Wild blueberry producers rely on managed pollinators, such as honey bees, to successfully pollinate their crops. Successful pollination depends on many factors, such as weather conditions, pollinator availability, pollinator health, and proper placement of pollinating units. Many plant phenology stages are dependent upon weather conditions, such as dormancy and flowering, so with more knowledge about these phenology stages we may be able to make early predictions for pollination requirements. Stocking density predictions could potentially be done in the fall of the sprout year and hive placement could be determined long before flowers are opening in the fields in the crop year.
Understanding Plant Phenology to
Increase Pollination Efficiency
Wild blueberries are grown on a two-year
production cycle. The first year is called a sprout year and the second year is
called a crop year (Jenson & Yarborough 2004). The blueberry plants grow
vegetatively, meaning only stems and leaves, for most of the sprout year. The highest
growing points on the stem have dominance over the lower growing points and the
lower buds are dormant which is known as paradormancy (Lang et. al 1987). When
day length is shortened in the fall, the tip of the plant dies, known as tip-dieback,
and the lower growing points are then released from dormancy to become either
floral or leaf buds (Barker & Collins 1963). This may be the earliest point
at which the amounts of floral buds can be determined and therefore provide an
estimate of how many flowers there will be in the crop year. Since stocking
density is determined based on the number of flowers, this could be used as the
earliest point to determine stocking density of pollination units.
Wild blueberry floral buds go through a
winter dormancy to be able to prevent freezing and drought damage. The winter
dormancy happens in two stages, endodormancy and ecodormancy (Lang et. al 1987).
Endodormancy requires an accumulation of cold temperatures to satisfy. This is
known as the chilling requirement and can be measured by chilling hours, which
are an accumulation of temperatures between 0-7C (Fraisse & Whidden 2010).
Ecodormancy requires an accumulation of warm temperatures to satisfy, and this
can be measured by growing degree days, which are an accumulation of daily mean
temperatures (Baskerville & Emin 1969). Once both dormancy stages are
satisfied, then the floral buds will open and flower.
Endodormant wild blueberry buds (©John MacDonald 2024)
Wild blueberries are self-incompatible,
meaning that they do not self-pollinate and rely on a pollinator to cross
pollinate with other plants (Reiger 2006). The flowers are only receptive to
pollen for eight to ten days after opening, but fruit set rapidly declines four
days after flowers open (Drummond 2019). Native pollinators do provide some of
the pollination services needed but blueberry producers rely on managed
pollinators, such as honey bees and bumblebees to effectively pollinate their
crops (Cutler et. al 2012; Bushmann & Drummond 2015). Placement of
pollination units at 10 to 20% of the fields total bloom is optimal for good
fruit set, with pollination success quickly declining quickly after 50%
(Bennett & Byers 2023). Therefore, creating a bloom prediction model will
help improve placement of pollination units, so that growers can use this very
valuable but limited resource more efficiently.
Honey
bee foraging wild blueberry flowers (©ATTTA 2023)
As the wild blueberry season unfolds, we
will be presenting a short series on how a better understanding of plant
phenology can allow us to more efficiently apply managed insect
pollinators. Check back in for more
information over the next few weeks.
Written by John MacDonald, ATTTA Seasonal Apiculturist
References:
Barker WG, Collins WB. 1963. Growth and
development of the lowbush blueberry: apical abortion. Can J Bot.
41(9):1319–1324. doi:10.1139/b63-112.
Baskerville GL, Emin P. 1969. Rapid
estimation of heat accumulation from maximum and minimum temperatures. Ecology.
50(3):514–517. doi:10.2307/1933912.
Bennett A, Byers A. 2023. Best management
practices guide for honey bee pollination of wild blueberries in Atlantic
Canada.
Bushmann SL, Drummond FA. 2015. Abundance
and diversity of wild bees (Hymenoptera: Apoidea) found in lowbush blueberry
growing regions of down east Maine. Environ Entomol. 44(4):975–989.
doi:10.1093/ee/nvv082.
Cutler GC, Reeh KW, Sproule JM, Ramanaidu
K. 2012. Berry unexpected: Nocturnal pollination of lowbush blueberry. Can J
Plant Sci. 92(4):707–711. doi:10.4141/cjps2012-026.
Drummond F. 2019. Reproductive biology of
wild blueberry (Vaccinium angustifolium Aiton). Agriculture. 9(4):69.
doi:10.3390/agriculture9040069.
Fraisse CW, Whidden A. 2010. Chill
accumulation monitoring and forecasting: AE452/AE452, 1/2010. EDIS. 2010(1).
doi:10.32473/edis-ae452-2010. [accessed 2024 Feb 12].
https://journals.flvc.org/edis/article/view/118311.
Jensen KIN, Yarborough DE. 2004. An
overview of weed management in the wild lowbush blueberry—past and present.
Small Fruits Review. 3(3–4):229–255. doi:10.1300/J301v03n03_02.
Lang GA, Early JD, Martin GC, Darnell RL.
1987. Endo-, para-, and ecodormancy: Physiological terminology and
classification for dormancy research. 22.
Rieger M. 2006. Introduction to fruit
crops. Haworth Food & Agricultural Products Press