Search Results (4)

Venturia inaequalis, the cause of apple scab, readily develops resistance to fungicides with specific modes of action. Knowledge of the spatial and temporal pattern of resistance development is therefore relevant to fruit producers and their consultants. In the Lower Elbe region of Northern Germany, a two-year survey based on a conidial germination test was conducted, examining fungicide resistance in 35 orchards under Integrated Pest Management (IPM), 16 orchards of susceptible cultivars as well as a further 12 orchards of scab-resistant (Vf) cultivars under organic management, and 34 abandoned or unmanaged sites. No evidence of resistance to SDHI compounds (fluopyram, fluxapyroxad) was found after >5 yr of their regular use. Resistance to anilinopyrimidines (cyprodinil, pyrimethanil) had disappeared 15 yr after its widespread occurrence. Isolates from a few IPM orchards showed a reduced sensitivity to dodine. Double resistance to the MBC compound thiophanate-methyl and the QoI trifloxystrobin was rare in V. inaequalis strains that had achieved breakage of Vf-resistance, but very common (>50%) on scab-susceptible cultivars in IPM, organic and abandoned orchards in the ‘Altes Land’ core area of the Lower Elbe region, and in IPM orchards in the periphery. We conclude that resistance to QoI and MBC fungicides is persistent even decades after their last use, and that the core area harbours a uniform population adapted to intensive crop protection, whereas isolated orchards in the periphery are colonised by discrete populations of V. inaequalis. Full article

Fluopyram and trifloxystrobin are widely used for controlling various plant diseases in cucumbers and cowpeas. However, data on residue behaviors in plant cultivation and food processing are currently lacking. Our results showed that cowpeas had higher fluopyram and trifloxystrobin residues (16.48–247.65 μg/kg) than cucumbers (877.37–3576.15 μg/kg). Moreover, fluopyram and trifloxystrobin dissipated faster in cucumbers (half-life range, 2.60–10.66 d) than in cowpeas (10.83–22.36 d). Fluopyram and trifloxystrobin were the main compounds found in field samples, and their metabolites, fluopyram benzamide and trifloxystrobin acid, fluctuated at low residue levels (≤76.17 μg/kg). Repeated spraying resulted in the accumulation of fluopyram, trifloxystrobin, fluopyram benzamide and trifloxystrobin acid in cucumbers and cowpeas. Peeling, washing, stir-frying, boiling and pickling were able to partially or substantially remove fluopyram and trifloxystrobin residues from raw cucumbers and cowpeas (processing factor range, 0.12–0.97); on the contrary, trifloxystrobin acid residues appeared to be concentrated in pickled cucumbers and cowpeas (processing factor range, 1.35–5.41). Chronic and acute risk assessments suggest that the levels of fluopyram and trifloxystrobin in cucumbers and cowpeas were within a safe range based on the field residue data of the present study. The potential hazards of fluopyram and trifloxystrobin should be continuously assessed for their high residue concentrations and potential accumulation effects. Full article

Fusarium basal rot disease (FBR) is considered a serious threat to commercial onion production in Israel and worldwide. Today, coping means applied in Israel against the disease have limited efficiency and include a four-year crop cycle and disinfecting the soil with metam sodium. At the same time, agricultural tools (harrows, plows, etc.), contaminated equipment and workers facilitate spread of the disease to new growth areas, and the field disease incidence in Israel now reaches 8% of yields in heavily infected areas. Infected onions do not always show disease symptoms and the problem worsens if they arrive at storage facilities, especially since this pathogen genus produces known toxins. The current study aims at examining the potential of chemical control to reduce the damage caused by this disease. To this end, nine commercial fungicides were scanned in plate sensitivity assay against the main pathogens involved, Fusarium oxysporum f. sp. cepae and Fusarium acutatum. Several fungicides were found to be highly effective against the two pathogens, especially the mixtures Azoxystrobin + Difenoconazole, Fluopyram + Trifloxystrobin, or the Fluazinam compounds. Three selected preparations previously tested in seedlings were evaluated here in a full growing season. Prochloraz successfully protected the Orlando variety (white onion, Riverside cv.) and the Noam variety (red onion) at all growth stages against F. oxysporum f. sp. cepae. At the same time, this treatment was ineffective against F. acutatum in Noam cv. Another anti-fungal preparation, Fludioxonil + Sedaxen mixture, showed a wider range of effectiveness at the season’s end against the two Fusarium species tested in both onion cultivars. These results are an important step towards developing FBR control in commercial onion fields. Follow-up work is needed to optimize the pesticides’ concentrations and their application methods and to test them on a field scale. Interestingly, these pathogens were more aggressive towards the cultivar from which they were isolated: F. oxysporum f. sp. cepae to the red onion Noam cv. and F. acutatum to the white Orlando cv. Infecting the plants with both pathogens reduced disease symptoms in the white Orlando cv, suggesting antagonistic interactions in this onion genotype. Full article

Red leaf blotch (RLB) of almond, caused by Polystigma amygdalinum, is an important foliar disease of this nut tree in the Mediterranean basin and especially in Spain. In recent years, the control of this disease has become a key factor in the management of Spanish almond orchards. The management of RLB is not easy due to intrinsic factors of the disease (e.g., long infection and latency periods) and the low number of registered fungicides in this country. From 2015 to 2019, different field trials were conducted in the Lleida region, NE Spain, to evaluate the efficacy of several fungicide products and of application strategies to control this disease. Systemic fungicides, which included fluopyram, trifloxystrobin, and mixtures of fluopyram + trifloxystrobin and pyraclostrobin + boscalid, performed better than contact and penetrant products and showed up to 90% control against RLB. However, the efficacy of the tested fungicides varied depending on the year. In terms of application strategies, when fungicide applications were conducted following specific meteorological conditions (after 15 days from >15 mm rainfalls with ≈10–15 °C as the minimum average temperature), their efficacy was comparable to that of calendar-based treatments (every 14, 21, or 31 days from petal fall) but with fewer applications (depending on the year, 2–4 applications as compared with 5–9 for calendar treatments). Full article