Spraying

At the moment, blueberries in the UK rarely suffer from any pests and diseases which require spraying. However, as the climate changes, especially as warmer, damper weather occurs fungal problems may increase. Some of the fungal problems which may occur are 'Mummy Berry' and Botrytis.
To control mummy berry, ensure the ground under your blueberry plant is throuroughly raked during the winter or before bud break in the spring. This helps to bury or destroy the 'mummy storage pods' which release the fungus.
To control Botrytis and to avoid stem canker, avoid over feeding with Nitrogen and prune out any canes showing dieback and ensure your pruning regime gets rid of dead twigs and branches during the winter.

In the US and some other areas of the world, potential insect problems could include blueberry tip borer, plum curculio, cranberry fruit worm, and cherry fruitworm. Disease problems include mummy berry, powdery mildew, twig blights, botrytis blossom blight, leaf spots, and cane gall.
Malathion is the most common pesticide available here for most of these problems.