Fungicide Sensitivity of Colletotrichum Species Causing Bitter Rot of Apple in the Mid-Atlantic U.S.A.

Apple growers in the Mid-Atlantic region of the U.S.A. have reported increased losses to bitter rot of apple. We tested the hypothesis that this increase is because the Colletotrichum population has developed resistance to commonly used single-mode-of-action (single-MoA) fungicides. We screened 220 Colletotrichum isolates obtained from 38 apple orchards in the Mid-Atlantic region for resistance to 11 fungicides in Fungicide Resistance Action Committee (FRAC) groups 1, 7, 9, 11, 12, and 29. Eleven (5%) of these isolates were resistant to FRAC group 1 with confirmed ß-tubulin E198A mutations, and two (<1%) were also resistant to FRAC group 11 with confirmed cytochrome-b G143A mutations. Such low frequencies of resistant isolates indicate that fungicide resistance is unlikely to be the cause of any regional increase in bitter rot. A subsample of isolates was subsequently tested in vitro for sensitivity to every single-MoA fungicide registered for apple in the Mid-Atlantic U.S.A. (22 fungicides; FRAC groups 1, 3, 7, 9, 11, 12, and 29), and 13 fungicides were tested in field trials. These fungicides varied widely in efficacy both within and between FRAC groups. Comparisons of results from our in vitro tests with results from our field trials and other field trials conducted across the eastern U.S.A. suggested that EC25 values (concentrations that reduce growth by 25%) are better predictors of fungicide efficacy in normal field conditions than EC50 values. We present these results as a guideline for choosing single-MoA fungicides for bitter rot control in the Mid-Atlantic U.S.A.

Advantageous properties of a new fungicide, isofetamid.

The fungicidal properties of a new fungicide, isofetamid, were examined to assess its antifungal spectrum, mode of action, and effects on the infection process of Botrytis cinerea. Additionally, we investigated its fungicidal activity against isolates of B. cinerea resistant to existing fungicides. In mycelial growth inhibition tests, isofetamid exhibited excellent fungicidal activity against ascomycetes but showed no activity against basidiomycetes and oomycetes. Respiratory enzyme assay using mitochondria revealed that isofetamid inhibited succinate dehydrogenase activity prepared from B. cinerea and other ascomycetes fungi used in the study. On the other hand, the activity of mitochondria prepared from Pythium, potato and rat were not inhibited. Isofetamid inhibited also many stages of the infection processes in B. cinerea. Furthermore, it exhibited high fungicidal activity against B. cinerea isolates that were resistant to existing fungicides.

Modification of the existing maximum residue levels for isofetamid in certain salad plants.

In accordance with Article 6 of Regulation (EC) No 396/2005, the applicant ISK Biosciences Europe N.V. submitted a request to the competent national authority in Belgium to modify the existing maximum residue levels (MRLs) for the active substance isofetamid in certain salad plants. The data submitted in support of the request were found to be sufficient to derive MRL proposals for lamb's lettuces/corn salads, escaroles/broad leaved endives, cresses and other sprouts and shoots, land cresses, Roman rocket/rucola, red mustards, baby leaf crops (including brassica species) and other lettuces and salad plants. An adequate analytical method for enforcement is available to enforce the residues of isofetamid on the commodities under consideration at the validated limit of quantification (LOQ) of 0.01 mg/kg. Based on the risk assessment results, EFSA concluded that the short-term and long-term intake of residues resulting from the uses of isofetamid according to the reported agricultural practices is unlikely to present a risk to consumer health.

Modification of the existing maximum residue levels for isofetamid in raspberries, blackberries and dewberries.

In accordance with Article 6 of Regulation (EC) No 396/2005, the applicant ISK Biosciences Europe N.V. submitted a request to the competent national authority in Belgium to modify the existing maximum residue levels (MRLs) for the active substance isofetamid in raspberries, blackberries and dewberries. The data submitted in support of the request were found to be sufficient to derive MRL proposals for blackberries, dewberries and raspberries. Adequate analytical methods for enforcement are available to control the residues of isofetamid in the commodities under consideration at the validated limit of quantification (LOQ) of 0.01 mg/kg. Based on the risk assessment results, EFSA concluded that the short-term and long-term intake of residues resulting from the use of isofetamid according to the reported agricultural practices is unlikely to present a risk to consumer health.

Residue analysis of fungicides fenpicoxamid, isofetamid, and mandestrobin in cereals using zirconium oxide disposable pipette extraction clean-up and ultrahigh-performance liquid chromatography-tandem mass spectrometry.

In the present study, a fast multiresidue method determining three novel fungicides fenpicoxamid, isofetamid, and mandestrobin in cereals was developed and validated for the first time using ultrahigh-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Samples were extracted by QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) methodology, and cleaned up using the disposable pipette extraction (DPX) tips containing primary secondary amine (PSA) and silica gel modified with zirconium oxide (Z-Sep) in less than 1 min. Linearity (r > 0.99) of three fungicides in the calibration range of 0.001-0.1 µg mL-1 was satisfactory. Mean recoveries (n = 15) from all matrices were between 84.8% and 100.3% as the corresponding intra-day and inter-day relative standard deviations (RSDs) were less than 10.6%. Limits of quantitation (LOQs) of all analytes in different matrices were defined at 0.01 mg kg-1. The results indicate this method can serve as a sensitive and rapid approach to monitoring contents of fenpicoxamid, isofetamid, and mandestrobin in cereals.

Modification of the existing maximum residue levels for isofetamid in tomatoes, peppers, aubergines, okra and cucurbits with edible peel.

In accordance with Article 6 of Regulation (EC) No 396/2005, the applicant ISK Biosciences Europe N.V. submitted a request to the competent national authority in Belgium, to modify the existing maximum residue levels (MRL) for the active substance isofetamid in tomatoes, sweet peppers/bell peppers, aubergines/eggplants, okra/lady's fingers and the whole subgroup of cucurbits with edible peel. The data submitted in support of the request were found to be sufficient to derive MRL proposals for the commodities under evaluation. Adequate analytical methods for enforcement are available to control the residues of isofetamid in the commodities under consideration at the validated limit of quantification (LOQ) of 0.01 mg/kg. Based on the risk assessment results, EFSA concluded that the short-term and long-term intake of residues resulting from the use of isofetamid according to the reported agricultural practices is unlikely to present a risk to consumer health. The reliable end points appropriate for use in regulatory risk assessment are presented.

Non-target site SDHI resistance is present as standing genetic variation in field populations of Zymoseptoria tritici.

BACKGROUND: A new generation of more active succinate dehydrogenase (Sdh) inhibitors (SDHIs) is currently widely used to control Septoria leaf blotch in northwest Europe. Detailed studies were conducted on Zymoseptoria tritici field isolates with reduced sensitivity to fluopyram and isofetamid; SDHIs which have only just or not been introduced for cereal disease control, respectively. RESULTS: Strong cross-resistance between fluopyram and isofetamid, but not with other SDHIs, was confirmed through sensitivity tests using laboratory mutants and field isolates with and without Sdh mutations. The sensitivity profiles of most field isolates resistant to fluopyram and isofetamid were very similar to a lab mutant carrying SdhC-A84V, but no alterations were found in SdhB, C and D. Inhibition of mitochondrial Sdh enzyme activity and control efficacy in planta for those isolates was severely impaired by fluopyram and isofetamid, but not by bixafen. Isolates with similar phenotypes were not only detected in northwest Europe but also in New Zealand before the widely use of SDHIs. CONCLUSION: This is the first report of SDHI-specific non-target site resistance in Z. tritici. Monitoring studies show that this resistance mechanism is present and can be selected from standing genetic variation in field populations. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.