Blueberries are vulnerable to pests when not treated with an insecticide. However, not all untreated blueberries have worms. Fruitworms, in particular, attack blueberry bushes and lay eggs on foliage and stems. Once hatched, larvae burrow into berries where they feed on their flesh. For this reason, home gardeners frequently spray bushes before fruit set to eliminate worms and protect crops.
Cranberry and cherry fruitworms infest blueberry bushes, and feed on blueberries and shoots. Adult moths lay eggs on the bush. Once eggs hatch, tiny worm-like larvae infiltrate young berries and cause premature ripening. Inside the berry, the larvae mature into adult worms of about 3/5-inch in length. Depending on the specific type of worm, they can either be greenish-yellow, as the case of cherry fruit worms, or pinkish-red, like cranberry worms. Both types of worms, however, destroy blueberry crops in identical ways, and similar control applications are used to rid cranberry and cherry worms from berries.
Chemical Control Spray
Spray a low-toxicity insecticide, such as an insect growth regulator, on blueberry bushes after bud formation and before fruit set. Ideally, you want to time the application to coincide with when larvae hatch from their eggs. It's at this phase of development that larvae are most affected by the insecticide. If you wait until the larvae have hatched, the spray is likely to have less of an impact on worms since they will have already entered the berry.
Aside from spraying blueberry bushes, biological control is probably the next best defense against worms. Parasitic wasps prey on fruitworms and naturally eliminate them from blueberry plants. Create an environment that lures wasps to blueberry bushes to help keep worm populations down. For example, place a bird feeder filled with water near blueberries, vary your garden design and avoid spraying insecticides that discourage wasps from visiting blueberry bushes.
Home gardeners are sometimes reluctant to spray blueberry bushes to prevent worms because chemical insecticides are poisonous to animals and humans if digested. Always thoroughly wash blueberries before eating them to remove chemicals and dirt. Spray bushes early in the morning, so not to disrupt bees from pollinating buds. Bees generally are more apt to pollinate blueberry bushes in the afternoon rather than the morning when temperatures are cooler. While you don't have to spray blueberry bushes, it's basically the best method for controlling worms. If you choose not to spray, inspect blueberries for worm damage before eating them. Discard blueberries that show signs of disease and decay.