Historical Milestones, Current Methods, and Strategies Resulting in Year-Round Strawberry Production in Belgium

ABSTRACT

Strawberry production in Belgium has evolved from being a June-harvested crop grown in soil to a year-round crop grown in multiple production systems, as a result of the development of new cultivars and production techniques. Strawberry cultivation used to be one aspect of diverse family enterprises, but now strawberry farms are specialized. In the beginning, strawberries were only harvested in June. Covering the crop with plastic tunnels allowed the harvest to advance to May. Subsequently, an important innovation was the use of cold-stored plants in year-round plantings, which also allowed later production. This evolution in combination with the development of various cultivation systems using peat substrates (including table-tops, plastic greenhouses, and glasshouses) resulted in a strawberry production period from March until December–January. Recently, interest in assimilation lighting in glasshouses has increased. At first, this allowed advanced production in February, but now even winter production is possible, resulting in fresh Belgian strawberries 365 days a year.

KEYWORDS:

• Fragaria × ananassa
• plant storage
• tunnel cultivation
• soilless culture
• assimilation light

Concentration areas of strawberry production

In Belgium, the first strawberries were cultivated around 1880 in Pajottenland and Wépion (Figure 1). Strawberry plants coming from castle gardens found their way to farmers. The presence of the market in Brussels and local markets near Wépion made it a lucrative business to sell strawberries as a fresh product. In the “Noorderkempen” (Northern Campines) the first strawberries were grown around 1910. Just across the border in the Netherlands strawberry culture for processing was already practiced and expanded to Belgium. This region, Noorderkempen, experienced a technological evolution after the Second World War to become the most important strawberry production area in Belgium, with currently a lot of greenhouse production. Around 1980 strawberry culture also developed in Tongeren and Sint-Truiden, with mostly soil cultivation. Roeselare increased its production starting from 2000. From 1960, strawberry production in the southern part of Belgium declined because of excessive taxes, the absence of new cultivation techniques, and the possibility for other lucrative businesses.

Figure 1. Concentration areas of strawberry in Belgium (derived from map NGI, Brussel).

Currently, strawberry cultivation is concentrated in seven main locations in Belgium (Figure 1). Most locations are situated in the Northern part of Belgium: “Noorderkempen” (Hoogstraten) and “Waasland” with a lot of greenhouse production, “Haspengouw” (Tongeren, Sint-Truiden) with a lot of soil cultivation, and Roeselare, which recently became more important in the production of strawberries. “Pajottenland” near Brussels was an important strawberry production area in the past, but decreased over the last few decades. Wépion and Huy, situated in the southern part of Belgium, comprise only a small proportion.

Evolution in cultivars

Numerous different cultivars were grown from 1880–1955. Each region had their own cultivars and there was no cultivar that was dominating the cultivar segment. The cultivars Marguerite, Jucunda, Laxton’s Noble, Parisiène, Mme Moutot, Mme Lefeber, Tardive de Leopold, and Regina were grown in Wépion. Near Huy the cultivars Saint-Lambert, Triomphe de Liège, Ville de Paris, and Surprise des Halles were grown. In the Noorderkempen Jucunda, Talisman and Red Gauntlet were produced for the processing industry. In 1955 the cultivar Gorella was introduced, which was a productive cultivar with large berries of relative good quality. Together with some technological advances in protected cultivation systems, this cultivar made it possible to reach the milestone of producing strawberries for the fresh market. Besides Gorella, the cultivar Primella was suited for early production in glasshouses. Bogota, Tago, and Bavo were grown as late cultivars. Gorella dominated the cultivar segment in Belgium until 1985. In 1981, a second important change was made with the release of the cultivar Elsanta, a very productive and high-quality strawberry suited for all cultivation systems. Already in 1985, Elsanta dominated the cultivar segment in Belgium. Thirty years later, Elsanta is still the most important strawberry cultivar.

Since 2000 the early cultivar Darselect became more important in heated greenhouses and in tunnel cultures in soil. But because of the lower productivity of Darselect, it was replaced by newer cultivars in greenhouses from 2005. For tunnels in soil, cultivation techniques were optimized and Darselect was the main cultivar until 2010, but disappeared almost completely and was replaced by Elsanta. Since 2005, some new cultivars have been gaining their market share: first Sonata and a bit later Clery. These cultivars are grown now in the early glasshouse production and Sonata is also grown in the early open field production. From 2014 on, the short-day cultivar, Elegance, which is grown in the open field, became more important in the region of Haspengouw.

Mainly short-day cultivars were grown except for the region in Tongeren where Selva was important in the past. Recently, the everbearing cultivars—also referred to as “day-neutrals”—gain more and more interest. The spread out aspect of the price-risk and the harvest, together with the reduced labor, is one of the greatest advantages of growing the long-day cultivars. Currently, ‘Portola’ is the main everbearer in Haspengouw, grown in the open field. Presently in the Noorderkempen, new everbearing cultivars on substrate start to develop on several farms.

Cultivation techniques to improve out-of-season production

Little technical evolution occurred until 1945, prior to which most strawberries were grown in soil and the harvest period was limited to the months of June and July. The move towards more intensive professional cultivation was made after the Second World War (1940–45). In 1947, the School for Agri- and Horticulture was founded in the Noorderkempen to bring forth skilled people. In addition, the Research Centre Hoogstraten was established in 1955 to solve various cultivation problems. From then on, advances could be made and the technical evolution was directed towards prolonging the harvest season.

Advancing the harvest season was the first step. The development of different plastics covering crops made it possible to establish an earlier harvest period. The introduction of the high-quality cultivar Gorella also increased the percentage of strawberries destined for the fresh market. In the early 1960s, strawberries were grown in both plastic and glass greenhouses but all strawberries were still grown in soil.

Delaying the harvest season became possible thanks to the long-term cold storage of plant material, the development of substrate culture, and the introduction of cultivar Elsanta suited for almost every cultivation system.

At the end of the 1960s, short-term cold storage of 4 weeks was introduced. Plants harvested in November were planted in December. Owing to the knowledge of flower initiation and development, plants were also harvested later in December and remained in cold storage for 8 months. This long-term cold storage could delay the planting date. Greenhouses with heating capacities were able to create the desired climate thereby producing strawberries during autumn and the beginning of the winter season.

The substrate culture was developed together with the introduction of the nutrient film technique (NFT). NFT was a water culture technique in which plants were grown bare-rooted in a recirculation nutrient solution that flowed continuously in long horizontal gutters. Water experiments with hydroponics were carried out since the 1960s, but water culture has been used as a research tool in Germany during the late nineteenth century (Lieten, 1993). The NFT was introduced in 1970 and further adapted in the UK, Belgium, and Holland for strawberries in the late 1970s and early 1980s (Van Looy and Aerts, 1979). The cultivar Primella was grown for some years with NFT. In 1981 the very productive cultivar Elsanta, producing high-quality strawberries, was released. However, Elsanta is susceptible to Phytophthora cactorum and Phytophthora fragariae. The absence of effective disinfection and the sensitivity of Elsanta towards Phytophthora sp. was responsible for the rapid disappearance of NFT in Belgium and Holland. Instead, growers started cultivating strawberries on peat or coir as substrate.

Expanding the harvest period was responsible for the specialization of the family enterprises. Strawberry culture used to be a spring and summer activity that had to be completed, with another crop in autumn, such as tomato or gherkins. From now on, 100% of the income came from strawberries thanks to the longer harvest period in specialized family enterprises. This technological evolution also resulted in less strawberries produced for the processing industry. At the present time, most growers produce strawberries from March or April until the end of December or beginning of January. More than 90% is sold for the fresh market, so less than 10% of the total production is destined for the processing industry.

Commercial milestones for strawberry in Belgium

At first, growers sold their product to traders who sold the fresh product at the market. Strawberries from the Noorderkempen were brought to a growers’ cooperative across the border in the Netherlands. In 1932, the border was closed and in 1933 the first growers’ cooperative was established in the Noorderkempen in Belgium. This was the first milestone for the commercialization of strawberries in Belgium. Another important step was realized in 1985: the fresh product was classified according to standardized quality classification. Now, traders know exactly what they buy and growers receive money at the average price of each quality classification. At the same time, simultaneous tele selling was introduced. Strawberries were sold at different locations at the same time with a transparent selling system, known as clock selling. A product of a predefined quality was offered at the market and traders were invited to bid. The market could play, which was beneficial for the growers. A third important action was the cold storage of the fresh product. The growers’ cooperative cooled the fresh product to prolong the shelf-life of the product. From that point on, export of the fresh product became important.

Current methods and strategies of strawberry culture

The combination of different plantings in different cultivation systems results in a year-round production of strawberries in Belgium and Holland. An overview of the current cultivation methods and strategies is given in Figure 2.

Figure 2. Common cultivation methods and strategies to produce strawberries in Belgium almost year round. With assimilation lighting there is also production in January–February.

Soil cultivation

The “traditional” August planting in soil is carried out with fresh plants to harvest the strawberries the following year in June. Fresh plants are planted at a density of 4 plants.m^–2 on plastic beds and result in an average yield of 2.5–3.5 kg.m^–2. The crop can also be covered with plastic tunnels from winter (November until January) until harvest, which advances the main production to May. This system yields about 3–4 kg.m^–2 net tunnel surface.

Another system is to work with cold stored plants, namely, bare rooted waiting bed plants. In August, fresh plants are planted on a waiting bed for a better development until dormancy is achieved in December. The plants are then lifted from the soil and put in cold storage, until planting from April to June at 4 plants.m^–2. The harvest period starts mid-June until mid-September for the earliest and latest planting dates, respectively. The average yield in this system is 2.5–3.5 kg.m^–2 for the early plantings and 2.0–2.5 kg.m^–2 for the later plantings. When planted in the first half of July, these crops have to be covered with plastic tunnels when the harvest begins and harvest is possible until mid-October.

Table top systems

Table top systems are production systems (support structures for substrate pots or substrate containers) that are an alternative for in-soil production. This soilless substrate culture is still expanding due to increased restrictions on use of soil fumigants (Lieten, 2013) and to produce strawberries protected for precipitation. The period of harvest is similar to the open field production. The most common plant density is 12 plants per linear meter, but the distance between the table top rows varies from 1.15 to 1.4 m, which gives an assortment of plant densities from 8.5 to 10 plants per square meter. Plantings are established from mid-March to early July, with harvest beginning between June and mid-August depending on planting date. Yield for early plantings are around 4.0–5.5 kg.m^–2, for late plantings around 3.0–4 kg.m^–2. Two plantings can be achieved on table-tops, with a first planting in March and a second planting in early July. The second planting must use a waiting field where the pots or containers stay under sprinklers after planting, until harvest of the first crop on table tops is finished. When the first crop is removed from the table tops, the plants are replaced with those from the later planting. Currently, most table top systems are covered with small tunnels (row by row) or larger tunnels (multiple rows). For all of the substrate cultures mostly tray plants are used as plant material. These are substrate grown plants that are cold stored with the substrate they are grown in.

Plastic greenhouse production

In unheated plastic greenhouses, cold stored plants of ‘Elsanta’ are planted in February–March (9 to 10 plants.m^–2 on substrate). Production starts in early May and continues to June, and usually yields up to 4.5–5.5 kg.m^–2. A second planting is carried out mid-July and is harvested from September to mid-October. The second crop yields about 3.5–4.0 kg.m^–2.

A second possibility is to plant in July and to overwinter the plants after the autumn crop. Flower induction in autumn will result in a second harvest in May and June. During the winter months, it is important to protect the plants against frost damage by placing the pots on the ground and covering them. In mild to warm winters, breaking of dormancy might be difficult. Therefore, a long-day treatment with artificial cyclic lighting for 4 weeks can reduce or solve this problem. A second possibility is to overwinter plants in cold storage; therefore, controlling temperature to get enough chilling (Stoffels et al., 2014). Independent of the overwintering method, a double-cropping system in a plastic greenhouse of about 5.5 to 6.5 kg.m^–2 can be harvested in spring.

Glasshouse production

Glasshouse production is all on substrate nowadays. The most common system in the heated glasshouse is a double-cropping system. A planting between 10 Aug. and 25 Aug. with ‘Elsanta’ trayplants at 10–11 plants.m^–2 gives a first harvest from the end of September until the end of December or early January. About 3.5–4.5 kg.m^–2 can be expected. The plants induce new inflorescences in autumn and are overwintered in the glasshouse to produce a second harvest the following spring. Artificial lighting is used to extend the day length and break dormancy after a short winter period. This cyclic lighting is used at low light intensities and will increase truss elongation, increase yield, and improve fruit grading (Lieten, 1997; Van Delm et al., 2012). Harvest takes place from mid-April to early June and yields between 6–9 kg.m^–2.

An alternative to the double cropping systems is a fresh winter planting with trayplants after the autumn crop. At the moment, Clery and Sonata are the main cultivars, planted in mid-December and end of December–early January, respectively. Plant densities are higher, up to 14 plants.m^–2. The plants are in the cold store for at least 4 weeks (‘Clery’), and preferably longer for ‘Sonata’ due to the higher chilling requirement (Lieten, 2009). The production with ‘Clery’ starts in early March and continues until the end of April, with an average yield of 4.5–5.5 kg.m^–2. ‘Sonata’ is mainly harvested between 20 Mar. and the end of April, with a total yield of 5.5–6.5 kg.m⁻².

A summer crop can be planted between a spring and autumn crop, as well as with double-cropping systems (‘Elsanta’) as with the fresh winter plantings. Plantings are mainly in May and result in a harvest in July. Yield is between 2.5–3 kg.m^–2. In this way, three harvest periods a year can be done in the glasshouse.

Year-round production with assimilation light

In the more recent years, some growers started to use assimilation lighting in the glasshouse. Growers use high pressure sodium (HPS) lamps, but in trials at Research Centre Hoogstraten, LED lamps also proved to have possibilities.

The main aim was to advance the season from a December planting. In this way, ‘Clery’ could be harvested in mid-February instead of in March. Another progress made since 2013–14, is the use of ‘Sonata’ plants produced in the previous year for winter production in October. Together with assimilation light, this system makes production possible from the end of December until mid-February on a high-quality level. Assimilation light hereby completes year-round production of Belgian strawberries.

Current status and future prospectives

Over the last decade, total year production of Belgian strawberries is still increasing. From a total of 36,982 tons in 2003 towards a total of 47,786 tons in 2014 (Figure 3). The average price per year is quite stable between 2.5 to 3 euro per kilogram. Import as well as export increased tremendously over the past 35 years, but Belgium has always been a net exporting country (Table 1).

Table 1. Strawberry trade in Belgium: Import and export in volume and value.

	1980	1985	1990	1995	2000	2005	2010	2015
Import volume (tonnes)	5,340	6,880	9,768	11,497	24,305	38,658	26,465	29,188
Export volume (tonnes)	8,082	7,533	19,639	28,727	39,581	51,152	38,761	53,243
Import value (10^6 €)	9.08	13.61	17.20	14.36	32.98	54.02	62.84	74.79
Export value (10^6 €)	9.94	16.11	38.08	53.84	90.99	104.34	151.96	151.22

Source: VBT derived from NBB.

Figure 3. Evolution of strawberry production (kg) and prices (euro/kg) in Belgium. (Source: VBT Statistics.)

For many years, Belgian strawberries were available from the beginning of March until the beginning of January. The last few years, artificial lighting gave rise to year-round strawberry production in Belgium. About 70% of strawberry production occurs in May, June, July, and August (average of 2010–2014; see Figure 4).The average price is the highest in January (€7.20/kg) and decreases to the lowest prices (€2.40/kg) in summer months (Figure 4). While the early production and winter production under assimilation light are increasing, the summer production will remain the most important in the future.

Figure 4. Average month production (2010–2014) and average price/kg strawberries in Belgium. (Source: VBT Statistics.)

The cultivar Elsanta has dominated the strawberry market in Belgium since 1985. In 2014, 76% of the strawberry production was ‘Elsanta’ (Table 2). Since 2007, new cultivars, such as Sonata, Clery, and Portola, are grown at some strawberry growing enterprises but represent less than 10% of the total year production. ‘Sonata’ resulted in 3.6% and ‘Clery’ in 1.0% production in 2014. ‘Portola’ achieved 3.0% in 2013, and is estimated to have a similar production in 2014 (no data in 2014). Despite the small share, these other cultivars are an important development in the Elsanta-dominated strawberry production in Belgium.

Table 2. Strawberry production in Belgium: Volume of different cultivars in 2013 and 2014 (kg) and their percentage (%), destined for the fresh market.

Cultivar	Kg in 2013	% in 2013	Kg in 2014	% in 2014
Elsanta	34,806,908	75.63	36,666,520	76.73
Sonata	1,649,960	3.58	1,721,735	3.60
Portola	1,390,513	3.02	0^z	0.00^z
Clery	775,515	1.68	471,881	0.99
Darselect	426,272	0.93	171,016	0.36
Figaro	30,824	0.07	74,428	0.16
Other cultivars	6,944,813	15.09	8,679,360^z	18.16^z
Total	46,024,805	100	47,784,940	100

^zThe data for Portola in 2014 are included in ‘Other cultivars’. It is estimated that the volume of Portola in 2014 was similar with 2013.

Source: VBT Statistics.

Pest and disease management is also of great importance. The main diseases are powdery mildew (Podosphaera aphanis), grey mold (Botrytis cinerea), or diseases cause by soilborne pathogens (Phytophthora spp., Verticilium dahliae, etc.). The most common pests are spider mites (Tetranychus urticae), aphids, Western Flower Thrips (Frankliniella occidentalis), whiteflies (Trialeurodes vaporariorum), and more recently Spotted Wing Drosophila (Drosophila suzukii). Bacterial diseases, such as angular leaf spot (Xanthomonas fragariae) and more recently Erwinia pyrifoliae are present but are of less importance. Coming from chemical control of pests and diseases, more and more biocides and beneficials are used by growers, resulting in a more sustainable production. Despite this evolution of integrated pest and disease management to even more biological control, organic production of strawberries is negligible in Belgium.

Future developments will increase strawberry production in the winter months (November until March), where assimilation light will allow production in this time of the year in Belgium. Next to that, it is also likely that in the future the surface of table-top systems will change to more soilless production. Finally, the short day cultivars are preferred up until now, because of programmed harvest periods, among others. The yield and timing has been predicted by flower bud analysis over the past years (Van Delm et al., 2014), and the number of analyses for growers are still increasing. Since everbearers are gaining interest, this will become the new frontier for programmed strawberry production (Neri et al., 2012), but cultivation techniques are improving to obtain more predictable cropping; thus, it is expected that everbearers will claim their spot in the future Belgian strawberry culture.