Why Is My Blueberry Dropping Fruit Before It Ripens?

Finding small green or half-coloured blueberries on the ground under your bush is discouraging when you were expecting a good harvest. Premature fruit drop is the plant's way of shedding fruit it cannot support, and the cause is almost always a stress event that happened weeks before the berries hit the ground. Understanding when the drop occurs and what was happening to the plant at that time points you to the real cause.

June drop — natural thinning

A moderate amount of berry drop in early summer is completely normal. The plant sets more fruit than it can fully develop and then naturally aborts the weakest ones in what gardeners call June drop. This is similar to the June drop seen in apples. If the berries falling are the smallest and you are still left with a reasonable number of normal-sized developing fruit, no action is needed. The plant is managing its load.

Drought stress during fruit set

If the drop is heavy and the remaining berries look stressed or small, drought is the most common culprit. Blueberries that dry out during the critical weeks between petal fall and harvest abort developing berries to conserve resources. Check the soil — if it is dry below the mulch, water immediately and deeply. Blueberries should never be allowed to dry out between flowering and harvest. A consistent deep watering and a generous mulch layer are the two most effective ways to prevent drought-driven drop.

Spotted wing drosophila

If the berries dropping are nearly ripe or just starting to colour, and you find small white larvae inside the fallen fruit, spotted wing drosophila (SWD) is the cause. Unlike other fruit flies, SWD females can lay eggs into firm, ripening fruit using a serrated ovipositor. The larvae develop and the fruit softens and falls. SWD is increasingly widespread and can devastate a late-ripening crop. Soft mesh fruit cage netting with very small apertures provides physical protection. Harvest promptly as berries ripen and remove fallen fruit immediately to break the pest cycle.

Stem and bunch diseases

Mummy berry and anthracnose infections attack the stem connecting clusters to the branch, causing whole clusters to drop or individual berries within a cluster to shrivel and fall. If the fallen berries are shrivelled, mummified or show sunken dark spots, disease is the cause. Remove all fallen fruit, prune out affected wood and clean up the area thoroughly, as spores overwinter in fallen mummies on the soil surface.

Poor pollination

Poorly pollinated flowers may initially set a tiny berry but abort it within a few weeks as the undeveloped seed provides insufficient hormonal signal to sustain growth. If drops occur very early and the fallen berries are tiny and hard, poor pollination is likely. Adding a second compatible variety and fostering bumblebee populations in the garden is the long-term solution.