Hello. The mentioned symptoms (small, shrivelled fruit) can be caused by one or more abiotic or biotic factors: high temperatures during this period, long exposure to sunlight, low humidity in the soil, inadequate soil pH, possibly a phytopathogenic disease (moniliosis) etc.
In this case, to be on the safe side, it is recommended to remove heavily affected berries and treat them with a fungicide such as , in a dose of 10 g/10 L water, applied by uniform spraying on the plants.
Subsequently, in order to stimulate the healthy growth of the plants and implicitly of the fruits, in addition to a good water supply, a balanced fertilization is also essential. Therefore, it is recommended to use a fertilizer with the purpose of revitalizing and stimulating the growth of the plants: , by watering at the roots, according to the recommendations on the label.
For more information on the proper care of blueberries, you can check our article: https://www.armuro.com/en/blueberry-planting-growing-harvesting.