBZ levels needed for growth reduction were not sufficient to control apple scab in the year of treatment. In contrast, a one-time foliar application of PBZ reduced apple scab incidence to levels found in ‘Indian Magic’ saplings treated every 2 weeks with propiconazole, a fungicide and application method commonly recommended for apple scab control. Delayed uptake and insufficient transport of PBZ to the foliage of mature trees after root drench treatments may account for the lack of apple scab control in the years after treatment, even though growth suppression occurred.

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