Many times each year the question is asked: “How early can I remove the bees from my almonds without jeopardizing potential production?” Some will argue that once you are past 80% to 90% petal fall there is very little crop set. Others will argue that they are leaving the bees in until the last flowers are gone as each blossom represents a potential nut.
In 2010, I was asked this many times, and I can recall while working for the University of California (UC) Cooperative Extension, being asked that question numerous times, as well. This past spring provided a perfect opportunity to conduct an experiment to address this question for several reasons. First, the inclement weather provided a challenging situation for the bees to pollinate. Second, the late almond bloom overlapped into subsequent pollinating requirements for other crops, so many beekeepers were anxious to move hives out while almonds were still in bloom. Third, with hive rentals hovering in the $125 to $150 range, and up to three hives per acre, growers were very conscious about keeping their investment working as long as possible.
To evaluate this concern, I took a late blooming Butte/Padre block (since they are most likely to conflict with cherry/apple requirements) and took 15 tree paired replications of each variety. I waited until the trees were well into petal fall, and tagged limbs that still had buds in pink bud to popcorn stage. Care was taken to count only unopened blossoms.
The grower still had hives present (2.5 hives per acre) during the experiment (started March 16). In late May, after any potential shedding, a percent set count was made of the sound nuts.
It should be noted that typically the first blossoms to reach petal fall are on the mid-outer section of the trees and on the weeping hangers. The last area where blossoms opened was on the upright upper-most shoots. These are the ones that were counted for this experiment.
The results of this test were quite revealing. Among the 15 paired Butte/Padre trees, the late-opening blossoms on the Butte averaged 56.4% set and the Padre 64.1%. This is substantially higher than the normal percent sets I have counted in experiments over the last 30 years, both at UC and independently. Typically Nonpareil is in the 22% to 28% set range in a normal year, and pollenizers range from 30% to 45% with the late varieties being amongst the higher percentages. Are these 2010 numbers the norm or an aberration? I suspect that since bloom weather was affected by rainfall this year, and many of the first blossoms to open may not have set, the precocity of the later flowers may have increased. This could explain why the sets are higher than normal.
Although this is only a one-year study, it does illustrate the potential benefit of having bees present until the trees are finished blooming to maximize yield potential. I realize that percent set is only part of the equation, since the total number of late opening flowers on the tree will ultimately determine whether there is an economic advantage to leaving bees in until the end of bloom. That is a decision the grower needs to make on a case-by-case situation.