Is the mechanical application of pollen a last ditch effort to avert crop disaster or an insurance plan to ensure high nut set? The answer depends on the almond grower asked the question.
Each year, Elizabeth Fichtner, University of California Cooperative Extension farm advisor at Tulare County, says several almond growers try the mechanical application of pollen, fearing conditions were not just right for a good nut set.
Insufficient hive numbers or strength, or wet, cold weather conditions during bloom are reasons some growers consider mechanically applying pollen in their orchards.
Fichtner says achieving a higher nut set may not be a good enough reason to supplement bees.
“There are not enough carbs in the tree to support 100 percent set. In commercial orchards with adequate pollination, typical nut set is around 30 percent,” she said.
The timing of the application and pollen quality are two major considerations with mechanically-applied pollen.
There are two different approaches to the application: blowing pollen on trees with a blower or fixed-wing aircraft; or inserts of pollen dispensers into hives.
The first method relies on bee activity to redistribute pollen since only a small amount of blown pollen will be deposited directly on receptive stigmas. Research studies have shown no benefit from this method as a supplement to bee pollination on nut yield when Nonpareil rows are spanned on either side by pollinizer trees.
Fichtner noted another study conducted by Robin Thorp at UC Davis in 1978 that illustrated the benefit of an application of supplemental pollen. However, the study was conducted in an orchard with four solid rows of Nonpareil. This orchard design is no longer utilized in the industry.
Pollen inserts have been found to work in some situations but not in newer plantings. The Journal of Apicultural Research notes that pollen dispensers did not increase fruit set percentage or yield in a 1:1:1 planting design – pollinizer rows planted on either side of the main cultivar rows – with good bloom overlap.
The dispensers increased fruit set and yield in an orchard design with one pollinizer row, two Nonpareil rows, and one pollinizer row as bloom overlap was lacking.
In contrast to bee activity which lasts over the entire bloom period, mechanical pollination is a one-time event and only has the potential to pollinate a fraction of the flowers open at the time of the application.
Fichtner confirmed that the 2014 replicated field trial to determine the potential benefit of mechanical pollination, as a supplement to bee activity, did not significantly affect nut set or yield.
A 2015 trial with the Monterey variety suggested a benefit of mechanical pollination on nut set compared to bee exclusion. The exclusion achieved only a 1.3 percent nut set while mechanical alone resulted in 17 percent set. A combination of bees and mechanically-deposited pollen resulted in a 57 percent set as measured in May.
Fichtner said the potential exists for mechanical pollination to set a small crop in the absence of bees, but the decision might rest more on the economics of the practice. The cost for an application by blower was reported at about $300 per acre in 2016.
There are also practical considerations. Wet conditions that keep bees from working the orchards can also cause access issues for mechanical pollination machinery.
Terra Bella beekeeper Roger Everett noted it is difficult to determine if bee colonies did a good job of pollination until it is almost too late for mechanical supplementation.
He predicted sufficient hive numbers and strength for almond pollination in 2017, but probably not surplus hives. Increase in almond acres has not been offset by orchard removals, he said, keeping hive rental prices steady in recent years.
The current recommendation is for 1.5 colonies per acre although insurance companies may require two colonies per acre. Depending on frame numbers per colony, 2017 hive rental cost is expected in the $170-$200 range.
The 2017 almond bloom period will see increased demand for hives due to the increase in commercial acres. Acre numbers are slightly offset by the removal of older orchards in high water cost areas, said bee broker Joe Traynor of Bakersfield.