What research has been done on berries in South Africa? We summarise the published papers and postgraduate theses produced over the past four decades.
A literature search and emails to technical advisers yielded 24 papers and theses, the first of which appeared in 1982. The others are all post-2000, and 15 are from the last ten years (Figures 1 and 2). This growth in scientific output mirrors the expansion of the South African berry industry.
An early study (Meyer and Prinsloo, 2003) evaluated the potential of various areas in South Africa for commercial blueberry production, considering factors such as chill units and soil types. A subsequent MSc thesis (Fourie, 2022) discusses drivers and impacts of the rapid increase in South African blueberry production since 2015.
Whereas Meyer and Prinsloo focused on identifying suitable areas for blueberry production, Fourie found that financial and market factors motivated adoption. Blueberry production was also a good option for diversifying existing fruit-growing operations.
The remaining 22 papers, summarised below, are grouped into five categories: pollination, horticulture, pests, diseases, and postharvest. A reference list is provided at the end of this article.
Pollination
Blueberries can set fruit without insect pollination, but pollinators significantly increase fruit size and mass. Large bees, such as bumblebees, are the most effective pollinators of blueberries, but bumblebees do not occur in South Africa.
Martin and co-workers (Martin et al., 2021, 2022) compared the efficacy of honeybee pollination with hand pollination and an unpollinated control in Emerald, Eureka, Snowchaser, Suziblue, Twilight, and Ventura blueberries. The honeybee treatment had 15 hives per hectare.
Honeybees significantly increased yields (a combination of set and mass) compared to the unpollinated controls. Pollinated fruit also ripened faster than unpollinated fruit. However, hand pollination tended to give better yields and faster ripening than honeybee pollination. The authors reported substantial differences in cultivar responses to pollination.
In addition, Martin and co-workers (Martin et al., 2024) compared self-pollination to cross-pollination using different combinations of Emerald, Eureka, Snowchaser, Suziblue, and Twilight blueberries. They found that self-pollination can significantly reduce fruit mass and delay ripening, but the effects are cultivar-specific, and not all cultivars are equally cross-compatible.
Previous trials by Müller and co-workers (Müller et al., 2013) had similar results. They examined cross-pollination in Bluecrisp, Emerald, Jewel, and Snowchaser, and included Misty and Star as cross-pollinators.
Horticulture
Besides studying pollination, Müller (Müller, 2011) conducted pruning trials on Emerald, Jewel, and Star blueberries. He observed that summer pruning reduced total yield but increased berry mass and diameter and developed better bearing wood. He reported the details of pruning severity and timing in older and younger plants in his MSc thesis.
An MSc study (Kritzinger, 2014) investigated the fertigation of Emerald and Snowchaser blueberries by relating carbohydrate and macronutrient content of plants to their phenology. Measurements were done for two seasons. Her thesis includes fertilisation recommendations.
The 2020s saw two publications (Steyn et al., 2023, 2024) and an MSc thesis (Steyn, 2022) on the growth dynamics of two southern highbush blueberry cultivars in the Western Cape. Steyn described the above- and below-ground phenology and measured carbohydrate allocation patterns.
All these studies are important for understanding blueberry behaviour in South Africa, as our climatic conditions differ considerably from their native habitat.
For example, blueberries are grown in some South African regions with insufficient winter chill, resulting in delayed bud break and extended harvest periods. An MSc project (Swart, 2015) assessed whether chemical rest-breaking agents and light manipulation could facilitate harvest scheduling.
Hydrogen cyanamide and thidiazuron were applied to Bluecrisp, Emerald, and Star blueberries, and night interruption was tested in Emerald and Snowchaser for two seasons. The results suggest that hydrogen cyanamide may be safe and effective for some cultivars under specific conditions.
Blueberries rely on root-associated fungi to access soil nutrients. Three root-associated fungi from South African ericas were tested to see whether they could form symbiotic relationships with Brightwell and Misty blueberries (Bizabani et al., 2016).
All three fungi could colonise blueberry roots, but the colonisation percentage was low. However, the fungi improved root biomass in Misty, so inoculating blueberry plants with cultivar-specific root-associated fungi could benefit them.
Pests
Blueberry bud mites dominate the limited research on South African blueberry pests. This North American native was first discovered in South Africa in 2014 on blueberries in Mpumalanga (Craemer, 2018). Heavy mite infestations reduced flowering and fruiting.
A revised description of blueberry bud mites was recently published (Ngubane-Ndhlovu et al., 2024). The lead author on the study also documented other arthropod pests in cultivated blueberries for her MSc (Ngubane, 2018).
She found that pest and beneficial arthropods peaked in warmer months. Predator and parasitoid numbers were inversely correlated with plant feeders, suggesting that beneficials contribute to control. In addition, plant feeders were equally abundant in organic and conventional fields, which led her to question the efficacy of chemical pest control.
The banded fruit weevil was the other pest featured in South African blueberry research (Bredenhand et al., 2010). These insects damage a wide range of plants and fruit and have phytosanitary implications. Whereas tree fruit are monitored using cardboard bands, Bredenhand and co-workers found this to be ineffective in blueberries.
Instead, the authors reported that optimal monitoring in blueberries involves going out at night, placing a tray under a blueberry bush, and lightly beating the bush to dislodge weevils that then drop into the tray.
The most recent work on blueberry pests is a BerriesZA-funded project conducted by MSc student Zion Jodamus under the supervision of Prof. Pia Addison of the Department of Conservation Ecology and Entomology at Stellenbosch University.
Jodamus surveyed blueberry fields in different production areas. The project ended this year.
Diseases
The oldest berry publication in this literature review describes the isolation of raspberry bushy dwarf virus from commercially cultivated youngberries (Kooyman et al., 1982). This virus can reduce fruit yields and quality in blackberries, raspberries, and their close relatives.
Other publications include the first South African reports of a blueberry rust pathogen (Mostert et al., 2011) and of three oomycetes that cause stunting and leaf scorch in blueberries (Jami and Botha, 2023). Oomycetes are microorganisms that superficially resemble fungi.
Postharvest
The banded fruit weevil was the subject of an MSc study (Duvenhage, 2013), which demonstrated that postharvest irradiation could potentially control these phytosanitary pests.
Subsequent postharvest research on blueberries has been co-funded by BerriesZA. This includes the development of cold-sterilisation treatments for fruit flies (Anonymous, 2021) and registration trials for fludioxonil and pyrimethanil (unpublished).
Two recent publications (Foster et al., 2023, 2024) on botrytis in commercial blueberry production are outputs of an ongoing research project.
The results and practical implications of BerriesZA-funded projects will be shared in the Berry Brief as these become available.
References
Anonymous. 2021. Cold treatment: improving blueberry exports. SAFJ 20(3) pp96–99.
Bizabani C, Fontenla S, and Dames JF. 2016. Ericoid fungal inoculation of blueberry under commercial production in South Africa. Scientia Horticulturae (209) pp173–177.
Bredenhand E, Van Hoorn A, May F, Ferreira T and Johnson S. 2010. Evaluation of techniques for monitoring banded fruit weevil, Phlyctinus callosus (Schöenherr)(Coleoptera: Curculionidae), infestation in blueberry orchards. African Entomology 18(1) pp205–209.
Craemer C. 2018. First record, current status, symptoms, infested cultivars and potential impact of the blueberry bud mite, Acalitus vaccinii (Keifer)(Prostigmata: Eriophyidae) in South Africa. Acarologia 58(3) pp735–745.
Duvenhage AJ. 2013. An assessment of the potential of irradiation as a postharvest control treatment against the banded fruit weevil, Phlyctinus callosus (Coleoptera: Curculionidae): effects on adult weevils and host fruit (‘Flavor Fall’ pluots). (MSc thesis. Stellenbosch: Stellenbosch University.)
Foster B, Wilson I and Jacobs K. 2023. First report of potential multiple fungicide-resistant Botrytis cinerea in South African blueberry orchards. (Preprint).
Foster BJ, Wilson I and Jacobs K. 2024. First report of Botrytis cinerea in South African blueberry orchards. Journal of Plant Diseases and Protection (131) pp1731–1738.
Fourie M. 2022. Exploring the social-ecological drivers and impacts of the blueberry boom in South Africa. (MSc thesis. Stellenbosch: Stellenbosch University.)
Jami F and Botha W. 2023. Pythium and related species on blueberry plants in South Africa. Journal of Phytopathology 171(11–12) pp754–759.
Kooyman P, Engelbrecht DJ and Kasdorf GGF. 1982. Isolation of raspberry bushy dwarf virus from youngberry in South Africa. In III International Symposium on Small Fruit Virus Diseases (129) pp59–62.
Kritzinger H. 2014. Seasonal patterns in carbohydrates and macronutrients in southern highbush blueberry plants. (MSc thesis. Stellenbosch: Stellenbosch University.)
Martin K, Anderson B, Minnaar C and De Jager M. 2021. Honeybees are important pollinators of South African blueberries despite their inability to sonicate. South African Journal of Botany (137) pp46–51.
Martin K, Anderson B, Minnaar C and De Jager ML. 2022. Assessing the effectiveness of honeybee pollinators for cultivated blueberries in South Africa. South African Journal of Botany (150) pp113–119.
Martin K, Anderson B, Minnaar C and De Jager M. 2024. Inter-fertility of five highbush blueberry cultivars and ideal crossing combinations. The Journal of Horticultural Science and Biotechnology (10 December 2024) pp1–11.
Meyer HJ and Prinsloo N. 2003. Assessment of the potential of blueberry production in South Africa. Small Fruits Review 2(3) pp3–21.
Mostert L, Bester W, Jensen T, Coertze S, Van Hoorn A, Le Roux J, Retief E, Wood A and Aime MC. 2010. First report of leaf rust of blueberry caused by Thekopsora minima on Vaccinium corymbosum in the Western Cape, South Africa. Plant Disease 94(4) pp478–478.
Müller JL. 2011. Pruning and pollination studies on southern highbush blueberries (V. corymbosum L. interspecific hybrids). (MSc thesis. Stellenbosch: Stellenbosch University.)
Müller JL, Steyn WJ and Theron KI. 2013. The effect of cross-pollination of southern highbush blueberries on fruit set and fruit characteristics. Acta Horticulturae (1007) pp571–578.
Ngubane NP. 2018. Distribution of pests of blueberries in South Africa and re-description and behaviour of the blueberry bud mite Acalitus vaccinii (Eriophyidae) (MSc thesis. Stellenbosch: Stellenbosch University.)
Ngubane-Ndhlovu NP, Dhanani I, Roets F and Saccaggi DL. 2024. Revised description of the blueberry bud mite, Acalitus vaccinii (Acari: Trombidiformes: Eriophyidae), and a key to all Eriophyoidea on Vaccinium. African Entomology (32) pp1–12.
Steyn J. 2022. Investigating plant growth dynamics of selected southern highbush blueberry (V. corymbosum L. interspecific hybrids) cultivars under South African growing conditions (MSc thesis. Stellenbosch: Stellenbosch University.)
Steyn J, Lötze E and Hoffman EW. 2023. The seasonal progression of the reproductive phenology of two southern highbush blueberry (V. corymbosum L. interspecific hybrids) cultivars in the Western Cape, South Africa. Scientia Horticulturae (307) p111493.
Steyn J, Hoffman EW and Lötze E. 2024. Root growth dynamics of two southern highbush blueberry (V. corymbosum L. interspecific hybrids) cultivars in the Western Cape, South Africa. Scientia Horticulturae (336) p113344.
Swart P. 2015. Harvest scheduling of southern highbush blueberries (Vaccinium corymbosum L. interspecific hybrids) in a climate with moderate winter chilling. (MSc thesis. Stellenbosch: Stellenbosch University.)
