A blueberry bush is capable of setting fruit on 100 percent of the flowers, although 80 percent set is considered a full crop. Insects, especially bees, are required to obtain this high percentage of set.
Blueberry pollen is shed from pores in the anthers onto the bodies of bees that vibrate the flowers. The pollen is sticky and heavy, not easily transported by wind. Bumblebees and other specialized wild solitary bees are capable of “sonicating” or vibrating the pollen from the anther. Honeybees do not sonicate blueberry flowers and rarely collect much blueberry pollen.
Carpenter bees can be a problem during pollination as they pierce holes in flowers during nectar collection. Honeybees often feed through these holes and thus carry out no pollen in the process. This is especially a problem in flowers with long corollas (petals).
Flowers with short corollas are more easily pollinated than those with longer corollas. Some attribute the consistent fruit set of Bluecrop to its shorter corolla, and the poor set of Earliblue to its longer corolla. Cultivars also vary in their ability to attract pollinators. Earliblue, Stanley, and Coville are relatively unattractive to bees, whereas Rubel and Rancocas are more attractive. Evidence suggests that attractive cultivars produce more nectar than others.
Honeybees are not as efficient as bumblebees in pollinating blueberry flowers. They forage less when the temperatures are cool, the day is overcast, or the wind speed is high. Compared to wild bees and bumblebees, honeybees begin flying later in the morning and return to their hives earlier in the evening. Wild bees do not maintain much energy reserve in their nests, so must work for their food every day.
Maintaining dense native plantings along the perimeter of a planting will encourage nesting by wild bees and aid with pollination. However, wild bees cannot always be depended on for pollination because of inadequate or fluctuating population numbers.
One rule of thumb is that four to eight bees should be foraging on each blueberry plant at any one time during the warmest part of the day during bloom. When wild pollinators are not abundant, honeybees can be introduced.
Hives should be in place when about 5 percent of the flowers have opened, but no later than 25 percent full bloom, and they should remain until the petals begin to drop. One strong hive (minimum of 45,000 bees) is sufficient for 2 acres of Rancocas and Rubel; one hive per acre for Weymouth, Bluetta, Blueray, Pemberton, and Darrow; three hives for every 2 acres of Bluecrop; two hives per acre of Stanley, Berkeley, Coville, and Elliott; and five hives per 2 acres of Jersey and Earliblue. Competing flowers should be eliminated (e.g. mow the dandelions).
Hives should be placed in a wind-sheltered, sunny location with their entrances facing east. The bees will become active sooner if facing the morning sun.
Distribute the hives evenly throughout the field to maximize the probability of flower visitations. Bees fly further along rows than across them. Place hives 300 feet apart along every tenth row.
Growers should be aware of the importance of bees in blueberry culture and make every effort to protect honeybees and native bee populations. Never use insecticides during bloom. Fungicides, however, are relatively safe to use around bees. Refer to “Protecting Honey Bees from Pesticides” in the PNW Insect Control Handbook (see Bibliography ) for more information.
A pesticide-free source of water should be placed near the hives. Arrangements should be made with the beekeeper in advance to remove the hives before insecticide spraying resumes.
If fruit set is very poor, gibberellic acid sprays can be applied to increase set. This hormone induces parthenocarpic fruit set (seedless berries), but results in smaller, later maturing fruit.
This fact sheet is adapted from Oregon State University Extension Publication PNW215, Highbush Blueberry Production. The authors of Highbush Blueberry Production are – Oregon State University: Bernadine Strik, Glenn Fisher, John Hart, Russ Ingham, Diane Kaufman, Ross Penhallegon, Jay Pscheidt and Ray William; Washington State University: Charles Brun, M. Ahmedullah, Art Antonelli, Leonard Askham, Peter Bristow, Dyvon Havens, Bill Scheer, and Carl Shanks; University of Idaho: Dan Barney. PNW215, Highbush Blueberry Production can be purchased from the Department of Extension & Experiment Station Communications, Oregon State University. How to Order