Evaluation of sensitivity of apple scab pathogen to difenoconazole using the discriminatory dose technique

The most serious disease of the apple tree in all areas its growth is scab. In integrated protection system, main method chemical. However, use chemical fungicides characterized by risk developing resistance to them pathogen. sensitivity 118 monospore isolates Venturia inaequalis was studied from three orchards Jeromine, Reinette Simirenko and Gala cultivars, differing frequency application difenoconazole. Sensitivity determined using discriminatory dose technique (0.01 mg/l active substance) terms RG, relative mycelium. RG expressed as degree change mycelium a nutrient medium with fungicide control variant percent. All pathogen populations differed significantly mean values. Populations treated times per season difenoconazole had higher values compared two times. From orchard, for some isolates, stimulating effect on their observed, that is, hormesis manifested. proportion above cutoff value, which 84 100 % orchards, may indicate are resistant, these there be decrease effectiveness against allowed us objectively promptly assess V. varying intensity