Achene blemish syndrome: a new disease of sunflower in Israel.
A new disease affecting sunflower achenes in Israel is reported. Infection produces small, scattered lesions on the surface of the shell. Lesions were brown, black or grey and some were surrounded by dark halos, ranging in size from 0.5 to 2 mm. These lesions were round, oval, elongate or irregular in shape. Several fungi were isolated from infected achenes and Koch's postulates were completed for Alternaria alternata, Cladosporium sp. and Ulocladium atrum. Artificial inoculation trials revealed that A. alternata induced a significantly higher disease incidence than the other 2 fungi and that inoculation with a mixture containing spores of all 3 fungi resulted in a higher disease incidence than that obtained by inoculation with each pathogen alone. Achenes were susceptible to infection only at the time of their development, but symptoms were only visible just before physiological maturity. A field trial demonstrated that Frankliniella occidentalis is associated with infection of the achenes. The effects of 9 fungicides (hexaconazole, maneb, iprodione, fenbuconazole, promoconazole, cyproconazole, tebuconazole, difenoconazole and oxine-copper) on disease severity were examined in 2 field trials in 1992. It is concluded that, although some fungicides significantly reduced disease severity, their effect was relatively minor and in general they were not highly effective.