ACHENE BLEMISH SYNDROME - A NEW DISEASE OF SUNFLOWER IN ISRAEL

A new disease has affected sunflowre (Helianthus annuus) achenes in Is rael. Infection produces small, scattered lesions on the surface of th e shell. Lesions are brown, black, or gray and some are surrounded by dark halos; they range in size from 0.5 to 2 mm and may be round, oval , elongate, or irregular. Infected crops are viewed by the industry as being of lower quality and therefore fetch a lower market price. Seve ral fungi were isolated from infected achenes. The four steps of 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 o ther two fungi and that inoculation with a mixture containing spores o f all three fungi resulted in a higher disease incidence than that obt ained by inoculation with each pathogen alone. Achenes were susceptibl e to infection only at the time of their development, but symptoms wer e only visible just before physiological maturity. A field trial demon strated that western flower thrips (Frankliniella occidentalis) are as sociated with infection of the achenes. The effects of nine fungicides on disease severity were examined in two field trials in 1992. Althou gh some fungicides significantly reduced disease severity, their effec t was relatively minor and in general they were not highly effective.