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STRAWBERRY (FRAGARIA SPP)
Strawberry belongs to the family Rosaceae. In Kenya the strawberry species most popularly grown is Fragaria vesca variety Ananassa. The strawberry plant is a low perennial growing above the ground with a short crown, leaves, flower trusses and runners (stolons) with runner plants. Roots arise from the short underground part of the stem (rhizome).
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Strawberry plants
Ecological requirements
Altitude
Production takes place in tropical highlands above 1000m a.s.l
Rainfall
Strawberry requires well distributed rainfall of about 1200mm. Where rainfall is less than this, irrigation is necessary at 25mm/week. The crop does not tolerate drought.
Soils
Strawberry plants are shallow rooted and they grow on a wide range of soils. However, deep sandy loams which are well drained and rich in humus are ideal. It requires soil pH should be 5.5-6.5and should not be grown in saline soils.
Varieties
The current varieties grown in Kenya include: Chanderler, Douglas, Aiko and Cambridge Favourite.
Land preparation
Before planting, work the soil so that there is a deep and reasonably loose planting bed.
Propagation and planting
Splitting is the most common method used to propagate strawberries. Runners are also used especially in temperate countries. Healthy plants should be used to start the crop.
When splitting the plants, trim the bottom of the crown, leaving only the parts of the crown with white roots. The preferred planting time in the tropics is the rainy season.
Spacing
Spacing is 45 x 30cm between and within rows giving a plant population of 74,000 plants/ha. Vigorous varieties are spaced at 90 x 30cm (55,000 plants/ha). The crown is very short and will not tolerate deep planting. Roots should not be allowed to dry out and should be carefully spread in the planting hole.
Straw berry plants
Nutrients/ Fertilizers
At planting apply 200kg/ha of Double Super Phosphate and 150kg/ha of Ammonium Sulphate Nitrate (26% N) at flowering. High soil organic matter increases yields. Therefore manure should be applied during the land preparation.
Mulching
Straw, black polythene and rice husks are used as mulch. The mulch reduces weeds, conserves moisture and keeps the fruits clean.
FIELD MANAGEMENT
Deflowering:
This is necessary to control premature cropping which is induced by short day conditions occurring in Kenya. The plant starts flowering before it is established. Deflowering is recommended for the first 2 months until the crop establishes itself. After the 2months, bud clusters should be left to develop and set fruit. These will reduce chances of early exhaustion of the plant.
Stripping/pruning
During the rest period all old and diseased leaves are removed off the plant to reduce source of infection from diseases or pests and to allow re-growth of foliage. Removed leaves should be collected and burnt outside the field. Cut off runners regularly except for those needed for planting. One or two runners from the runner types can be rooted for the next planting. Thinning to 2- 3 splits per crown should be done every 7 months to allow rejuvenation, this increases strawberry yields.
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DISEASES
Integrated disease management techniques are highly recommended in strawberry growing. These include choice of sites with good drainage, disease free, with good air circulation and with no shading. Field sanitation should be maintained through removal of plant debris. Excessive use of nitrogen fertilizers should also be avoided as this result in excessive vegetative growth making the plants more susceptible to diseases. Mulching can also be used to minimize fruit rots.
| Disease | Symptoms | Control |
| Leaf Spot (Mycosphaerella spp) | Grey spots with purple margins on upper surface of leaves. On fruits superficial black spots may form during wet weather | Destroy residues after harvest,Practice crop rotation
Use recommended fungicides e.g Antracol, Milthane super, Topsin M |
| Botrytis fruit rot (Grey mould)(Botrytis cinerea) | One to several blossoms in a cluster may show blasting (browning and drying) that may spread down the pedicel. Fruit infections usually appear as soft, light brown, rapidly enlarging areas. If the infection remains on the plant, the berry usually dries up, mummifies and becomes covered with a gray, dusty powder. | Mulching of the plantsUse recommended fungicides as in leaf spot |
| Verticilium wilt (Verticillium dahlia) | The outer and older leaves drop, wilt, turn dry, and become reddish yellow or dark brown at the margins and between veins. | Practice crop rotation and avoid areas where potatoes, tomatoes, eggplant plants have previously been grown. |
| Angular leaf spot (Xanthomonas spp) | Initially appear as minute water-soaked lesions on the lower leaf surface. Eventually, lesions become visible on the upper leaf surface as irregular, reddish brown spots. | Practice crop rotationUse healthy planting material
Use recommended fungicides as in leaf spot |
| AnthracnoseColletotrichum
acutatum |
Affected stems are sometimes girdled by lesions. On fruit, symptoms first appear as whitish, water soaked lesions which turn brown and enlarge within two to three days to involve most of the fruit. Lesions are covered with salmon-colored spore masses. Infected fruit eventually dry down to form hard, black, shriveled mummies. The entire plant may wilt and die | Maintain field hygiene |
STRAWBERRY PESTS
| Pest | Damage | Control |
| Flower Thrips (Frankliniella occidentalis) | Blemished seeds on achenes and uneven fruit maturity | Scouting for the flower thrips should be done regularly. Control is warranted if populations exceed 2 to 10 thrips per blossom.Use selective insecticides e.g Neem based to avoid killing pollinators.
Insecticide should be applied pre-bloom or before 10% of the plants have open blossoms. |
| Strawberry Bud Weevilor Strawberry Clipper (Anthonomus signatus) | Nearly mature blossom buds are injured by adult clippers that puncture buds with their snouts, girdle the flower buds and then clip the stem below the buds. Clipped buds hang down or fall to the ground. | Early cultivars are usually damaged more than later ones hence planting 2 or 3 rows of an early cultivar as a trap crop around the perimeter of each field has been suggested as a way to reduce overall damage or to concentrate the adults for control by use of an insecticide only in the trap crop. |
| Slugs (Agriolimax spp) | Slugs damage fruit by chewing deep ragged holes into the surface of berries, especially under the cap. | Use of traps |
| Strawberry Root Weevil (Otiorhynchus ovatus) | Plants are weakened, stunted, or killed by the larvae of root weevil, which are grubs that feed on strawberry roots and crowns. | Control measures should be directed toward the adult stage after scouting for their presence. Use recommended insecticide e.g. Actara, Confidor. |
| Meadow Spittlebug (Philaenus spumarius) | Spittlebugs pierce the plant and suck on sap, which can result in reduced plant vigor, stunting and decreased yield. | Use of recommended insecticides e.g Atom 2.5EC, Decis, Evisect S, Karate, Achook EC |
| Two-Spotted Spider Mite (Tetranychus urticae) | Mottling, speckling, or bronzing of foliage is caused by spider mites feeding on plant sap by rasping and sucking on leaf surfaces, which destroys leaf chlorophyll. | use recommended miticide e.g. Omite, Talstar 50EC, Kelthane, Dynamec 1.8 EC for if 25% of the leaflets (15 out of 60) are infested by one or more mites |
| Nematodes(Pratylenchus spp and
Meloidogyne spp |
Strawberry plants infested with nematodes may be stunted and show symptoms of mineral deficiencies and water stress, particularly as the berries form | Use of Use recommended Nematicide e.g Morcap, Nemacur |
Strawberry disease symptoms
- a) Black seed disease b) Leaf spot
- c) Phomopsis leaf blight on strawberry d) Phomopsis fruit rot
- e) Angular leaf spot (bacterial blight) symptoms on lower leaf surface
- f) Angular leaf spot (bacterial blight) symptoms on upper leaf surface
Angular leaf spot symptoms on strawberry calyx
Verticillium wilt on strawberry, the outer leaves dry first
Botrytis fruit rot (gray mold Botrytis fruit rot (gray mold) on strawberry
Anthracnose lesion on strawberry Powdery mildew on strawberry
Strawberry pests
Damage by thrips on strawberry Strawberry flower thrips
Adult strawberry clipper Strawberry clipper damage
Strawberry sap beetle Strawberry sap beetle damage
Slugs and their damage Root weevil life stages: egg, larva, pupa, adult.
Strawberry rootworm adult Spotted spider mite damage
Rootworm damage Meadow spittle bug damage
Meadow spittle bug
HARVESTING
Harvesting of strawberry fruits starts 2½months – 3months after planting depending on variety and the plant can produce fruits for up to three years continuously. Strawberry fruits should be picked in the early morning preferably as soon as they are dry. They should be carefully handled to avoid bruising which promotes disease infections and reduces marketability. Fruits for export should be harvested when they are 1/4 ripe to avoid over-ripening when they are on the market. The lifespan of the crop is 3 years.
Yield