Title: Protected Strawberry Production

CALU TECHNICAL NOTES
Topic: Horticulture
Ref: 020203
Title: Protected Strawberry Production
Date: April 2007
INTRODUCTION
World strawberry production is focused in the Northern hemisphere and in the UK they remain the major soft
fruit crop in production. At the peak of harvesting in June/July, UK grown strawberries meet 80 – 85% of total
demand, any shortfall being made up from imported fruit. Currently 80% of UK strawberry production for
supermarkets is grown under polythene tunnels - although this may decrease in the future due to changes in
planning regulations. Through the use of improved varieties and production techniques, and by growing crops
under polythene tunnels, the strawberry harvest in the UK can be extended to 26 weeks. Fruit yield and
quality are affected by several interacting factors, important environmental factors include: temperature; day
length; winter hardiness; disease resistance; tolerance of soil conditions and high temperature resistance.

The advantages to the grower of using tunnels are:
the extension of the fruit season to approximately 26 weeks (May to mid Autumn);
improvement in class 1 grade fruit and reduced wastage. Class 1 grade (supermarket saleable fruit)
for outdoor production is generally 50-70% while under protection it is nearer to 80-90%;
as the fruit is produced in controlled conditions there can be reduced use of pesticides by up to 50%
against Botrytis, downy mildew and black spot;
provision of an improved environment for the use of biological control;
increased opportunities for organic production due to the reduced incidence of disease and the
enhanced use of predators;
guaranteed conditions to carry out production and harvesting operations and no need to stop the
pickers in poor conditions or to have long waits for early dew to burn off.

TUNNEL TYPES
The two main types used are French and Spanish tunnels. Spanish types have wider bay spans, ridge heights
of 4 metres and are all connected rather than being separate, this improves ventilation and materials handling.
The plastic in Spanish tunnels stops 1metre from the skirt line also improving ventilation. French tunnels are
not as high, tend to be individual structures and the plastic is extended to ground level.
Haygrove tunnels (www.haygrove.co.uk) are available in different configurations from single bays 8.5m wide
through multi-spans to telescopic designs that wil alter the air volumes according to the time of year and
growing style required.
The tunnels are not permanent structures so they can be moved to cover crops as required. The covers can
be used to force an early crop or to cover the crop as it becomes ready for picking.
Codes of practice for the use of polytunnels for the production of soft fruit are available at:
www.tunnelfacts.co.uk/code
www.britishsummerfruits.co.uk/polytunnels
www.cpre.org.uk/filegrab/polytunnels-policy
VARIETIES
Strawberry varieties are grouped according to their harvesting periods. Table 1 shows the most widely
available varieties. Certified plants should be selected which provide a guarantee of trueness to type and
freedom from specific pest and diseases.
The varieties currently available were developed for outdoor production and are not always suitable for
growing under tunnels. The main variety used is Elsanta which accounts for about 65% of total production.
Reliance on one variety can lead to over production in the second and third week of June and a tendency to
produce too much leaf for intensive production under protection. Florence is an important July cropper and its
disease resistance makes it important for organic production. However, it does have a tendency to bruise if
harvested in hot weather, which makes it less acceptable to the supermarkets. Further research by DEFRA
wil determine whether or not new selections of Florence with improved firmness and colour have lost any of its
beneficial characteristics.
Visit www.calu.bangor.ac.uk for more leaflets. For further information please contact CALU – e-mail: calu@bangor.ac.uk tel: 01248 680450.
Whilst every ef ort is made to ensure the information provided in this leaflet is correct, CALU cannot be held responsible for the consequences of any actions taken on
the basis of its content.

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CALU Technical Notes: 020203 – Protected Strawberry Production
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More work is to be carried out to develop more compact plants with improved fruit to leaf ratios, increased yield
per hectare, high grade 1 production and reduced wastage.

Table 1: Strawberry varieties and characteristics
Type
Harvest Period
Fruit Size
Crop
Disease resistance
Early and mid summer Varieties



Elvira June/early
July
Meduim
Heavy
Honeoye

Medium
Heavy
Susceptible to mildew
when under stress
Pantagruella
Medium/Large
Low

Mid summer varieties



Pegasus
July
Large
Heavy
Resistance to wilt, rown rot
and mildew
Elsanta
July
Large
Heavy
Generally susceptible to
disease
Hapil

Very Large
Heavy
Susceptible to mildew and
verticillium wilt
Cambridge Favorite July
Medium
Medium Heavy
Susceptible to botrytis in
wet conditions
Alice

Large
Medium
Resistance to wilt, crown
rot and mildew
Late Summer

Symphony
Late July early
Large
Heavy
Good disease resistance.
August
Grows well in damper
conditions.
Florence
Late July early
Large
Heavy
Good disease resistance
August
especially mildew. Some
resistance to vine weevil.
Sophie
Late July early
Large, good
Heavy
August
quality
Rhapsody
Late July early
Medium Medium
August
PLANTING
Strawberries can be planted on the flat or in raised beds, often through coloured plastic mulch with trickle
irrigation system laid under the mulch. Raised beds improve drainage and increase the rooting zone available
to the developing plants. If the height of the raised bed is 40cm, pickers are more likely to stay standing rather
than pick kneeling, this improves harvesting output. For crops established through coloured plastic mulch,
runners produced by mother plants are removed and the resulting crowns are the primary source of fruit.
Certified runners should be planted into moist well-prepared soil in July, August and September. In late
established plantations, runners are deflowered to encourage further crown development and increase yield
for the next season.
SPACING
Runners should be planted with the crown of the plant just level with the soil surface. Runners should be
planted approximately 45cm apart down the row with 100cm between rows. On lighter soils runners are
planted at 40cm centres within the row with 75cm between rows.
Bare root, over-wintered cold-stored plants (-1.5oC) can be planted in early spring with fruit ready for picking
60 days later. The crop can be protected as it gets close to harvesting.
Visit www.calu.bangor.ac.uk for more leaflets. For further information please contact CALU – e-mail: calu@bangor.ac.uk tel: 01248 680450.
Whilst every ef ort is made to ensure the information provided in this leaflet is correct, CALU cannot be held responsible for the consequences of any actions taken on
the basis of its content.

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CALU Technical Notes: 020203 – Protected Strawberry Production
3 of 3
WATERING / IRRIGATION
Strawberry plants should be watered regularly in the first few weeks after planting to encourage root
development. Watering may need to be continued under dry conditions. Once fruit set has occurred excess
use of water may encourage the development of grey mould (Botrytis cineria) which results in fruit rotting. This
is a particular problem where crops are irrigated overhead. If irrigated by trickle systems the leaves and fruit
remain dry and infection is drastically reduced.
MULCHING
Unless plants are established through polythene, crops should be strawed down to ensure the developing
fruits are prevented from coming into contact with the soil. It is advisable to apply slug pellets along the rows
and then apply straw ensuring it is pushed into the plant canopy to provide a barrier between the soil and fruit.
Keeping the inter row areas mulched with straw wil further suffocate weeds and retain moisture for up to six
weeks.
WEED CONTROL
Weeds can hamper harvesting and cause uneven ripening. Land should, where possible be free from
perennial weeds either by use of herbicide or by cultivation to dry out roots or the use of stale seedbed
techniques. Polyethylene sheeting can be laid up to 4 weeks before planting to encourage weed seedlings to
emerge and die under the covering. The use of woven polypropylene sheets can be more expensive but they
wil last longer saving labour and disposal costs.
HARVESTING
The optimum time to harvest strawberries is the early morning when the fruits are cool. If picked later in the
day, the berries wil need to be cooled to remove the field heat and maintain their quality. Fruit should be
uniformly coloured and be harvested complete with a stalk conjoined with the berry.
POST HARVEST MANAGEMENT
Peg down runners to retain matted rows unless grown through plastic or polypropylene mulch in which case,
remove unwanted runners. Reduce foliage volume by topping the leaf canopy. Controlled burning of straw
mulch wil assist in reducing the likely build up of pest and diseases.
PESTS and DISEASES
A range of insect pests can affect strawberries. For example, vine weevil infestation of the roots can result in
plant collapse particularly in the spring when rapid growth occurs. The leaves and crowns can be infested with
aphids, which cause leaf curling and distortion. Slugs can attack fruit producing holes and rendering the fruit
un-saleable. Strawberry seed beetle can eat the seeds from the surface of the berry disfiguring the fruit. For
both pests and diseases on strawberries cultural controls can significantly reduce the severity of attack.
Varieties differ in their susceptibility to fungal disease attack. Root and crown rot caused by Phytophthora
species is most common in heavier soils. Infected plants collapse due to the fungus attacking the roots and
vascular tissues in the crowns. Mildew primarily attacks the leaves of susceptible varieties, however in these
crops infection can spread to the fruit. The most common fungal disease attacking the developing fruit is
Botrytis cineria – grey mould. Routine fungicide spray during the flowering period wil reduce the incidence of
this disease.

Associated CALU Technical Notes:
020202 Field strawberry production

Visit www.calu.bangor.ac.uk for more leaflets. For further information please contact CALU – e-mail: calu@bangor.ac.uk tel: 01248 680450.
Whilst every ef ort is made to ensure the information provided in this leaflet is correct, CALU cannot be held responsible for the consequences of any actions taken on
the basis of its content.

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