Using bees for pollination of small fruit crops
Value of pollination
According to calculations by Calderone and Morse (2000), the value of honey bee pollination to agriculture in the United States is as high as $US 14.6 billion per year. In Michigan alone the total value to the main fruit and vegetable crops dependent on honey bee pollination is about $300 million per year. Bee pollination of small fruit crops provides the essential cross-fertilization of plants that promotes larger, earlier berries and increased percentage of fruit set.
Use the “late” strategy for small fruit crops
In general, flowers of small fruit crops are less attractive to honeybees than other flowers due to the shape and the relatively low “reward,” so a different strategy is required than you might use for apples, which need bees early. You want to have your crop starting to bloom before bringing bees in so that bees tend to forage more on your crop. If brought in too early, bees will learn to forage elsewhere and when your crops bloom, they are not attractive enough to get the bees “back” to where you want them. Blueberry flowers have about three days to be pollinated after the flowers open, but you want the bees to stay in the field, so move bees into blueberry fields after 5% bloom but before 25% percent of full bloom. The “late” strategy is especially important for cranberries, which is not very attractive to bees. Luckily, cranberry flowers will stay open for a while if not pollinated, and the petals will turn to a rosy color if not pollinated in time. In cranberries, it is better to wait until 10% bloom in order to maximize the yield. If you see too many flowers turning rosy, this means you did not have enough pollinators, so make sure you increase the number of bee hives next year.
Prices for pollination
Most growers will already have their pollination contracts set, but expect to pay anywhere from $40 to $70 per colony for spring fruit pollination. There is a range here because if you only need 10 hives, you might be expected to pay a higher price than the other grower who is renting 500 hives. Colonies might be also of different strengths. Try to deal with the same beekeeper year after year in your area so you know what to expect and can build a good working relationship. If the beekeeper is new in the pollination business, make sure he or she knows your requirements and make sure you sign an agreement for pollination purposes.
The invasion of Varroa mite has decimated the numbers of feral (unmanaged, wild) honeybee colonies that used to contribute to pollination in addition to rented colonies. The proportion of pollination caused by feral bees relative to managed colonies is unclear, but it is safe to say that we need higher densities today than when feral bees were present. Recommended densities of managed bees are three hives per acre for cranberries, and one hive per acre for strawberries and raspberries. Research in blueberries has shown variation in their needs for bee pollination. This is mainly because cultivars with short open flowers and good nectar production are easier to pollinate. Because of this, varieties like Rubel require one strong hive on two acres, whereas Jersey may benefit from increasing hive densities to five per acre. The average is around two hives per acre. In general, a good rule of thumb is that you’ll need four to eight bees per plant in the warmest part of the day during bloom to achieve good pollination.
Do not cut corners in respect to putting enough bees in your crops. Investing some money to have enough colonies there at the right time will provide returns in the form of improved yields.
If possible, place the colonies in a sheltered location with the entrances facing east. This will encourage earlier activity as the hive warms in the morning sun. Hives should be spread out around the field to maximize floral visitation, with a maximum of 300 yards between colonies.
Many other helpful insects are active in your fruit crop, and with 20,000 recorded species of bees worldwide, some local native bees are probably active in Michigan’s small fruit crops providing free pollination. Bumblebees and other native species can be seen looking for flowers already in and around fruit crops, and their activity generally remains high when weather conditions turn too cold or wet for honeybees. These native bees may be insufficient to provide adequate pollination for good yields, however, and cannot be relied on to stand alone as your sole pollination source. By providing the right nesting habitats and food for the bees after your crop has flowered, you can enhance the local populations of native bees around your crop. This is a long-term process and you’ll need several years of experimenting before these bees can become a reliable part of your pollination planning. Ongoing research at MSU is investigating strategies for conservation of native pollinators in Michigan blueberries, and we expect this work to be relevant to many other Michigan fruit crops.
Pest management during pollination
Do not apply broad-spectrum insecticides when flower buds are open or you may kill a significant number of pollinators. Bee hives should be removed immediately after pollination if post-bloom pesticide applications are planned. By monitoring for pest problems carefully during bloom, growers can help minimize the need for pest control. If an insecticide application is necessary during bloom, the compounds that are least toxic to bees should be used, with careful observation of the pollinator-restrictions on the label. Two insecticides that can both be applied during bloom for control of moth larvae in blueberry and cranberry are the Bacillus thuringensis (Bt) products, and the insect growth regulator tebufenozide (Confirm ®). Good coverage is required for both, and a spreader/sticker should be used to improve effectiveness. Inform the beekeeper two to three days before application so that precautions can be taken to minimize bee exposure. Evening application is better than morning application and in general liquid form is less harmful to bees compared to the powder form. More information and a list of chemicals with their toxicity to bees is available at http://www.beelab.osu.edu/factsheets/sheets/2161.html
Pollination information available online
Although it is a little outdated (first printed in 1976), the book “Insect Pollination of Cultivated Crop Plants” covers nearly all crops (fruits and vegetables) and is the best reference available for pollination to-date. It has been out of the print for many years, but the book is available free online at: http://gears.tucson.ars.ag.gov/book/. Other websites provide specific information on honeybees, native bees and pollination.