Wild Blueberry Phenology in the Sprout Year

Friday 31 May 2024

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 (Lang et al. 1987). 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 (White et al. 2012). 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

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

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.