Wild blueberries go through a series of developmental stages before producing a harvestable berry. These stages extend over a two-year period, or production cycle, consisting of a sprout and crop year. During these two years, wild blueberry floral buds undergo three dormancy periods before bud burst and bloom, the flowers then need to be pollinated and germinated, and the seeds need to be fertilized. Read this week’s blog to get an overview of these processes and what is needed to get harvestable wild blueberries.

Wild Blueberries - From Dormant Buds to Ripe Berries

This journey starts with the first dormancy period known as paradormancy. During paradormancy the apical meristem, the growth region at the tip of the stem, has dominance over the lower or lateral meristems, where the floral buds will form [4]. During the fall of the first year, or sprout year, short daylength and cold temperatures drive tip-dieback, or apical abortion. Once apical dominance is broken, then the floral buds can form. The buds then enter a second dormancy period known as endodormancy, which helps the buds survive harsh winter conditions [4]. The buds will acclimate throughout endodormancy as temperatures get colder [1]. This stage can be measured by an accumulation of cold temperatures, known as the chilling requirement. The chilling requirement of wild blueberries is approximately 1000 hours of temperatures less than 0°C [7]. The floral buds will then enter the third dormancy period known as ecodormancy, which prevents the buds from opening too early in the spring [4]. The floral buds deacclimate throughout ecodormancy as the temperatures rise [1]. This stage can be measured by an accumulation of daily mean temperatures, known as growing degree days (GDD). It takes approximately 400 GDDs for the start of bloom, with peak bloom happening around 550 GDDs [6].

Endodormant wild blueberry floral buds (John MacDonald ©, 2024)

Once all three dormancy periods are satisfied, the floral buds will start to burst and these can be measured by the five stages of bud burst, known as T1 to T5 [3].  The T1 stage is known as the bud swell stage when the buds start to expand, and a green tip can be seen. The T2 and T3 stages are known as the early bud burst and bud burst stages, respectfully, when the buds continue to swell and the bud scales are separating. The T4 stage is known as the tight cluster stage when flower pedals become visible and elongated. Finally, the T5 stage is known as early flower which is just before bloom when the flowers are still closed. The next stage is floral bloom when the flowers have fully opened.

The stigma, where the pollen lands on the receiving flower, on individual flowers is only receptive to pollen for up to nine days, where pollination within the first four days will result in the highest fruit set [2]. The bloom period for an entire field is typically three to four weeks [2]. Wild blueberry fields typically contain two species of wild blueberries, Vaccinium angustifolium and Vaccinium myrtilloides, and pollination is incompatible between these species. Wild blueberries are also self-incompatible, so wild blueberry flowers require pollen transfer from a different clone of the same species to get successfully pollinated [2].

Pollination can be one of the most limiting factors in wild blueberry fruit production. Pollination is the transfer from pollen from the anther of one flower to the stigma of another flower on a different clone of the same species. Wild blueberries are entomophilic with respect to pollination, meaning that they need an animal pollinator [2]. The conditions during bloom need to be ideal for the animal pollinators to ensure successful pollination. Wild pollinator populations vary between fields, so managed pollinators are used to get even pollination. Therefore, placement and removal of managed pollinators is crucial in providing efficiencies around pollination.

Bumblebee pollinating wild blueberry flowers (John MacDonald ©, 2024)

Once the pollen is successfully transferred from the anther of one plant to the stigma of another clone of the same species the next stage, known as pollen germination, can start. If conditions are favorable for the flowers, germination typically starts two to three hours after successful pollen transfer [5]. During germination, a pollen tube forms into the ovary at the base of the style, or female flower parts, and extends to an individual ovule. The pollen sperm travels down the pollen tube until they reach the ovule. Pollen germination can take three to four days, if conditions are favorable [5]. The next stage is known as fertilization, when the pollen sperm reaches the eggs and nuclei they are fertilized, and the seeds start forming. Once the seeds are formed, the fruit starts developing around the seed which provides protection and helps with seed dispersal. There are different maturity stages of blueberries from pin head, to green, to red, and then to ripe blue harvestable fruit.

For more information on how to tell if a flower was successfully pollinated, please check back in for the next blog on wild blueberries.

Written by John MacDonald, ATTTA Seasonal Apiculturist

Connecting with ATTTA Specialists

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

Email attta@perennia.ca

References:

[1] Deslauriers, A., Garcia, L., Charrier, G., Butto, V., Pichette, A., and Pare, M. 2021. Cold acclimation and deacclimation in wild blueberry: Direct and indirect influence of environmental factors and non-structural carbohydrates Agricultural and Forest Meteorology, 301–302: 108349. (ACCLIMATION)

[2] Drummond, F. 2019. Reproductive biology of wild blueberry (Vaccinium angustifolium Ait.). Agriculture, 9(4): 69.

[3] Hildebrand, P.D., and Braun, P.G. 1991. Factors affecting infection of lowbush blueberry by ascospores of Monilinia vaccinii-corymbosi. Canadian Journal of Plant Pathology 13(3): 232–240.

[4] Lang, G.A., Early, J.D., Martin, G.C., and Darnell, R. 1987. Endo-, para-, and ecodormancy: physiological terminology and classification for dormancy research, Horticulture Science, 22(3): 371–377.

[5] Noormets, M., and Olson, A.R. 2005. Observations on the gynoecial pathway for pollen tube growth in sweet lowbush blueberry (Vaccinium angustifolium Ait.), Journal of Applied Botany and Food Quality, 80: 6-13.

[6] White, S.N., Boyd, N.S. and Van Acker, R.C. 2012. Growing degree-day models for predicting lowbush blueberry (Vaccinium angustifolium Ait.) ramet emergence, tip dieback, and flowering in Nova Scotia, Canada, Horticulture Science, 47(8): 1014–1021.

[7] Yarborough, D.E. 2012. Establishment and management of the cultivated lowbush blueberry (Vaccinium angustifolium), International Journal of Fruit Science, 12(1–3): 14–22.

Pollination is the transfer of pollen from the male to female plant reproductive organs which leads to germination and fertilization of seeds. The resulting fruit helps to protect the seeds and helps with their dispersal. Through evolution plants have adapted to ensure successful reproduction by pollinators and pollinators have adapted to use flowers as a resource for growth and reproduction. This week’s blog discusses wild blueberry pollination and flower ecology, and why pollination can be so difficult.

Wild Blueberry Flower Ecology

Plants have flowers for sexual reproduction, to produce new plants with genetic material from both parents. In the wild blueberry industry, the focus on flowers is fruit production. Wild blueberry flowers contain both male and female reproductive organs, stamens and pistils respectively. The female organs contain a stigma for receiving pollen, at the end of a style, with ovaries at the base. The male organs contain pollen on an anther, at the end of a filament. The flower parts like petals and sepals help to protect the reproductive tissues throughout pollination, germination, and fertilization. Since plants are immobile, they need wind, water, or animals to transfer pollen. Wild blueberries require animal pollination due to their flower structure [3]. Therefore, there is a mutual relationship between flowers and pollinators, which is reproductive success of the plant in exchange for nectar and pollen for the animal.

Figure 1: Honey bee pollinating wild blueberry flower (ATTTA ©, 2024)

About 90% of flowering plants use animal pollinators for reproduction. There are more than 130,000 species of animal pollinators, containing more than 25,000 species of bees [5]. Wild blueberry flower pollination is generalized, meaning most flowers receive many kinds of pollinators, and the flowers do not specialize in the needs of the best pollinator [5]. This benefits the plant because pollinator populations and biodiversity can vary in different areas, visiting times may be different between pollinators, and weather conditions may not be ideal during bloom for certain pollinators. So, attracting many pollinators will allow for more effective pollination. From the pollinator’s perspective, it does not want to be a good pollinator; it just wants the resources the flower provides. Therefore, only about 1% of all pollen successfully reaches the stigma [5].

Plants have many ways of attracting pollinators to help with reproduction. These include, but are not limited to, individual flower or whole plant characteristics, attractants, and rewards. Individual flowers can display colors (including ultraviolet colors which humans cannot see), different shapes, and timing of flowers opening. Whole plants can vary in density, number, height and pattern of flowers. Attractants include visual and olfactory cues, and rewards include nectar and pollen availability. It is in the plants’ best interests to support pollinators or improve pollinator efficiency, such as ensuring the pollinator visits the necessary flowers. The plant can do this by changing color, odor, or shape after the flower is successfully pollinated, to prevent wasted effort of the pollinators [5].

Attractants are an efficient way to lure pollinators, but they can also attract unwanted visitors. If there is not an effective transfer of pollen from the anther to the stigma, then the pollinator is known as an illegitimate visitor or cheater. Therefore, measuring pollination success should not be done by only observing the number of animal visitors to flowers. There are more precise ways of identifying pollinator success, such as single visit deposition on virgin flowers [2]. ATTTA has also done many studies where fruit set and the number of viable seeds is counted after pollination to determine pollination success [1].

Figure 2: Wild blueberry bloom (ATTTA ©, 2024)

Plants and animals have a competing interest, which has led to adaptation and counteradaptation through evolution. Both parties want a larger share of resources for growth and reproduction. An ideal pollinator, from the plant’s perspective, is one that is cheap to feed, stops briefly, moves rapidly to another plant of the same species, and is faithful to that species. The ideal flower, from the pollinator’s perspective, is one that provides lots of nectar or pollen, which requires spending less energy [5]. An example of this in wild blueberries is the adaptation of the poricidal anthers [3], which allows slow pollen release and prevents loss of pollen due to eating. The bumblebee has adapted to this with buzz pollination [4], which is sonication to help shake large amounts of pollen from poricidal anthers. Plants use resources to provide attractants and rewards, and if the plant reduces these too much then the pollinator will likely not be interested in visiting. Plants must compete with other plant species for the best pollinators to ensure successful reproduction and the plant also must offset costs with cheaters or flower eaters that are inadvertently attracted.

Pollination ecology is important because it provides insights into evolution, animal learning, forage behavior, biological processes and patterns, and evolution by natural selection [5]. The wild blueberry industry has a higher demand than supply for pollinators, so understanding flower ecology and pollinator behavior can help provide efficiencies around wild blueberry pollination.

Written by John MacDonald, ATTTA Seasonal Apiculturist

Connecting with ATTTA Specialists

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

Email attta@perennia.ca

References:

[1] Bennett, A. and A. Byers. 2023. Best management practices guide for honey bee pollination of wild blueberries in Atlantic Canada. Atlantic Tech Transfer Team for Apiculture.

[2] King, C., Ballantyne, G. and Willmer, P.G. 2013.Why flower visitation is a poor proxy for pollination: measuring single-visit pollen deposition, with implications for pollination networks and conservation. Methods in Ecology and Evolution 2013, 4: 811–818.

[3] Orr, J., Byers, A., Morandin, L.A., Medeiros, S.J. and K. Law. 2023. Practices to protect pollinators from pesticides: wild blueberry. Pollinator Partnership Canada and Atlantic Tech Transfer Team for Apiculture.

[4] Vallejo-Marin, M. 2018. Buzz pollination: studying bee vibrations on flowers. New Phytologist 2019, 224: 1068-1074.

[5] Willmer, P. 2011. Pollination and flower ecology. Chapter 1: why pollination is interesting. Princeton University Press.

Wild blueberries are managed on a two-year production cycle, meaning that the plants need to grow for two years for a harvestable crop. During this time, wild blueberry floral buds need to go through three dormancy stages before flowering. Please see previous blogs for more detailed information on the first two dormancy stages, para- and endo- dormancy. Once the blueberry buds have met their para- and endo-dormancy requirements they can enter ecodormancy, which is normally late winter to early spring. Once ecodormancy requirements have been met, then the buds will flower. Wild blueberry producers currently use ecodormancy requirements, based on growing degree days (GDD), to try and predict when the buds will open, and pollinators are needed in the fields. Knowing the requirements that are needed for ecodormancy could help with predicting wild blueberry bloom and allow for more precise placement of managed pollinators for more efficient use of this limited resource.

Wild Blueberry Phenology in the Crop Year - Ecodormancy

Ecodormancy is the second winter dormancy stage of floral buds, where the reaction leading to growth control is driven by external environmental cues, such as warm temperatures⁵. Ecodormant buds will not flower normally, meaning that only some of the buds will open when placed in growth adequate conditions, and the ones that do open will take longer to do so. Ecodormancy will prevent the floral buds from opening until the growing conditions are adequate for flowers, therefore protecting them from fluctuating conditions in the spring. Ecodormancy release relies on an accumulation of warm temperatures and the most common way of measuring the accumulation of warm temperatures is with GDDs⁵.

Ecodormant wild blueberry floral buds in early Spring (© John MacDonald 2024)

GDDs are a measure of accumulated daily heat units during which the plant has potential to be physiologically active and is measured using daily mean temperatures¹. Accumulations of heat units for ecodormancy begin when endodormancy is released. Currently, there are limited experimental results for when endodormancy is released for wild blueberries. Therefore, GDD accumulations for ecodormancy begin at a selected calendar date³, which is currently April 1^st for wild blueberries. Most GDD models include a base and upper temperature threshold, specific to different organisms, at which development may be delayed due to unfavorable growing conditions³. GDD models can be used to predict many crop phenological events, such as pest life cycles for applications of pesticides and floral bloom for placement of pollinators.

GDD models have been created in Nova Scotia to predict phenology of weeds, such as yellow toadflax (Linaria vulgaris), spreading dogbane (Apocynum androsaemifolium), and red sorrel (Rumex acetosella)^2,9,10. GDD models have also been created for predicting flowering in highbush and lowbush blueberries^4,6. More specifically, wild blueberry ramet emergence, tip-dieback, and flowering prediction models have been created in Nova Scotia⁸. The existing model for wild blueberry flowering, however, requires revisions to include early flowering wild blueberry genets and the timing of endodormancy release.

Wild blueberry field during ecodormancy in early Spring (© John MacDonald 2024)

Perennia Food and Agriculture Corporation, Nova Scotia’s technical food development agency, currently has an application called Farm Weather on the Farm Data Tools Website.  This tool will easily calculate GDD accumulations at weather stations, including 55 on wild blueberry fields, throughout Nova Scotia. Please make an account on Farm Data Tools and check out this very useful resource (Farm Data Tools – Farm Data Tools).

The placement of pollinators on wild blueberry fields during bloom can be difficult to plan. Learning more about the phenology stages of wild blueberries, such as endo- and eco-dormancy requirements, may help to create predictive models for the placement of pollinators. These models, based on GDD, could allow more efficient use of managed pollinators, improve wild blueberry production, and support honey bee health.

Written by John MacDonald, ATTTA Seasonal Apiculturist

 

Connecting with ATTTA Specialists

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

Email abyers@perennia.ca

 

References:

1. Baskerville, G.L. and Emin, P. (1969) ‘Rapid Estimation of Heat Accumulation from Maximum and Minimum Temperatures’, Ecology, 50(3), pp. 514–517. Available at: https://doi.org/10.2307/1933912.

2. Blatt, S., De Clerck-Floate, R. and White, S.N. (2022) ‘Development of a growing degree-day model to estimate Linaria vulgaris shoot emergence and prospects for improving biological control efforts’, Invasive Plant Science and Management, 15(1), pp. 9–15. Available at: https://doi.org/10.1017/inp.2022.6.

3. Carlson, J.D. and Hancock, J.F. (1991) ‘A Methodology for Determining Suitable Heat-unit Requirements for Harvest of Highbush Blueberry’, Journal of the American Society for Horticultural Science, 116(5), pp. 774–779. Available at: https://doi.org/10.21273/JASHS.116.5.774.

4. Kirk, A.K. and Isaacs, R. (2012) ‘Predicting Flower Phenology and Viability of Highbush Blueberry’, HortScience, 47(9), pp. 1291–1296. Available at: https://doi.org/10.21273/HORTSCI.47.9.1291.

5. Lang, G.A. et al. (1987) ‘Endo-, Para-, and Ecodormancy: Physiological Terminology and Classification for Dormancy Research’, 22.

6. NeSmith, D.S. and Bridges, D.C. (1992) ‘Modeling Chilling Influence on Cumulative Flowering: A Case Study Using `Tifblue Rabbiteye Blueberry’, Journal of the American Society for Horticultural Science, 117(5), pp. 698–702. Available at: https://doi.org/10.21273/JASHS.117.5.698.

7. Rieger, M. (2006) Introduction to Fruit Crops. Haworth Food & Agricultural Products Press.

8. White, S.N., Boyd, N.S. and Van Acker, R.C. (2012) ‘Growing Degree-day Models for Predicting Lowbush Blueberry (Vaccinium angustifolium Ait.) Ramet Emergence, Tip Dieback, and Flowering in Nova Scotia, Canada’, HortScience, 47(8), pp. 1014–1021. Available at: https://doi.org/10.21273/HORTSCI.47.8.1014.

9. White, S.N., Boyd, N.S. and Van Acker, R.C. (2015) ‘Temperature Thresholds and Growing-Degree-Day Models for Red Sorrel (Rumex acetosella) Ramet Sprouting, Emergence, and Flowering in Wild Blueberry’, Weed Science, 63(1), pp. 254–263. Available at: https://doi.org/10.1614/WS-D-14-00048.1.

10. Wu, L. et al. (2013) ‘Spreading Dogbane (Apocynum androsaemifolium) Development in Wild Blueberry Fields’, Weed Science, 61(3), pp. 422–427. Available at: https://doi.org/10.1614/WS-D-12-00156.1.

Successful pollination of wild blueberry crops is dependent on managed pollinators. Studying phenology stages throughout the life cycle of wild blueberry crops could help with efficiencies around the use of these pollinators. Time between emergence and tip dieback in the sprout year will determine what the stem can support in the crop year.  Evaluation of these phenology stages could support a prediction model, using sprout year data, for the numbers of pollinators required in the crop year. Wild blueberry phenology stages in the crop year include two winter dormancy periods, known as endodormancy and ecodormancy, as well as flowering, fruit set, and harvest. With a better understanding of the dormancy periods of wild blueberries, a prediction model for timing of bloom and pollinator placement may be determined earlier in the crop year to help with pollinator efficiencies.

Wild Blueberry Phenology in the Crop Year - Endodormancy

Endodormancy is the first of two winter dormancy periods that are needed for wild blueberry buds to resume normal growth in the spring, and it is driven by internal cues within the plant [5]. Wild blueberry buds become endodormant to withstand cold temperatures and dehydration and prevent buds from opening throughout the winter when growth conditions are not adequate. Endodormancy is initiated by cold temperatures late in the summer and short daylength helps to accelerate this process. Cold temperatures in the fall also help acclimatize the buds to withstand freezing temperatures throughout the winter [1,6]

Endodormant wild blueberry plants (©John MacDonald 2024)

There are many changes happening internally when the buds go endodormant, including but not limited to the bound-to-free water status and hormone levels. The water goes from a free state to a bound state with macromolecules when the buds go endodormant. Also, the two most important hormones that are related to dormancy are abscisic acid (ABA) and gibberellin (GA). There is an increase in ABA within the plant during the initiation of endodormancy, which suggests that ABA plays an important role in endodormancy initiation. There is an increase in GA and decrease in ABA during endodormancy release, suggesting that GA plays an important role in endodormancy release [7].

The release of dormancy is regulated by the accumulation of cold temperatures, which is known as the chilling requirement. This can be calculated as chilling hours, which is an accumulation of temperatures between a lower and upper threshold (e.g., between 0 and 7°C) [3]. In contrast, chilling unit models are created to consider the reduced efficacy of temperatures below or above an optimum value and hence account for the reduced or negative effects of certain temperatures. The chilling requirement of wild blueberries is estimated at 1000 hours of temperatures less than 0°C [9,12], but limited results are available to confirm this assumption.

Endodormant buds will have a delayed and reduced growth rate compared to non-dormant buds when placed in growth adequate conditions, therefore dormancy must be satisfied to have adequate flowering and fruit set [10]. Knowing the chilling requirement for endodormancy release can give insight into the timing and intensity of bloom. The state of dormancy in wild blueberry floral buds can be determined by sampling floral buds throughout the winter, while the buds are receiving more chilling hours, and evaluating them in a greenhouse or laboratory.

One way dormancy release can be evaluated is a change in water status or hormone levels using intricate laboratory techniques. Another simpler and cheaper method that will yield similar results is known as forcing buds in a greenhouse. This is done by observing the rate of buds opening after a determined amount of time [4,8,11] or observing the number of buds opening after a determined amount of time [2,7]. Dormancy release is considered to have occurred when plants exposed to more chilling hours exhibit similar rates of buds opening.

Endodormant wild blueberry plants (©John MacDonald 2024)

After endodormancy is released, we then have ecodormancy, flowering, and fruit set. Currently wild blueberry producers and beekeepers use April 1st as an approximation of when endodormancy is released and ecodormancy starts in the Maritimes. This is inaccurate as the accumulation of chilling hours or units will vary from year to year, based on endodormancy requirements. Therefore, determining when endodormancy is released in wild blueberries will give a better approximation as to when flowers will open and help with efficiencies in placing pollinators for optimal fruit set.

Check back in the following weeks for part two of Wild Blueberry Phenology in the Crop Year – Ecodormancy and Flowering.

Written by John MacDonald, ATTTA Seasonal Apiculturist

 

Connecting with ATTTA Specialists

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

Email abyers@perennia.ca

 

References:

[1] Deslauriers, A. et al. (2021) ‘Cold acclimation and deacclimation in wild blueberry: Direct and indirect influence of environmental factors and non-structural carbohydrates’, Agricultural and Forest Meteorology, 301–302, p. 108349. Available at: https://doi.org/10.1016/j.agrformet.2021.108349.

[2] Ferlito, F. et al. (2021) ‘Assessment of chilling requirement and threshold temperature of a low chill pear (Pyrus communis L.) germplasm in the Mediterranean area’, Horticulturae, 7(3), p. 45. Available at: https://doi.org/10.3390/horticulturae7030045.

[3] Fraisse, C.W. and Whidden, A. (2010) ‘Chill accumulation monitoring and forecasting’, Electronic Data Information Source, 2010(AE452). Available at: https://doi.org/10.32473/edis-ae452-2010.

[4] Guak, S. and Neilsen, D. (2013) ‘Chill unit models for predicting dormancy completion of floral buds in apple and sweet cherry’, Horticulture, Environment, and Biotechnology, 54(1), pp. 29–36. Available at: https://doi.org/10.1007/s13580-013-0140-9.

[5] Lang, G.A. et al. (1987) ‘Endo-, para-, and ecodormancy: physiological terminology and classification for dormancy research’, HortScience, 22(3), pp. 371–377.

[6] Li, C., Junttila, O. and Palva, E.T. (2004) ‘Environmental regulation and physiological basis of freezing tolerance in woody plants’, Acta Physiologiae Plantarum, 26(2), pp. 213–222. Available at: https://doi.org/10.1007/s11738-004-0010-2.

[7] Li, Y. et al. (2022) ‘Comparative transcriptomic analysis provides insight into the key regulatory pathways and differentially expressed genes in blueberry flower bud endo- and ecodormancy release’, Horticulturae, 8(2), p. 176. Available at: https://doi.org/10.3390/horticulturae8020176.

[8] Norvell, D.J. and Moore, J.N. (1982) ‘An evaluation of chilling models for estimating rest requirements of highbush blueberries (Vaccinium corymbosum L.)’, Journal of the American Society for Horticultural Science, 107(1), pp. 54–56. Available at: https://doi.org/10.21273/JASHS.107.1.54.

[9] Rieger, M. (2006) Introduction to fruit crops. Haworth Food & Agricultural Products Press.

[10] Schuchovski, C. and Biasi, L.A. (2021) ‘Dormancy of floral buds of rabbiteye blueberry in a mild winter climate’, Brazilian Archives of Biology and Technology, 64, p. e21190755. Available at: https://doi.org/10.1590/1678-4324-2021190755.

[11] Spiers, J.M., Marshall, D.A. and Braswell, J.H. (2004) ‘Chilling requirement studies in blueberries’, Small Fruits Review, 3(3–4), pp. 325–330. Available at: https://doi.org/10.1300/J301v03n03_09.

[12] Yarborough, D.E. (2012) ‘Establishment and management of the cultivated lowbush blueberry (Vaccinium angustifolium)’, International Journal of Fruit Science, 12(1–3), pp. 14–22. Available at: https://doi.org/10.1080/15538362.2011.619130.

Wild Blueberry Phenology in the Sprout Year

Wild blueberries are managed on a two-year production cycle. The reproductive growth in the second, or crop, year relies on the vegetative growth in the first, or sprout, year to support the development of flowers and fruit. Wild blueberry plants are pruned to promote new vigorous stem growth. The emergence of new stems is driven by warm temperatures in the spring and is controlled by apical dominance, meaning the tallest growing point has dominance over the lower growing points, and will grow upright. The time between emergence of these new stems and when tip-dieback occurs in the fall will determine what the stem can support in the crop year. When the tip dies, the buds are released from dormancy and differentiate to floral buds. With greater knowledge on these stages of the blueberry life cycle, we may be able to predict, in the sprout year, how many flowers the plants will produce and how much fruit these may yield.

Wild Blueberry Phenology in the Sprout Year

Wild blueberry plants are perennial, so they survive for many years. When left alone, the stems will grow taller and will branch more every year. Taller stems with more branches use more resources for vegetative growth.  Therefore, reproductive growth will receive less resources on older stems, resulting in fewer flowers, smaller and less fruit. Wild blueberry producers overcome this through managing the plants on a two-year production by pruning stems after harvesting. By pruning the plant, new growth is stimulated from the underground stems, known as rhizomes. The first year of growth will only be vegetative, but this growth will support the reproductive growth (flowers and fruit) in the second year. 

Pruning wild blueberry plants promotes growth of young vigorous stems, with less branching, and will allow the plant to put more resources into flower and fruit development, resulting in more flowers and greater fruit set. Pruning to a uniform height also allows for more efficient use of farming equipment, such as fruit harvesters and pesticide sprayers. Naturally wild blueberries respond to events such as wildfires through stimulated rhizome growth resulting in increased fruit production. Producers mimic these natural events by burning or mowing crops maintaining a two-year production cycle. Flail mowing is currently the most common practice for pruning wild blueberries.

Flail mower pruning wild blueberry field (credit unknown)

When new stems arise from the rhizome, they have apical dominance. This means that the tallest growing point on the plant has dominance over the lower growing points. Therefore, the buds are in a dormant state, called paradormancy [1]. Abortion of the apical growing point in wild blueberry is a prerequisite to flower bud initiation in the sprout year. Therefore, the time between ramet emergence and tip dieback is crucial in terms of establishment of both crop density and biomass that will support the development of flower buds in the bearing year [2]. Tip-dieback is regulated by short daylength, so during shorter days in late summer, the highest growing point dies, the buds are released from dormancy, and floral buds are formed. The next stages of the wild blueberry plant include leaf cessation, endodormancy, and acclimatizing to winter conditions.

Evaluation of wild blueberry stems during emergence and tip-dieback, during the sprout year, may be the earliest point at which we could determine the number of flowers and fruit wild blueberry stems can support, during the crop year. By learning more about these phenology stages and determining what may be the best duration of time between emergence and tip-dieback for best fruit and flower production, we may be able to make earlier decisions on pollination numbers. If an estimation can be made in the sprout year on how many pollination units may be needed in the crop year, blueberry producers and beekeepers could make earlier decisions and use pollination units more efficiently.

In the coming weeks, the blog will include more information on winter dormancy and wild blueberry phenology stages in the crop year to help predict when to place pollination units. 

Written by John MacDonald, ATTTA Seasonal Apiculturist

Connecting with ATTTA Specialists

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

Email abyers@perennia.ca

References:

[1] Lang GA, Early JD, Martin GC, Darnell RL. 1987. Endo-, para-, and ecodormancy: Physiological terminology and classification for dormancy research. 22.

[2] White SN, Boyd NS, Van Acker RC (2012). Growing Degree-day Models for Predicting Lowbush Blueberry (Vaccinium angustifolium Ait.) Ramet Emergence, Tip Dieback, and Flowering in Nova Scotia, Canada. HortScience 47(8):1014-1021.