2013 Annual Report
1a.Objectives (from AD-416):
Examine the effectiveness of differing colony densities on pollen transfer and almond nut set during the 2012 season.
1b.Approach (from AD-416):
Tests will be conducted near Bakersfield, CA, in cooperation with several almond growers, a prominent honey bee broker (Scientific Ag), and several beekeepers. Pairs of mature almond orchards will be matched for cultivar, tree age, and management practices. One orchard of each pair will be assigned either a high honey bee colony density or a low density. Orchards will be monitored for honey bee visitation rate, pollen transfer, pollination rate, nut set, and total yield.
We examined the impact of honey bee colony density on almond pollination. This was carried out on the same four ranches that were used in 2012 (near Bakersfield, CA). Both early and late varieties were tested on each ranch. Blocks of almonds were paired for variety, age, tree density, and management. One of the pairs had a higher number of colonies per acre placed in or around it prior to bloom. Nominal colony density differed between pairs of orchards by 0.5 to 1.0 colony per acre. Colonies in surrounding orchards out to 1.5 miles were counted and mapped. Their contribution of foragers to test orchards was predicted based on prior work involving the modeling of almond pollen foraging data near Bakersfiled, CA. Flower counts and video recordings of bee activity aided in interpreting pollination rates. A fifth, impromptu trial was initiated at the request of one of our cooperators. This involved an early variety orchard stocked with 0.5 colonies/acre. Pollination was monitored over a transect of diminishing colony density projections made by the model for this orchard.
With the exception of Sonora, all early varieties in orchards with higher colony densities had significantly higher pollination rates. Differences in percent pollination between low and high bee densities ranged from 1.5 to 18.4% (X=9.6%, n=13) for varieties Nonpareil, Fritz, Monterey, Sonora, and Aldrich. Significant increases in pollination occured in 92% of the paired early variety blocks. We did not detect a significant increase for the early variety Sonora, but availability of compatible pollen may have been a limiting factor.
With the exception of South Valley Farms, all orchards stocked with the higher colony density had significantly higher levels of pollination. Differences in percent pollination between low and high bee densities ranged from 5.7 to 18.4% for varieties Butte, Padre, and Mission. On South Valley Farms, we found a significant decrease in pollination for the high density, late variety orchard. The colonies on this pair of orchards were of poor quality. and many of the hives were empty. We suspect the poor level of pollination in these two orchards is due to this.
The harvestable nut count from the pollination trial was done in early August and will be reported at the December 2013 meeting. Commercial nut harvest has yet to be done. Determining the impact that differing pollination rates may have had on harvest will be reported later.