Table of Contents
- Introduction About Strawberry plant
- Strawberry Propagation
- Production Systems for Strawberry
- Plant Density, Pruning, Pollination, and Fruit Growth of Strawberry
- Production Environment for Strawberry
- Strawberry Crop Nutrition
- Strawberry Pests, Diseases and Disorders
Introduction About Strawberry plant
Hydroponically cultivated strawberry plants yield and produce well, and in many climates, the protected, heated environment of a greenhouse enables year-round or out-of-season production. Strawberry producers use greenhouse structures to either extend the cropping season or produce out of season fruit when returns are highest, or to avoid some of the production issues that soil-based systems face.
Strawberries are a crop that may be produced as an annual or a long-term crop, making them ideal for hydroponic production. Strawberries are a small but extremely productive plant Many growers prefer annual cropping systems because they generate their best yields of high-quality fruit in the first season. Crops are normally grown for 5 to 10 months before being replaced.
Commercially there are two main groups of strawberry plants:
- Day Neutral Plants
- Short Day Plants
Day-neutral plants are induced to flower and fruit when temperatures are high enough to maintain growth irrespective of day length. With short-day varieties, floral initiation is triggered by short day lengths (less than 12 h) or by cool conditions. Refrigeration can be given to planting stock to provide the chilling period required for flowering.
strawberries are not raised from seed but vegetatively propagated from ‘runners’ which form on mature plants towards the end of the growing season. Runners from field-grown crops are harvested in autumn or winter and stored bare rooted before being used to establish new crops. These field-grown runners, once washed and given a fungicide application, can be used as planting stock for hydroponic crops; however, there is still a risk of the carryover of crown and root rot diseases using this method.
A preferable type of planting material is tip cuttings of strawberry runners which have been raised as plugs in soilless growing medium, thus have not been in contact with soil. Runner plants or runner tip cuttings used for strawberry crop establishment can be stored under refrigeration for an extended period of time, this process also providing the chilling period which is required for floral initiation.
Commercial growers prefer to use larger grade plug cell transplanting as planting stock as this ensures the crown has fully developed a new root system before transferring to the hydroponic system and has a good store of assimilate for new growth and early fruit development.
Production Systems For Strawberry
Hydroponic strawberries are grown in a diverse range of soilless systems, including solution culture methods such as NFT; however, substrate culture dominates commercial production as this allows support of the plant grown at the correct depth and control over root-zone moisture levels.
Strawberry plants are prone to infection by root and crown rot pathogens, particularly in the early establishment phase, and thus control over irrigation is vital for success of this crop. Commonly utilized substrates include rockwool (both slabs and granulated), coco fibre, peat, perlite, pumice, bark, LECA, untreated sawdust, rice hull and organic mixes.
For the production for strawberries systems include standard single-plane cropping, hanging gutters, vertical or ‘stacked’ pots, columns or staggered systems. Systems for growing strawberries that are vertical, hanging, in columns, or in stacked pots are designed to maximize greenhouse space by increasing the plant density in comparison to single-plane cropping.
In this type of system has more plants and larger production potentials, plants on the lower levels are heavily shaded, making it best suited for cropping in high-light areas or in situations where supplemental lighting is possible. Single-level or staggered-level troughs are composed of one or more levels of troughs filled with substrate, supporting slabs, or growing medium like Rockwool or coconut fiber, allowing for optimal light absorption by all plants.
They allow for air movement up and under the canopy to help prevent disease and are positioned at a comfortable height for plant maintenance and harvesting.
The rows of troughs are drip irrigated with the nutrient solution, and each one has a collection channel that allows it to drain. Plants are established into the tops or sides of troughs and after developing sufficient foliage, fruit trusses are trained over the edge of each trough so that they are held clear of the foliage and growing substrate.
Plant Density, Pruning, Pollination, and Fruit Growth of Strawberry
Plant density depends up on with the type of production system used and environmental conditions. Low light levels can negatively impact yields and berry quality, while high light levels can stress plants and interfere with their ability to grow. In single-level or staggered trough-type systems, densities of 12 – 24 plants/m2 are typical; this is rather cultivar dependent.
For strawberry plants require little pruning; however, removal of the lower, older leaves as they age and senesce assists with good rates of air flow around the base of the plant for humidity removal and prevention of fruit and crop rot diseases.
The floral development is often on strawberry plants which have insufficient leaf area to support fruit growth and the first few flowers are removed until the canopy is of sufficient size. Once flowers are fully open, greenhouse strawberry crops needs pollination assistance for large, high-quality berry production.
Pollen formed on the stamens of strawberry flowers is dropped onto the receptacle during flowering, but insects, the wind, and plant movement also help to speed up the process. Large air blowers that move down the rows and direct a blast of air over the blossoms in strawberry plants in a greenhouse help with pollination.
Commercial farmers can also employ portable beehives to pollinate greenhouse plants. On a smaller scale, brushing over the tops of the plants will also facilitate pollination. Pollination must be carried out daily as high rates of pollen transfer are required. Insufficient or uneven pollination will result in misshapen and undersized fruit.
Production Environment for Strawberry
Strawberries have a reasonably high light requirement for good yields and high quality fruit. According to Miyazawa et al. (2009) during the vegetative stage, optimum DLI was 29.3 mol/m2 per day for strawberry growth at a temperature of 25°C.
For the greenhouse strawberry production temperature range of 16–25°C are suitable. Slow the emergence of new leaves and extend the fruit development phase, due to low temperature.
High temperatures above 30°C both in the root zone and aerial environment tend to inhibit strawberry growth and fruit
Fruit quality also suffers with a loss in flavour and an increase in softness combined with rapid ripening under warmer conditions. It is possible to manipulate plant growth and fruit development by chilling the root zone to 10°C (Sakamoto et al., 2016) under warm and tropical growing conditions.
Strawberry crops respond to the use of CO2 enrichment which gives increases in yields and lessens the time to harvest. Enrichment to levels of 700–900 ppm CO2 has been found to give an increase in total plant yield of 50–70% (Itani et al., 1999).
Strawberry Crop Nutrition
To maintain good fruit quality for the strawberries requires high levels of potassium during the fruiting phase. During the establishment and early vegetative stage a formulation which provides an N:K ratio of 1:1 may be applied until the time of fruit set on the first inflorescence, with the level of potassium gradually increased as fruit load increases on the crop.
According to Morgan, 2006 N:K ratios for strawberries typically fall within the range 1.0:1.7 to 1.0:2.0 during the fruiting phase.
Under low temperature conditions plants are prone to iron deficiency due to reduced levels of iron uptake. Depends up on the environmental conditions, stage of growth and system of production EC levels for strawberry production vary. Minimum EC of 1.6 mS/cm is required during the harvest period to maintain good fruit quality from all systems.
In Winter Low-light conditions, EC levels are run higher at 2.2–3.0 mS/cm to maintain fruit quality with lower levels run in summer and under higher-light conditions to prevent excessive plant stress and assist with water and calcium uptake.
Strawberry Pests, Diseases and Disorders
Common pests include greenhouse whitefly (T. vaporariorum), tobacco whitefly (B. tabaci), greenhouse thrips (H. haemorrhoidalis), two-spotted mite (T. urticae), aphids and caterpillar larvae.
Under warm, dry growing conditions, mites can be a particularly damaging and difficult-to-control pest on strawberries with early control required because crops can be destroyed by this persistent pest. Outdoor hydroponic systems require bird netting for protection.
Diseases of strawberries are often connected to poor environmental control, particularly overirrigation of the root zone, predisposing the plants to root and crown rot pathogens and high air humidity which is a risk factor for foliar diseases. Wherever possible, cultivars with some resistance to common root rot pathogens like red stele root rot or red core (Phytophthora fragariae) should be chosen.
Other root rot pathogens include Pythium, Rhizoctonia, Fusarium and Verticillium which may spread through a crop from the initial source of infection
Fruit rots are common where fruit is in contact with damp substrates or when air flow is restricted and humidity levels high. Botrytis (grey mould) of fruit can occur under greenhouse conditions, particularly under cooler temperatures, and leather rot (Phytophthora cactorum) may also infect ripening fruit.
Malformed berries are commonly caused by poor pollination or damage to the achenes (small seed-like structures) on the surface of the fruit. Temperatures which are too high or too low also contribute to malformed fruit and undersized berries.
Overly soft fruit texture is often a problem where crops have been grown under temperatures that are higher than optimal but can also be due to incorrect plant nutrition and low EC levels.
Deficiencies in potassium during fruiting is another common cause of soft fruit which does not store well, as is low levels of calcium or restrictions in calcium uptake by the plant.
Strawberries require daily harvesting as they must be removed from the plant at the correct stage of maturity when at least
three-quarters ripe rather than when over-mature and starting to soften, which reduces shelf-life.
Allowing fruit to fully ripen on the plant results in a greater flavour and sugar levels than those harvested at the first signs of coloration. Fruit harvesting should occur in the morning when temperatures are still cool and the plants turgid.
Once harvested berries require cooling to below 5°C as rapidly as possible to prolong shelf-life and fruit quality.
- A Practical Gide ” Hydroponics and Protected Cultivation By Lynette Morgan
- Leafroller caterpillar on a green leaf. Photo credit: Shutterstock/Garmasheva Natalia
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