Blueberries: Although the acreage is small in Ohio, blueberries (high bush) need bee pollination, sometimes at a rate of 2 to 5 colonies per acre with unattractive cultivars. This is especially true in large acreages.
Some beekeepers in New Jersey and Michigan have experienced high rates of European foul brood, a disease of bee larvae, after renting bees on blueberries. The cause is not known and may make beekeepers reluctant to move bees into blueberry fields. Beekeepers might reduce the European foul brood problem by not moving the same colonies into blueberries year after year.
Figure 10. Honeybees cross pollinate self-sterile fruit varieties through their visiting from one tree to another and by transfer of pollen when rubbing against each other in the colony.
Strawberries: The homeowner and small producer rarely have a problem of pollination of strawberries due to the presence of a few native bees and honeybees which find the flowers rich in nectar and pollen. But in expanded acreages such as is becoming more common, there is often a considerable need for pollination.
Research in strawberry pollination, conducted in Michigan, revealed that (1) many large commercial fields were nearly devoid of bees, (2) a number of varieties benefited substantially from bee pollination, and (3) some varieties were not attractive to bees because of low nectar and/or pollen production. Consequently, while some strawberry fields may need no rental colonies, others need only 1 colony for every 2 to 4 acres, and others might require 2 or 3 colonies per acre. When there is doubt, bees should be provided at the rate of 1 colony per acre and adjusted in later years according to yield records.
Fortunately, there is a way growers and beekeepers can check strawberry flowers for completeness of pollination. In flowers just completing bloom ( evidenced by falling petals and bending of the flower stem ), a change takes place in the appearance of the pistils on the flowers. If the pistils were pollinated, they will appear dark and shrunken in size. But if they were not pollinated, they will appear yellow-green and fresh in appearance. Thus, a partially pollinated strawberry flower will have a mottled appearance at this stage. Often, only the pistils at the tip of the flower will be unpollinated.
If poorly pollinated flowers are evident in your field, additional bees may be useful to improve the yield of the crop. Remember, however, that the flowers already past bloom will not be visited by bees, so you will still have a certain number of poorly shaped berries in the first few pickings.
There is some indication that blackberries and raspberries have a range of variability of pollination needs similar to strawberries.