Strawberries have been cultivated for many years, in the past by the Romans as far back as 234 BC. In those days they were believed to have been an aphrodisiac. When the colonists arrived in America the native Indian Americans were already eating strawberries. It is believed that in 1780 the first hybrid was developed in the United States of America and the first strawberry introduced into South Africa in 1656.
Strawberry production, both for fruit and young plants, can be a very profitable enterprise as a sideline to existing crops or as an entity in its own right. The crop can be grown over a wide range of climatic and soil conditions, although performance is best at altitudes above 900 metres. As the strawberry is an herbaceous plant the cultivation techniques are different from those required for bush and tree fruits. The fruit, which is the edible part, is really a false fruit. Technically the strawberry is a swollen fleshy receptacle embedded with small dry one‐seeded fruits called achenes. The fruit is rich in Vitamin C and contains as much as oranges and lemons. The modern large‐ flowered and fruited strawberries originated from American species. They have a higher chromosome number and have produced fertile hybrids which have led to our modern varieties.
The following are varieties which do well:
This is a relatively new cultivar released in South Africa in 1973. It starts to bear early in winter in frost‐free areas and produces large fruits which, in Winter, tend to be ‘Wedge’ shaped. Berries are firm, large fruits and yields are good with vigorous plants producing many runners.
An American cultivar which produces large, tasty, firm fruit of good colour. Berries ripen uniformly even during winter. In summer, the berries are sour although not as sour as some varieties. Plants are vigorous and produce good runners. The Western Cape achieves the highest yields.
CLIMATE AND SOIL
A deep sandy loam soil is preferable. This type of soil has several advantages which include good moisture and nutrient‐holding characteristics together with a good response to manuring and few drainage problems.
Good yields however, can be obtained if fertilisation and irrigation are maintained at adequate levels. Soils with high clay content should be avoided. Preparation of the land well in advance of the planting date is desirable.
Once the crop has been planted there is little chance of performing any further cultural operations. Attention must be paid to the soil level, structure, fertility and drainage as well as weed and eelworm control measures. Ideally, soil pH should be between 5.5 ‐ 6.5 (Ca Cl2) for best results since nutritional problems may arise on more acid soils. If manure is not obtainable a suitable green crop can be grown and ploughed in well in advance of planting, to ensure that the green crop has
adequate time to decompose. The potential income per unit is very high so the use of fertilizer is well justified. A 1 in 4 year cycle is recommended. Strawberries prefer a climate that has very cold winters and moderate summers.
PLANTING DATES AND SPACINGS
Strawberries are usually planted from February onwards as new runners become available. May is usually the latest planting date after which yields become very low as the root systems cannot develop sufficiently before winter commences and they are sensitive to day length. Generally the earlier the planting the better the yield. On small operations, where large implements are not necessarily available, only sufficient space need be left between beds for access when picking the fruit. Beds of 4 – 6 rows can be used, with spacing of 300 mm x 300 mm between rows in the bed with 600 mm between beds. Strawberries can be planted in single or double rows, giving populations of between 55 000 single and 74 000 double row plants per hectare.
Fertilizer use is well justified as organic matter alone is not sufficient. Strawberries respond well to potassium, 150 – 200 kg/ha of potassium sulphate should be applied depending on the soil type. Single superphosphate should be applied at the rate of 500 – 700 kg/ha, depending on soil analysis. Fertilizers should be incorporated into the seedbed to a depth of 200 – 300 mm shortly before planting.
As soon as the plants become established, which is usually within a month of planting, a top dressing of 75 – 100 kg/ha of ammonium nitrate is recommended with a further application of the same quantity a month later. When the resurgence of growth commences in the spring, a mixture or 100 kg of potassium sulphate and 75 – 100 kg of ammonium nitrate may be applied per hectare and thereafter at monthly intervals. A final application of ammonium nitrate is recommended at the end of the cropping season at the rate of 75 ‐ 100 kg/ha which will promote better summer production.
5. PESTS AND DISEASES
The main pests are red‐spider mite and aphids which feed on the foliage, flowers and new shoots. Their feeding causes distortion of these parts. Early control is very important before populations increase to the extent where almost permanent damage has been caused. These can be controlled with a dose of Abamectin, Milbemectin and Dimethoate.
Another pest which may prove troublesome is the strawberry beetle, an iridescent green or purple insect. Both adult and larva feed on foliage and the fruit.
Root‐knot nematode is found in strawberry plants and can cause root damage leading to loss of yield. Guaranteed nematode free plants should be used in new lands and infested soil treated with chemicals such as Dazomet, 1.3‐Dichloropropene + chloropicrin and Methyl Bromide on an overall basis.
These can be a problem and are effectively controlled with Mesurol (Methiocarb) bait at the rate of 5 g/10 m2.
White grubs may also be a problem, but there is no effective control as yet.
Two viral diseases of importance occur and in time reduce production to sub‐economic levels. There is no control other than to plant annually virus‐free stocks.
Leaf diseases (leaf spot and leaf blight)
These infections generally occur late in the season and so are of no economic importance. Infection can, however, decrease mother plant vigour when used for runner production. Copper Oxychloride (200 g/100 litres water) applied every 14 days; or Captab (100 g/100 litres water) applied every 7 days up to 5% flowering.
Three important fruit rots occur, Botrytis, Rhizoctonia and Rhizopus. Losses can be severe but may be reduced by the use of suitable chemical sprays applied weekly during flowering. Good sanitation is necessary, aeration through the plants must be adequate, and mulches are recommended to keep the fruit off the soil. A chemical that can be used is Captab (100 g/100 litres water) or Fluopyram (500 ml/ha in 300 – 1000 litres/ha).
6. WEED CONTROL
Weeds can be controlled mechanically or chemically. Hand hoeing can damage the plant roots and fruit, as they grow closely together. It is also labour intensive and time consuming. Weed control is important as the weeds use up a lot of nutrients and water that should be used by the strawberries. Care must be taken when spraying herbicides as they should not come into contact with the plants. The instruction manuals on the chemicals must be adhered to, to avoid any unnecessary loss. Chemicals that can be used are Glyphosate (post‐emergence) at a rate of 1 – 6 litres/ha depending on the type and stage of growth of the weeds. It should be mixed into 50 – 200 litres of water/ha. Care should be taken not to get any of the chemical onto the plants as it will kill them. It is a non‐ selective herbicide. Another herbicide that can be used is Chlorthal‐dimethyl (pre‐emergence) at a rate of 8 – 12 kg/ha depending on the clay content of the soil.
Fruit for the fresh market should be picked as evenly coloured as possible. During the cooler months some cultivars tend to be white around the shoulder. Misshapen fruits result from inadequate pollination. Early morning picking and the exercise of the utmost care is recommended. Berries should be placed in single‐layer trays and never be exposed to the sun for any length of time.
The sooner the fruit can be removed from the heat of the field the longer the berries can be stored.
Storage temperature should be kept at or below freezing point.
For fresh market sales strawberries are packed and sold in punnets.
Yield: About 7 ton/ha. With the new breeds produced, yields up to 20 – 30 tons/ha