Why Are My Grapes Falling Off Before They Ripen?

Individual berries dropping from the bunch before harvest is an alarming sight, but it is worth distinguishing between normal physiological drop, which is a natural self-thinning process, and pathological drop caused by disease or pest damage. Examining the dropped berries and the bunch closely will usually tell you which you are dealing with. Once the cause is identified, the appropriate response — whether that is a fungicide treatment, improved watering consistency, or simply accepting the vine's natural thinning — becomes clear.

Post-set berry drop — normal thinning

Shortly after fruit set in early summer, grapevines naturally abort a proportion of their berries, particularly those that were incompletely fertilised. You will see small, green, hard berries dropping from the bunch — this is entirely normal and actually improves the final bunch by concentrating resources into the remaining well-fertilised fruit. No action is needed unless the drop is very severe (leaving almost nothing on the bunch).

Botrytis (grey mould) causing pre-harvest drop

Botrytis cinerea infection at the berry or bunch stem causes individual berries to soften, collapse, and drop as the fungus digests the fruit tissue. If the dropped berries are soft, grey-furred, or show shrunken skins with visible mould, botrytis is the cause. Remove affected bunches, improve canopy ventilation, and apply a suitable fungicide (such as a product based on fenhexamid or pyrimethanil) at the earliest sign of infection.

Inconsistent watering causing physiological drop

A period of water stress followed by a heavy soaking — or the reverse — can cause the berry stems to form a sudden abscission layer, dropping berries much as a drought-stressed tree might drop fruit early. Keep soil moisture as consistent as possible through the growing season using mulch and regular but moderate irrigation. Erratic watering is especially problematic for container-grown vines.

Wasp and bird damage

Wasps and birds do not usually cause berries to fall — they eat them in place — but heavy feeding can dislodge individual berries from the bunch. If berries are disappearing rather than found intact on the ground below, wildlife is the likely culprit rather than disease or physiological drop.

Black rot infection

Black rot (Guignardia bidwellii) causes berries to shrivel and turn black before they ripen, and affected berries may fall from the bunch. Look for small circular brown spots with darker margins on the leaves and berries at the same time. Black rot spreads in warm, wet conditions and needs a preventative fungicide programme to control it effectively.