Aristotelian University, Faculty of Agriculture, Plant Pathology Laboratory, P.O.B. 269, Thessaloniki, GR 540 06, Greece
Field experiments were conducted during the 1989 to 1993 growing seasons in order to determine the effect of natural infections of Alternaria alternata on yield of sunflower (Helianthus annuus). Number of seeds produced per head and seed weight were reduced by 16 to 65% and 15 to 79%, respectively. Number and weight of seeds produced per head were correlated negatively with disease intensity before anthesis. The fungus overwinters in sunflower leaf residues and may present a yearly problem for sunflower production in some areas.