scholarly journals Managing Resistance of Venturia inaequalis to the Strobilurin Fungicides

2004 ◽  
Vol 5 (1) ◽  
pp. 3 ◽  
Author(s):  
William W. Turechek ◽  
Wolfram Köller
Keyword(s):  
Fungicide Resistance ◽  
Large Scale ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Resistance Management ◽  
Management Program ◽  
Crop Losses ◽  
The Past ◽  
Strobilurin Fungicides ◽  
Low Rate

Over the past thirty years, fungicide resistance has been cited as the cause of large-scale crop losses due to apple scab in a number of commercial orchards in the Northeast. The strobilurins represent the most recent class of fungicides for which the threat of resistance exists. In this article we examine the use of strobilurin fungicides at their highest and lowest labeled rates and as a mixture of the lowest labeled rate with a protectant fungicide in commercial spray programs for efficacy against apple scab as well as their utility in a resistance management program. Our results suggest that anti-resistance properties of high strobilurin rates are superior to low rates and low rate mixtures with a protectant fungicide. Accepted for publication 26 August 2004. Published 8 September 2004.

scholarly journals Evidence for the Predisposition of Fungicide-Resistant Isolates of Venturia inaequalis to a Preferential Selection for Resistance to Other Fungicides

2001 ◽  
Vol 91 (8) ◽  
pp. 776-781 ◽  
Author(s):  
Wolfram Köller ◽  
W. F. Wilcox
Keyword(s):  
Fungicide Resistance ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
The United States ◽  
Cross Resistance ◽  
Resistance Development ◽  
Flexible Response ◽  
Sterol Demethylation Inhibitors ◽  
Selection For ◽  
Selection Of

In the United States, populations of the apple scab pathogen Venturia inaequalis have progressed through three consecutive rounds of fungicide resistance development, first to dodine, then to the benzimidazoles, and most recently to the sterol demethylation inhibitors (DMIs). Analysis of extensive monitoring data have to date provided no indication of detectable cross-resistance or partial cross-resistance of V. inaequalis populations to the three unrelated classes of fungicides prior to the selection of resistant subpopulations. However, in this study, resistance to both benomyl and DMIs developed to significantly higher frequencies within the previously established dodine-resistant population than in the population sensitive to dodine. Accelerated selection of phenotypes double resistant to dodine and the DMI fenarimol was apparent over the course of distinct seasons of apple scab management with either dodine or fenarimol. The data provide evidence for an accelerated speed of resistance development among phenotypes of V. inaequalis already resistant to an unrelated fungicide. This finding represents a departure from the previous model, which assumed entirely independent rounds of resistance developments. The data indicate that phenotypes of V. inaequalis might not only be selected for the trait of fungicide resistance but also for traits allowing a more flexible response to changes in the environment where they compete.

Resistance to Myclobutanil in Populations of Venturia inaequalis in Winchester, Virginia

2007 ◽  
Vol 8 (1) ◽  
pp. 3 ◽  
Author(s):  
Sasha C. Marine ◽  
David G. Schmale ◽  
Keith S. Yoder
Keyword(s):  
Fungicide Resistance ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Apple Orchards ◽  
The Mean ◽  
Moderately Resistant

Sterol-inhibiting (SI) fungicides are widely used to manage apple scab, caused by Venturia inaequalis. However, recent observations indicate that populations of V. inaequalis in orchards in Virginia have developed resistance to myclobutanil and other SI fungicides. Little is known about the frequency and distribution of fungicide resistance in apple scab populations in Virginia. Isolates of V. inaequalis were collected from three different apple orchards in Winchester, VA in 2006. Orchards were treated with myclobutanil on 12 April, 19 April, 1 May, 30 May, and 7 July. The sensitivity of 87 single-spored isolates of V. inaequalis to myclobutanil was determined by monitoring their growth on agar dishes amended with 0, 0.1, 0.5, or 1.0 μg/ml myclobutanil. A relative continuum of fungicide resistance was observed: 16 isolates were resistant, 40 isolates were moderately resistant, and 31 isolates were sensitive to myclobutanil. After 28 days, the mean growth of isolates collected from trees treated with myclobutanil was significantly greater than that of isolates collected from non-treated trees at all concentrations of myclobutanil tested in vitro. High levels of fungicide resistance found in populations of V. inaequalis suggest that replacement programs may need to be developed to manage apple scab in Virginia. Accepted for publication 4 September 2007. Published 13 November 2007.

scholarly journals Identification of Resistance to Multiple Fungicides in Field Populations of Venturia inaequalis

Plant Disease ◽  
2011 ◽  
Vol 95 (8) ◽  
pp. 921-926 ◽  
Author(s):  
Kimberly S. Chapman ◽  
George W. Sundin ◽  
Janna L. Beckerman
Keyword(s):  
Fungicide Resistance ◽  
Mycelial Growth ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Field Resistance ◽  
Single Spore ◽  
Mycelium Growth ◽  
Thiophanate Methyl ◽  
Development Of Resistance

Venturia inaequalis, the causal agent of apple scab, is controlled primarily by fungicides. Long-term, extensive fungicide use has led to the development of resistance to multiple fungicides. To assess fungicide resistance, isolates of V. inaequalis were collected from Indiana and Michigan orchards. Single-spore derived isolates were evaluated by mycelium growth assays with previously determined discriminatory doses on media containing dodine, kresoxim-methyl, myclobutanil, or thiophanate-methyl. Of 195 isolates tested, 5.2, 0.7, 57.0, and 92.6% of isolates were found to be resistant to dodine, kresoxim-methyl, myclobutanil, and thiophanate-methyl, respectively. This is the first report of kresoxim-methyl field resistance in these states. Isolates resistant or shifted to a single fungicide were often found to have multiple fungicide resistance. Of all isolates tested, 38% were identified as resistant or shifted to two fungicides, and 12% were resistant or shifted to all four fungicides tested. No fitness penalty was found for isolates resistant to multiple fungicides based on a statistical analysis of mycelial growth and conidial production.

scholarly journals Efficacy loss of strobilurins used in protection against apple scab in Czech orchards

2013 ◽  
Vol 40 (No. 2) ◽  
pp. 45-51 ◽  
Author(s):  
P. Sedlák ◽  
R. Vávra ◽  
P. Vejl ◽  
S. Boček ◽  
J. Kloutvorová
Keyword(s):  
High Frequency ◽  
Venturia Inaequalis ◽  
Single Point ◽  
Apple Scab ◽  
Point Mutations ◽  
Cytb Gene ◽  
The Past ◽  
Resistant Population ◽  
Single Point Mutations ◽  
Selective Environment

The apple scab caused by Venturia inaequalis is important apple disease in temperate zone. Economical losses caused by the pathogen are effectively reduced by intensive chemical protection and breeding. Occurrences of pathogen resistence to strobilurin fungicides were noted in some Czech orchards in the past. In 2007–2011, collection of 136 isolates V. inaequalis was tested with the aim to detect presence of single-point mutations of cytochrom b (cytb) gene causing efficacy loss of strobilurins. Consequently occurrence of beta-tubulin (beta-tub) gene mutation causing resistance to benomyl was studied with the aim to obtain comparative data about frequency of mutation in non-selective environment. Therefore simple and highly repeatable PCR based mutation detecting methods were optimised. Analysis brought knowledge about high similarity of cytb and beta-tub genes mutations occurrence. Whilst the frequency of the G143A substitution in cytb gene was 65% the E198A substitution of beta-tub gene occurred in 54% within pathogen population. This high frequency of resistant population necessitates revision of the way of strobilurins use in apple scab management.    

Resistance to Dodine in Populations of Venturia inaequalis in Quebec, Canada

2010 ◽  
Vol 11 (1) ◽  
pp. 17 ◽  
Author(s):  
Odile Carisse ◽  
Tristan Jobin
Keyword(s):  
Management Strategy ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Resistance Management ◽  
Cross Resistance ◽  
Wild Type ◽  
The Usa ◽  
Control Failure ◽  
Type Population ◽  
Two Populations

Dodine was introduced in the USA and Canada in the early 1960s for the control of apple scab. Following control failure, growers stopped using dodine in the mid-1970s. Despite the curtailment of dodine use more than 30 years ago, persistent resistance to the fungicide was suspected in V. inaequalis populations. The dodine sensitivity was determined for two populations that were not exposed to dodine for at least 30 years – a wild type population (25 monoconidial isolates) and a population constructed with isolates collected in orchards managed for apple scab (156 isolates). The sensitivity to dodine was determined by monitoring growth of these isolates on agar Petri dishes amended with 0, 0.01, 0.1, 1.0, or 10.0 μg/ml of dodine. Sensitivity to fungicide was evaluated based on ED50 values. Both populations showed a lognormal distribution of ED50 values. The ED50 means were 0.525 μg/ml and 1.735 μg/ml for the wild type and managed orchards populations, respectively. In managed orchard, 31.4% of the isolates were resistant to dodine (ED50 > 1.0 μg/ml). Cross-resistance with myclobutanil and with kresoxim-methyl was tested and found not to be significant. The results of this study suggest that resistance to dodine is still present in the populations of V. inaequalis from Quebec and that reintroduction of dodine should only be done along with an appropriate resistance management strategy. Accepted for publication 27 April 2010. Published 14 June 2010.

scholarly journals Effect of eradicative activity of strobilurin fungicides and difenconazole on mycelium and sporulation of Venturia inaequalis

2013 ◽  
Vol 55 (1) ◽  
pp. 49-58
Author(s):  
Agata Broniarek-Niemiec ◽  
Anna Bielenin ◽  
Barbara Dyki
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Field Condition ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Field Conditions ◽  
Strobilurin Fungicides ◽  
Strobilurin Fungicide ◽  
Scanning Electron

The eradicative effect of two strobilurin fungicides (kresoxim-methyl and trifloxystrobin) and difenoconazole on activity of apple scab spots was studied in greenhouse and field conditions. The reaction of mycelium and sporulation of <i>Venturia inaequalis</i> after fungicides applications were observed in light and scanning electron microscope. Mixture of strobilurin fungicide and difenoconazole applied twice, in 5 days interval, gave the best eradicative effect. The inhibition of sporulation was long lasting and it was observed even 3 and 5 weeks after treatments. The conidiophores, conidia and mycelium were damaged. Also difenoconazole showed good eradicative activity, in field condition up to 5 weeks after application. Trifloxystrobin significantly reduced the number of active scab lesions and the effect was visible even 3 weeks after treatment. Kresoxim-methyl in both tested doses (0,2 and 0,3 kg/ha) was slightly less effective.

scholarly journals Evaluation of Tactics for Managing Resistance of Venturia inaequalis to Sterol Demethylation Inhibitors

Plant Disease ◽  
1999 ◽  
Vol 83 (9) ◽  
pp. 857-863 ◽  
Author(s):  
Wolfram Köller ◽  
W. F. Wilcox
Keyword(s):  
Venturia Inaequalis ◽  
Apple Scab ◽  
Run Off ◽  
Equivalent Control ◽  
Sterol Demethylation Inhibitors ◽  
The Individual ◽  
And Control ◽  
The Impact ◽  
Low Rate ◽  
Selection Of

The impact on the selection and control of subpopulations of V. inaequalis resistant to the sterol demethylation inhibitor (DMI) fenarimol or to dodine were evaluated with respect to several tactics of apple scab control. Experiments were conducted in an experimental orchard with elevated levels of DMI and dodine resistance over a period of three consecutive seasons. The DMI-resistant subpopulation was poorly (14%) controlled at a fenarimol rate of 15 mg/liter (sprayed to run-off), whereas control was significantly improved (54%) at twice that rate. Mancozeb mixed with the low rate of fenarimol also improved the control of DMI-resistant isolates, but the improvement was due to the indiscriminate control of both the DMI-sensitive and -resistant populations provided by mancozeb. The selection of fenarimol-resistant isolates resulting from poor control of the resistant subpopulation by the low rate of fenarimol was equivalent whether fenarimol was applied singly or in mixture with mancozeb. Consequently, the use of high DMI rates in mixture with a protective fungicide is expected to delay the build-up of resistant subpopulations by limiting their increase through two separate principles of control. For dodine in mixture with fenarimol, it was found that each mixing partner applied alone selected both fe-narimol- and dodine-resistant isolates. This selection pattern was partly explained by the possibility that one of the multiple genes underlying fenarimol and dodine resistance confers resistance to both fungicides, in addition to the selection of double-resistant isolates. Regardless, a mixture of fenarimol with dodine each employed at a low rate controlled both the fenarimol-and the dodine-resistant subpopulation at least as effectively as the individual components at twice their mixture rate, and an accelerated selection of double-resistant isolates was not detected. In commercial orchard trials, mixtures of DMIs with either a protective fungicide or with dodine provided equivalent control even when levels of DMI resistance, dodine resistance, or both were moderately elevated. With the exception of orchards with high levels of DMI or dodine resistance, dodine might be an alternative to protective fungicides as a mixing partner with DMIs.

scholarly journals Application of fungicides during leaf fall to control apple scab (Venturia inaequalis) in the following season

2008 ◽  
Vol 61 ◽  
pp. 59-64 ◽  
Author(s):  
R.M. Beresford ◽  
P.N. Wood ◽  
P.W. Shaw ◽  
T.J. Taylor
Keyword(s):  
Fungicide Resistance ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Fruit Production ◽  
Leaf Fall ◽  
Apple Orchards ◽  
Resistance Risk ◽  
Chemical Residues ◽  
Integrated Fruit Production

Leaf fall applications of fungicides to reduce scab in apple orchards were investigated to reduce reliance on summer fungicides that can cause trace chemical residues on harvested fruit Two applications of fungicides including captan tolyfluanid myclobutanil and urea were made at 1020 and 5060 leaf fall in four orchard trials in Nelson and Hawkes Bay using the cultivars Royal Gala Braeburn Fuji and Sciros/Pacific Rosetrade; Trial orchards received standard spring and summer fungicide programmes that complied with Integrated Fruit Production and were monitored for leaf and fruit scab in December and at harvest Significant reductions in leaf or fruit scab occurred in three out of five comparisons involving different sites years and cultivars suggesting that autumn applications can reduce scab in the following season Captan and tolyfluanid appeared most useful for autumn application Myclobutanil should not be used because of the fungicide resistance risk Results with urea were variable

scholarly journals The Effects of Succinate Dehydrogenase Inhibitor Fungicide Dose and Mixture on Development of Resistance in Venturia inaequalis

2020 ◽  
Vol 86 (17) ◽  
Author(s):  
Katrin M. Ayer ◽  
Mei-Wah Choi ◽  
Stephanie T. Smart ◽  
April E. Moffett ◽  
Kerik D. Cox
Keyword(s):  
Disease Management ◽  
Succinate Dehydrogenase ◽  
Fungicide Resistance ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Perennial Crops ◽  
Fungicide Application ◽  
Development Of Resistance ◽  
Succinate Dehydrogenase Inhibitor ◽  
Different Doses

ABSTRACT Understanding how fungicide application practices affect selection for fungicide resistance is imperative for continued sustainable agriculture. Here, we examined the effect of field applications of the succinate dehydrogenase inhibitor (SDHI) fluxapyroxad at different doses and mixtures on the SDHI sensitivity of Venturia inaequalis, the apple scab pathogen. Fungicide applications were part of selection programs involving different doses (high or low) and mixtures (with a second single-site fungicide or a multisite fungicide). These programs were tested in two apple orchards over 4 years to determine potential cumulative selection effects on resistance. Each year after program applications, apple scab lesions were collected, and relative growth assays were conducted to understand shifts in fluxapyroxad sensitivity. After 4 years, there was a trend toward a reduction in sensitivity to fluxapyroxad for most selection programs in comparison to that in the non-selective-pressure control. In most years, the selection program plots treated with low-dose fluxapyroxad applications resulted in a larger number of isolates with reduced sensitivity, supporting the use of higher doses for disease management. Few significant differences (P < 0.05) in fungicide sensitivity were observed between isolates collected from plots where fungicide mixtures were applied compared to that in untreated plots, supporting the use of multiple modes of action in field applications. In all, appropriate doses and mixtures may contribute to increased longevity of SDHI fungicides used on perennial crops like apples. IMPORTANCE Of much debate is the effect of fungicide application dose on resistance development, as fungicide resistance is a critical barrier to effective disease management in agricultural systems. Our field study in apples investigated the effect of fungicide application dose and mixture on the selection of succinate dehydrogenase inhibitor resistance in Venturia inaequalis, a fungal pathogen that causes the economically important disease apple scab. Understanding how to best delay the development of resistance can result in increased efficacy, fewer applications, and sustainable fungicide use. Results from this study may have relevance to other perennial crops that require multiple fungicide applications and that are impacted by the development of resistance.

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