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From the farm to the cup: A-Z of growing big strawberries

Saturday March 11 2017

Picked strawberry fruits.

Picked strawberry fruits. Always keep the picked strawberries out of sunlight, wind and dust. FILE | NATION MEDIA GROUP 

PROF JOE WOLUKAU
By PROF JOE WOLUKAU
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Angela, June bearing, Day neutral, Ever bearing and Seascape are not varieties of strawberries, but categories, just like tribes for people.

Within the broader groups, however, we have varieties. There are over 40 varieties of strawberries, but three namely Chandler, Pajaro and Selva are very popular in the country.

The three fall in the hybrid category and are mainly grown for export. Below are the varieties:

Pajaro: It is a fast-growing variety, popular for large berries and good flavour.

Chandler: This is a high-yielding plant that produces large and firm fruits within 60–75 days. The fruits are not only large but have good flavour and firm skin.

Selva: A neutral day variety producing small berries with good flavour and colour.

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Fern: A neutral day variety with heavy yield of large fruits but lighter than all the others.

Aiko: Uniform, large, long fruit of conical shape, with a pointed end, firm flesh, pale red colour, slightly sweet, very resistant to transport and high yield.

Douglas: Matures early, has clear foliage and offers good fruits of elongate conical shape and orange-red colour. It has firm flesh, which is red-coloured with a pink centre, and a good taste.

The crop is high-yielding. Other varieties include Nanandreas, Albion, Red glory, Manhattan.

Source and cost of planting materials

The cost of planting materials (seedlings) average Sh15 per split/seedling upward. Kalro Njoro/Thika, Horticulture directorate or Department of Crops, Horticulture and Soils (Egerton University) have quality planting materials.

How to produce sweet, large fruits

Site selection

If you want to get nice big, well coloured fruits from your back garden, the best place to plant them is in the sunniest part.

Strawberries grow better in a garden site that is open to direct sunlight most of the day.

You should try to avoid very low-lying areas that are prone to frosts. Avoid planting where tomatoes, eggplant, potatoes, peppers, raspberries or black berries have been grown in the last three years.

These plants can act as hosts for fungi and insect pests that build-up in the soil unless you place them on at least a three-year rotation schedule.

Strawberry plantings can remain productive for three to four fruiting years.

It is possible to minimise the onset of disease and insect problems through rotation of the strawberry patch from one site to another, every time you carry out a new planting.

Choice of variety/cultivar

It is prudent to select only varieties adapted to the climatic conditions (day, neutral or June bearing strawberries) of the part of the country where you live.

For the Kenyan conditions, Chandler, Douglas, Aiko, Pajaro and Fern will do well.

Propagation

Strawberries are normally propagated from split or runner plants, which are rooted. Splits or runners should be selected from vigorous, high-yielding and disease-free plants.

The crowns may be divided to get new plants but this is somewhat more difficult.

Make sure you get disease-free plants from a reputable nursery since it is not a good idea to utilise your own plants or neighbour’s.

Horticultural Crops Directorate and your extension agent would be able to give you advice on suitable sources of planting material.

TRANSPLANTING

Transplanting time will vary from region to region.

Before planting the strawberries, soak the root for about an hour or two but not longer, and then plant them right away. A cool cloudy day is the best to plant.

The plant should be placed with the crown at the soil surface or the roots may dry or the plant may rot.

The hole should be deep enough so that the roots can be placed straight down into the hole.

Remove any damaged roots before planting.

Place the plant at the proper level into the hole and fill it with the soil.

Put the soil down firmly and keep the plant well-watered for two weeks after planting.

Planting density and depth
Spacing and row filling have effect on fruit yield: The common practice is 30cm between plants and 60cm between rows (90 cm for the vigorous cultivars).

Planting is done such that the mid-crown is at the soil line. Deeper planting encourages root rots and leaves take longer to emerge.

Transplanting can be done by hand or by a planter.

Raised bed
Planting on raised beds promotes good water drainage and larger berries are also encouraged to develop.

Beds should be 60 – 75cm wide, 100 – 120cm apart with plants 15–30cm apart over the beds.

Runners are placed over the beds until wide rows are developed.

Planting strawberries in containers

Growing strawberries in containers or pots is easy to do, even if you don’t have much outdoor space. You can grow strawberries in containers on your balcony or any sunny outdoor area.

In fact, pots, cans and other containers are a great way to grow strawberries. Just feed and water your container-growing strawberry plants regularly and enjoy strawberries throughout the year.

Irrigation

Irrigation is critical immediately after planting for crop survival. As the plants are shallow rooted, they require 2.5cm of water per week for 12 weeks per growing season.

Irrigation increases yields by 2.5 times (250 per cent), boosts runner rooting, growth rate, flower bud formation, useful in pesticide application, frost control, prolongs harvest and cools the crop to prevent sunscald.

For this purpose, sprinkle at noon so that water is not moved from fruit into leaves for transpiration.

Fertilisation

The strawberry plant is shallow-rooted and requires fertilisation during the growing season to keep it vigorous.

It is best to first get your soil tested to determine what nutrients are available, information relating to soil pH and other important soil characteristics. Avoid planting with fertilisers to avoid dehydration of the splits, since the plant goes into dormancy for 14 days.

Nitrogen
Nitrogen is the most important and is critical in subsequent growth.

There can be response to nitrogen fertiliser on poor soils or soils low in nitrogen though an excess of the mineral will result in excessive vegetative growth with little or no fruit production.

After 30 days, fix CAN 10g per hole in between the plants. The second month, top dress with NPK 17:17:17, 10g (a tablespoon) per hole between the plants.

Fertilisers should be used to maintain soil fertility and maximise plant growth and fruit production.

Strawberry is considered a heavy feeder so regular boosting with foliar feeds like Easygrow® improves vegetative, flower and fruit growth and provides calcium to firm the skin of the fruit and to decrease fruit deformities.

Flower and fruit management in year one (De-blossoming)

During the first season, the flowers and runners should be pinched off to enable better future crops of berries. Though the one in seven rule may be used to allow for fruit production the first year.

Kenneth Kinuthia and his wife Beth Wairimu in
Kenneth Kinuthia and his wife Beth Wairimu in their two-acre strawberry farm in Nyandarua. For the Kenyan conditions, strawbeey varieties such as Chandler, Douglas, Aiko, Pajaro and Fern do well. PHOTO | JOHN GITHINJI | NATION MEDIA GROUP

This allows one out of every seven flowers on the plant to produce a berry with the rest being pinched off for better berry production while having little effect on root development.

Weed control
It is essential for good production.

The weeds can effectively compete for water and nutrients with the shallow rooted strawberries. They should be hand pulled but care must be taken into not damaging the shallow roots of the strawberry plant.

Some hand hoeing and weeding is necessary to keep weeds out of the inter-rows.

During weeding, train the runners away from inter-rows by placing in better positions.

Several weedings are necessary.

Some herbicides are useful in floor management in strawberry, reducing the amount of hand labour and number of cultivations and protect soil.

However, if the initial field preparation in year of establishment was done well, later problems of weeds especially perennial grasses is minimised.

Common herbicides include treflan, tenoran, sinbar, lantrel. Geese haven been used in North America to control grass weeds like foxtail and crabgrass.

Mulching

Mulching in strawberry will improve plant survival from strong cold/hot dry winds, reduces low temperature injury (insulative), conserve moisture/constant soil moisture, reduces irrigation, smothers out weeds, eliminates hand weeding except in planting slots, keeps berries clean and aisles accessible, reduces soil rot, adds organic matter to the soil and helps in vigorous plant growth.

Problems with mulching, however, include high cost of material and labour, it leads to rise in volunteer weeds for straw mulches, slugs and rodents increase and there is extra heating if put on too thick during dry conditions.

For organic mulch, spread 5-8cm thick. You can also use plastic mulches.

PEST MANAGEMENT

Aphids (Capitophorus fragariae): They are very troublesome pests for strawberry as they feed on the sap of the plants causing loss in vigour and transmit viral diseases.

They are managed quite easily by sprays of malathion and dimethoate.

Nematodes: Severe in sandy soils than in clay with a high organic matter content. Several types exists like the lesion nematodes (Pratylenchus spp), which attacks roots causing amber to dark-brown spots.

In severe cases, the roots rot.

Then there is bud nematode (Aphelenchoides spp) that causes what is called red plant as it lives and feeds among the developing leaves.

Root-knot nematode (Meloidogyne spp), on the other hand, penetrates and feeds small roots causing knots.

Severe infestations cause stunting, wilting and death of the plants. Plants also develop few runners and low fruit yield is observed.

Use nematode-free plants, practice crop rotation and soil fumigation to curb the pest.

Tarnished plant bug or lygus bug:The adult is coppery brown with piercing and sucking mouth parts.

The bugs feed on achenes. The stink bug may also damage the berries causing uneven ripening.

Sprays with diazinon, malathion or dimethoate.

Mites: Red spider mite (Tarsonemus fragariae) feed on the young and tender leaves especially on the underside.

Mites can be a nuisance in dry weather. Irrigation can, therefore, be a control measure. Affected plants are stunted and yield poorly.

Spray with Kelthane and other appropriate pesticides (acaricides) is advised in dry seasons.

DISEASES
Powdery Mildew (Sphaerotheca humcili): Attacks the foliage which show an upward curling of the leaf edges and cobweb like mould on the lower surface.

In severe cases, the fruits may also be affected, in which case maturation will be interfered with.

Botryitis or grey mould (Botryitis cinerea): Starts as a blossom infection and spreads to the fruits both in the orchard and in the store.

The fruit is normally covered with a light–grey mould made up of fungal spores and mycelia. Sulfur or copper dusts are effective.

Root rots: Several forms of root rot are known to be caused by fungi. The commonest root rot is the one caused by Pphytophthora fragariae.

The rot is characterised by a red core, dwarfing, failure to grow and eventual death of the plants is common. Thorough site preparation is the best option for managing root rots.

Viruses: Produces mottling, yellow-edge, crinkle chlorosis, leaf curls or dwarfing. Viruses can either be (a) killer or (b) latent.

They produce severe symptoms and kill the individual mother plants and attached runners. The latent type is responsible for progressive weakening of the plant by reducing number of runners, low fruit yield and small dull berries.

Viruses can be managed by destroying all affected plants, control aphids.

HARVESTING
Fruit harvested in the morning will usually have a longer shelf-life.

Pick the berries when the top of the strawberry is completely red, once picked they will not continue to ripen. Make sure you pick all ripe berries.

A fruit left on the plant overripes, which helps promote development of disease and causes insect problems.

You can refrigerate strawberries for several days. You should avoid washing fruit until just before you use it, this is necessary to avoid softening and decay.

Home-produced fruit brings its own rewards even aside from the obvious satisfaction of eating from your very own crop. It’s a pleasant hobby for young and old alike.

Renovation
Mow tops at end of harvest season to rejuvenate growth. New leaves are more vigorous in photosynthesising than old ones.

New branches (branch crowns) and new fruit buds form better. Old leaves produce inhibitors of flower bud initiation while stripped leaves are collected and burnt to reduce disease pathogen inoculum load.

Post-harvest technology

Strawberries have a short fresh period and, therefore, the cold chain is very critical during the post-harvest period of the berries.

Keep the picked berries out of sun, wind and dust. The useful post-harvest life of strawberry depends on the cultivar, degree of ripeness, handling and care, temperature when picked and kept.

For every rise of 80C, the life of berries reduces by 50 per cent, berries picked early in the morning and pre-cooled stay longer, look fresher than those picked at midday then left in the sun.

Berries pre-cooled to 40C within two hours of harvesting and kept at this temperature look better in the market.

Strawberries have a short (2-3 days at 120C) storage period. Best temperature, however, is 40C for 4 days at 85-90 per cent relative humidity.

Grading is essential for fresh market and for fetching good prices. Standards are available for specific markets especially the European community.

Marketing

They include food processing firms for jams, flavours or juices, supermarkets, hotels, households and selling in export markets.
Consumption

Fruits are eaten fresh, as syrups, juices or concentrates. Flavours are extensively used in the food industry from strawberry cakes, ice creams, milk shakes, jams, yoghurts and wines. The fruit is rich in vitamin C.

Prof Wolukau is a Senior Lecturer at the Department of Crops, Horticulture and Soils, Egerton University.