Supplemental Pollination - What we (don't really) know

I had a few questions this week about supplemental pollination to increase the amount of compatible pollen available for almonds. Mainly, the growers were asking about the feasibility of increasing compatible pollen in orchards with only one pollinator variety or in orchards with greater than 50% Nonpareil.Here was what I was able to dig up:Research:- Work conducted by Robbin Thorp determined that application of supplemental pollen by modified ground rig, helicopters and beehive inserts did not increase fruit set or yields in orchards with adequate cross pollinating varieties;- However, a 2006 study by Tom Gradziel indicates there may be benefit when using hexane washed pollen (removes sticky pollenkit and the pollen does not clump) dispensed at the hive entrance. In this experiment, trees were caged and pollen parentage was tracked. They found that 6% of the almonds were pollinated with the washed pollen.Comments:In many of the older trials, pollen sourced for the experiment had questionable viability. It is important to know if the pollen is viable and able to germinate, form a strong pollen tube, and fertilize the almond embryo. Pollen viability is not the only limiting factor; stigma receptivity also affects nut set. This is why flowers are the most receptive to pollen within the first few days after opening and explains why an extended bloom usually means a reduce crop.It may be reasonable to try to provide extra pollen, delivered by honey bees, when there is no other variety providing overlapping bloom. It is important to note that it is extremely difficult to determine if the extra pollen improves crop production. Studies (paternity tests) have demonstrated that supplemental pollen is able to fertilize the embryo in orchards where they have been applied. Then again, how can you prove that those nuts would not have set with the available local pollen?Isolated plantings, and plantings with poor pollinator overlap, may benefit from extra pollen. We, the UC, just do not have the science yet to answer this question definitively. For growers considering adding pollen to your orchard, it may be wise to experiment with differing blocks or sections of your orchards.