When Should Hives be Released from Almond Orchards?

Every year in California’s Central Valley, during January and February, the world’s greatest pollination event takes place. More than two million hives from around the U.S. are loaded on flatbeds and trucked out West to pollinate more than one million acres of almond orchards. The hives stay in almond orchards until growers release them — usually around mid-March — and they either journey homeward or off to pollinate another crop.

Pollination is an important part of growing almonds. Releasing hives from the orchard too early could result in reduced yields. Keeping them in the orchard too long can delay beekeeper’s other commitments and could result in risks for honey bee health. The details and timing of releasing bees from orchards should be discussed between the beekeeper and grower before bloom starts, with the understanding that weather conditions — such as this year's warm and dry February — could mean the hives are ready to be removed from the orchard earlier than predicted.

This article will clarify growers’ questions regarding the ideal time to release hives from orchards and explain a simple test that anyone can use to determine if flowers are still ripe for pollination, or if they are no longer able to set nuts.

Questioning pollination productivity? Use the anther test

The official University of California recommendation for hive removal, which aligns with that in the Almond Board of California’s Honey Bee Best Management Practices, is to release hives when 90% of the flowers on the latest blooming variety are at petal fall stage.^1,2 However, knowing whether a variety is at this stage can be tricky as there is no tool or test that unequivocally determines a particular variety has reached 90% petal fall. Still, if growers think their orchard has reached 90% petal fall they can work to verify their visual observations by reading the flower’s anthers.

Determining if flowers still have pollen and are receptive to cross-pollination is fairly simple: Anthers with pollen appear yellow and fuzzy, and for about four days there will be a mixture of opened (dehisced) and unopened anthers in the flower. Older anthers without pollen are dry and light brown, and in older flowers when none of the anthers have pollen they are no longer receptive to pollination.² Checking if the flower’s anthers have pollen can be determined through one simple test: Rub the flower’s anthers across a white piece of paper or roll them between your fingers. If viable pollen is present a smear of yellow will easily appear (as shown in the photo below) and if pollen is not present, as in older flowers with brown and dry anthers, no yellow residue will appear. Growers and beekeepers should use this test in each orchard to determine when the bees’ work is done and determine the best day to release hives.

Observe other contributing factors

When temperatures reach above 55⁰F, pollen is released by the flower’s ‘male’ parts, called anthers. This process is referred to as dehiscing. Then, the stigma, or ‘female’ part of the flower, is viable and receptive to pollination for only five days after dehiscing.³ In most cases, petals remain on flowers past the receptive period, so without a close inspection one might incorrectly assume that all open flowers visited by bees are still viable to accept pollen and be fertilized.

Furthermore, bee activity on flowers does not necessarily mean pollination is taking place, as the flower can still provide nectar but not pollen. Nectar-collecting bees are foragers with the sole purpose of harvesting the sugary carbohydrates from the flowers. These bees descend on the petals and only target the nectar at the base of the flower, rarely picking up or transferring pollen. Conversely, pollen-collecting bees are foragers that seek out the protein in pollen. They land directly on the anther and transfer pollen to the stigma surface, thus completing the process of pollination.

Ultimately, if pollen is not being produced — regardless of if petals are present — bees are no longer serving a purpose for growers by fertilizing their crop. Growers and beekeepers should work together to determine when it makes most sense to remove bees from the orchards, not only to preserve the best interest of the honey bees but also to best promote a healthy almond crop.

For more information on hive removal, check out the Almond Board’s Honey Bee Best Management Practices at Almonds.com/Pollination. And, to learn more about Project Apis m. and the research they support to enhance honey bee health, visit www.projectapism.org.

This article was contributed by Billy Synk from Project Apis m. in 2019 and updated by Dr. Josette Lewis in 2020.