POSTINFECTION FUNGICIDAL INHIBITION OF APPLE SCAB (VENTURIA-INAEQUALIS) SPORULATION

An experiment was conducted during 1986 and 1987 to study the pm-symptom (2 days before symptom appearance) activity of fungicides in the control of apple scab [Venturia inaequalis (Cooke) Winter] under controlled glass-house conditions. Single application of bitertanol (0.075%), prochloraz (0.03%), triforine (0.075%), etaconazole (0.03%), myclobutanil (0.075%), penconazole + captan (0.15%), fenarimol (0.03%), carbendazim (0.05%), thiophanate-methyl (0.05%) and guazatine (0.15%) changed the appearance of typical olive scab lesions to reddish-brown flecks. The reddish-brown flecks showed reduced sporulation and poor conidial germination. Carbendazim (0.05%), dodine (0.075%) and myclobutanil (0.075%) were more effective on conidial production, whereas bitertanol (0.075%) and myclobutanil (0.075%) inhibited conidial germination significantly. However, the post-symptom activity of hexaconazole (0.04%). prochloraz (0.03%), dodine (0.075%), bitertanol (0.075%) and thiophanate-methyl (0.05%) reduced the conidial production and germination significantly when applied on sporulating lesions under controlled and orchard conditions.