EFFECT OF FLORAL DEBRIS REMOVAL FROM FRUIT CLUSTERS ON BOTRYTIS BUNCHROT OF CHARDONNAY GRAPES

The relationship between senescent floral debris retained in fruit clu sters and the incidence and severity of botrytis bunch rot was examine d in Chardonnay grapevines over three seasons. Floral debris was remov ed from clusters at either early or late fruit set using compressed ai r or a back-pack leaf blower. Additional treatments were included to d etermine if a commercial sticker spray adjuvant (Nu-Film 17) increased debris retention in clusters. Physical removal of floral debris gener ally reduced botrytis bunch rot; however, reductions in botrytis bunch rot were only significant in some vineyards. The sticker spray adjuva nt had no effect on retention of debris or on botrytis bunch rot. The incidence and severity of botrytis bunch rot were not affected by timi ng of debris removal, but late removal by compressed air, when berries were as much as 8 mm in diameter, did cause berry bruising. The data demonstrate that senescent floral debris and aborted berries can contr ibute to increased botrytis bunch rot, and that practical measures to reduce debris retention may aid disease control.