Strawberry

Description

Strawberry is the name given to several plant species in the genus Fragaria, including Fragaria vesca (wild strawberry), Fragaria grandiflora, Fragaria magna, Fragaria chiloensis and Fragaria ananassa (or Fragaria x ananassa) which are grown for their edible fruit. Strawberry is an herbaceous perennial in the family Rosaceae. The plant has a short stem and trifoliate leaves which form a crown. close to the ground. The leaves display a variety of characteristic depending on the species, some are evergreen whereas some have leaves that will die and fall off in winter. The plant produces flower stalks from the crown and the the flowers are white in color. The fruit of the plant is red and fleshy with small seeds on the outside. Strawberry can grow 20–25 cm (8–10 in) in height and has an economic life of 2–4 years before the plants are replaced. Strawberry may also be referred to as garden strawberry and the plant is grown in most northern temperate regions of the world. The first domestic hybrids were created in Europe.


Uses

Strawberries are consumed as a fresh fruit or can be used to produce jams, jellies or preserves.


Propagation

Basic requirements
Strawberries grow very well in cool temperate climates, at temperatures below 30°C (86°F)and require at least 8 hours of sunlight per day. They can be grown successfully in a wide variety of soils from sandy soils to silty clay but will grow best in a deep, well draining loam rich in organic matter. The optimum pH for their growth is between 5.5 and 6.5. If drainage is poor then it is recommended to plant strawberry on beds raised by a minimum of 15–20 cm (6–8 in).

Strawberry varieties
Strawberries generally fall into 3 categories:
June-bearing
Evergreen
Day-neutral
June-bearing plants commonly produce large fruits, and, as their name suggests, will produce a crop of fruit over a 2–3 week period around June. Evergreen strawberry varieties produce two (and sometimes 3) crops of fruit per year in spring and late summer or early fall. Day-neutral strawberry varieties will give you fruit in the first year, generally produce smaller fruits but will produce whenever the temperature is between 1.6–29°C (35–85°F).

Propagation

Seeds
It is generally considered to be more difficult to start strawberry plants from seed than it is to work with young plants. Depending on the variety of strawberry you have chosen, it may be necessary to cold treat your seeds before germination. This can be achieved by simply placing them in the freezer for 2–4 weeks before sowing. Strawberry seeds should be sown in trays containing a good quality, sterile seed starting mix. Sow the seeds to a depth of 6 mm (0.25 in) and keep the soil moist (but not wet) while the seeds germinate. Seeds should germinate in 2–3 weeks. When the seedlings reach 2.5–5.0 cm (1-2 in) in height, thin the seedlings if they are too close together and repot or transplant to the garden when they have 3 leaves. If planting outside be sure to harden the seedlings off before you put them in the ground.

Runners
Strawberries produce offspring on a sideshoot known as a “runner”. Runners can be removed from the mother plant and relocated. Simply plant the runners to the desired final spacing in a bed prepared similarly to planting seeds.

Planting
Begin preparing the strawberry bed as early as possible in the Spring when the soil becomes workable. Prepare the soil for planting by adding organic matter such as compost or well-rotted manure. Plant the strawberry transplants 38–60 cm (15–24 in) apart depending on variety and allow 90–120 cm (36–48 in) between rows. Be careful to plant so that the crown of the plant (the point from which the leaves emerge) is at the soil surface. If planted too deep, the plants may rot and if planted too shallow the plants may not take root. After planting, water the plants thoroughly.

General care and maintenance
In the first growing season after planting, the plants should not be allowed to produce fruit in order for the plants to concentrate their energy of vegetative growth. Pinch off any flowers as they are produced. Fruit can be harvested in the year after planting. When the desired density of plants is reached cut off any runners or cultivate with a hoe. Weeds should also be removed from the strawberry bed regularly. Strawberry plants also require adequate moisture and should receive 2.5–3.8 cm (1–1.5 in) of water per week either from rainfall or irrigation if needed. Strawberries will benefit from the addition of mulch which helps to conserve soil moisture and protects the plants from late frosts in Spring. If frost is forecast after planting the plants should be protected with row covers or other suitable material. Plants can also be protected with sprinkler irrigation. Row covers can also be used to protect the fruit from birds when fruiting.

Harvesting
Fruit should be harvested regularly (every other day) when it is being produced by picking the berry along with the cap and 0.5 in of stem. remove the berries by pinching the stem. Harvest only fully ripe strawberries as they will not ripen further after harvest.


References

Bordelon, B. (2001). Growing strawberries. Purdue University Cooperative Extension Service. Available at: http://www.hort.purdue.edu/ext/ho-46.pdf. [Accessed 15 April 15]. Free to access.

Maas, J. L. (Ed.) (1998). Compendium of strawberry diseases. Second Edition. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopap.... Available for purchase from APS Press.

Strang, J. (2010). Strawberries. University of Kentucky Cooperative Extension Service. Available at: http://www.uky.edu/Ag/NewCrops/intros.... [Accessed 15 April 15]. Free to access.




Common Pests and Diseases

Spider mites (Strawberry spider mite)
Tetranychus turkestani

Symptoms
Leaves stippled with yellow; leaves may appear bronzed; webbing covering leaves; mites may be visible as tiny moving dots on the webs or underside of leaves, best viewed using a hand lens; usually not spotted until there are visible symptoms on the plant; leaves turn yellow and may drop from plant.
Cause
Arachnid
Comments
Spider mites thrive in dusty conditions; water-stressed plants are more susceptible to attack.
Management
In the home garden, spraying plants with a strong jet of water can help reduce buildup of spider mite populations; if mites become problematic apply insecticidal soap to plants; certain chemical insecticides may actually increase mite populations by killing off natural enemies and promoting mite reproduction.

Angular leaf spot
Xanthomonas fragariae

Symptoms
Very small water-soaked lesions on lower surfaces of leaves which enlarge to form dark green or translucent angular spots which ooze bacteria; lesions may coalesce to form reddish spots with a chlorotic halo.
Cause
Bacterium
Comments
Bacterium survives in crop debris and overwintering plants; can survive for long periods on plant debris but can not live free in soil; bacteria can be spread by splashing water.
Management
Use only certified planting stock; rotate crops and avoid overhead irrigation; chemical controls generally ineffective.

Anthracnose
Colletotrichum fragariae
Colletotrichum gloeosporoides
Colletotrichum acutatum

Symptoms
Leaf spot
Round black or light gray lesions on leaves; numerous spots may develop but leaves do not die.

Runners and petioles
Dark brown or black sunken, circular lesions on stems, petioles and runners; plants may be stunted and yellow; plants may wilt and collapse; internal tissues discolored red.

Crown rot
Youngest plant leaves wilt during water stress in early afternoon and recover in the evening; wilting progresses to entire plant; plant death; reddish-brown rot or streak visible when crown is cut lengthways.

Bud rot
Damp, firm dark brown to black rot on buds; plants with single buds may die; plants with multiple crown may wilt as disease progresses .

Flower blight
Dark lesion extending down pedicel which girdles the stem and kills the flower; flowers dry out and die; infection after pollination may result in small, hard, deformed fruit.

Fruit rot
Light brown water-soaked spots on ripening fruit which develop into firm dark brown or black round lesions.
Cause
Fungi
Comments
Plants that are planted in infected soil become infected by splashing water and soil; fungus survives in soil for up to 9 months.
Management
Fumigating soil may help reduce soil inoculum; solarizing soil may destroy soil inoculum; rotate to non-host crops if funigation or solarization is not possible; wash all soil from plant crowns prior to planting; weed around plants regularly; plant only disease free transplants; do not use excessive amounts of nitrogen fertilizer;

Gray mold (Botrytis fruit rot, Blossom blight)
Botrytis cinerea

Symptoms
Blossoms turning brown and dying; misshapen fruit; patches of rot on fruit which enlarge and often affects entire fruit; masses of gray mycelium on surface of rotting tissue; no leakage of fluid from fruit; fruit becomes dried and mummified.
Cause
Fungus
Comments
Disease emergence favored by extended periods of high humidity or leaf wetness during flowering and moderate temperatures.
Management
Remove and destroy all dead or infected material; remove decaying fruit; grow fruit under plastic; use plastic mulch to reduce fruit contact with soil; apply appropriate fungicides; plant in areas where wind will rapidly dry wet plants and fruit; plow crop debris into soil after harvest.

Leaf scorch
Diplocarpon earlianum

Symptoms
Irregular dark purple or brown blotches on upper leaf surface which may colaesce to produce large purplish brown patches; tissue between blotches may turn purple or red; lesions may also develop on flowers and fruits; affected petals may wither and drop from plant; lesions may girdle peduncles causing death of fruit.
Cause
Fungus
Comments
Disease emergence favored by wet foliage for extended periods of time.
Management
Plant resistant varieties; regular renewal of plants; plant in an area with good air circulation and drainage in full sun; remove all foliage from plants at harvest; application of appropriate foliar fungicide may be required to provide control.

Powdery mildew
Spaerotheca macularis

Symptoms
Patches of fuzzy white fungal growth on lower leaf surface which enlarge and coalesce; leaf edges curling upwards; purple-red blotches on lower leaf surface; deformed fruit may be produced if flowers become infected, severe infections may cause the plant to produce no fruit
Cause
Fungus
Comments
Fungus overwinters on leaves; spores spread by wind
Management
Apply protective fungicide e.g. sulfur at first signs of disease; plant resistant varieties; avoid overhead irrigation; remove dead leaves at harvest to decrease overwintering mycelium

Phomopsis leaf blight
Phomopsis obscurans

Symptoms
One to five circular, red-purple spots on leaflet; distinct zonal patterns on leaves with dark brown center surrounded by lighter brown and then purple, red or yellow; dark elongated and sunken lesions on petioles, stolons and fruit trusses.
Cause
Fungus
Comments
Disease occurs worldwide and can cause severe defoliation.
Management
Specific control measures not developed; remove older leaves after harvest; application of foliar fungicides after harvest may help control disease.

Leaf spot (Mycosphaerella leaf spot)
Mycosphaerella fragariae

Symptoms
Small round or irregular deep purple lesions on upper surfaces of leaves which enlarge and develop a gray-white center; lesions can grow large in susceptible varieties and the center of the lesion remains brown; lesions may also develop on fruit, petioles and stolons.
Cause
Fungus
Comments
Disease spread by splashing water.
Management
Plant disease free stock; apply protective foliar fungicide.

Armyworm (Beet army worm, southern armyworm)
Spodoptera exigua
Spodoptera eridania

Symptoms
Singular, or closely grouped circular to irregularly shaped holes in foliage; heavy feeding by young larvae leads to skeletonized leaves; shallow, dry wounds on fruit; egg clusters of 50-150 eggs may be present on the leaves; egg clusters are covered in a whitish scale which gives the cluster a cottony or fuzzy appearance; young larvae are pale green to yellow in color while older larvae are generally darker green with a dark and light line running along the side of their body and a pink or yellow underside.
Cause
Insect
Comments
Insect can go through 3–5 generations a year.
Management
Organic methods of controlling armyworms include biological control by natural enemies which parasitize the larvae and the application of Bacillus thuringiensis; there are chemicals available for commercial control but many that are available for the home garden do not provide adequate control of the larvae.

Loopers (Cabbage looper)
Trichoplusia ni

Symptoms
Large or small holes in leaves; damage often extensive; caterpillars are pale green with a white lines running down either side of their body; caterpillars are easily distinguished by the way they arch their body when moving; eggs are laid singly, usually on the lower leaf surface close to the leaf margin, and are white or pale green in color.
Cause
Insect
Comments
Insects overwinter as pupae in crop debris in soil; adult insect id a dark colored moth; caterpillars have a wide host range.
Management
Loopers populations are usually held in check by natural enemies; if they do become problematic larvae can be hand-picked from the plants; an organically acceptable control method is the application of Bacillus thuringiensis which effectively kills younger larvae; chemical sprays may damage populations of natural enemies and should and should be selected carefully.

Thrips (Western flower thrips)
Frankliniella occidentalis

Symptoms
Damage to strawberry flowers, including browning of anthers and stigmas; insects may be numerous on fruit and may cause bronzing around the cap; insect is small (1.5 mm) and slender and best viewed using a hand lens; adult thrips are pale yellow to light brown and the nymphs are smaller and lighter in color.
Cause
Insect
Comments
Thrips population builds up in spring on weeds and a number of crops and migrate to strawberries when crops are harvested or when weeds dry up.
Management
Avoid planting next to onions, garlic or cereals where very large numbers of thrips can build up; use reflective mulches early in growing season to deter thrips; apply appropriate insecticide if thrips become problematic.

Weevils (Strawberry root weevil, Rough strawberry root weevil, Black vine weevil)
Otiorhynchus spp.

Symptoms
Notches in leaves of plants; plants stunted and dark in color with closely bunched leaves; adult insect is a snot-nosed beetle which can vary in color from dark to light brown depending on species; larvae are cream-white colored grubs which feed on roots below ground.
Cause
Insect
Comments
Damage within a field usually affects a circle of plants; weevil attack is sporadic and can be very damaging.
Management
Keep strawberry beds free of weeds and grass; avoid planting close to woodland or blackberry or elderberry which may harbor weevil populations; pesticide sprays or dusts which contain pyrethroids are effective at controlling strawberry weevils.

Japanese beetle
Popillia japonica

Symptoms
Leaves skeletonized (only veins remaining); flowers and buds damaged; plant damage may be extensive; adult insect is a metallic green-bronze beetle with tufts of white hair protruding from under wing covers on each side of the body; adult beetles are approximately 13 mm in length; larvae are cream-white grubs which develop in the soil.
Cause
Insect
Comments
One beetle generation every 1-2 years; pheromone traps may actually attract more beetles to home gardens and should generally be avoided; beetle overwinters as larvae in soil; beetle has an extensive range of over 300 host plants.
Management
If beetles were a problem in the previous year, use floating row covers to protect plants or spray kaolin clay; adult beetles can be hand picked from plants and destroyed by placing in soapy water; parasitic nematodes can be applied to soil to reduce the number of overwintering grubs; insecticidal soaps or neem oil can help reduce beetle populations.

Aphids (Peach aphid, Potato aphid, Melon aphid, Strawberry aphid)
Myzus persicae
Macrosiphon euphorbiae
Aphis gossypii
Chaetosiphon fragaefolii

Symptoms
Small soft bodied insects on underside of leaves and/or stems of plant; usually green or yellow in color, but may be pink, brown, red or black depending on species and host plant; if aphid infestation is heavy it may cause leaves to yellow and/or distorted, necrotic spots on leaves and/or stunted shoots; aphids secrete a sticky, sugary substance called honeydew which encourages the growth of sooty mold on the plants.
Cause
Insects
Comments
Aphids transmit several viruses which can be very damaging to strawberry, the insects rarely reach a high enough population to cause severe damage directly but the spread of viruses is a major concern in strawberry production.
Management
If aphid population is limited to just a few leaves or shoots then the infestation can be pruned out to provide control; check transplants for aphids before planting; use tolerant varieties if available; reflective mulches such as silver colored plastic can deter aphids from feeding on plants; sturdy plants can be sprayed with a strong jet of water to knock aphids from leaves; insecticides are generally only required to treat aphids if the infestation is very high - plants generally tolerate low and medium level infestation; insecticidal soaps or oils such as neem or canola oil are usually the best method of control; always check the labels of the products for specific usage guidelines prior to use.

Slugs
Arion hortensis
Deroceras reticulatum

etc.

Symptoms
Irregularly shaped holes in leaves and stems;rough holes in ripe fruit; if infestation is severe, leaves may be shredded; slime trails present on rocks, walkways, soil and plant foliage; several slug and snail species are common garden pests; slugs are dark gray to black in color and can range in size from 2.5 to 10 cm (1-4 in).
Cause
Mollusc
Comments
Slugs prefer moist, shaded habitats and will shelter in weeds or organic trash; adults may deposit eggs in the soil throughout the season; damage to plants can be extensive.
Management
Practice good garden sanitation by removing garden trash, weeds and plant debris to promote good air circulation and reduce moist habitat for slugs; handpick slugs at night to decrease population; spread wood ashes or eggshells around plants; attract molluscs by leaving out organic matter such as lettuce or grapefruit skins, destroy any found feeding on lure; sink shallow dishes filled with beer into the soil to attract and drown the molluscs; chemical controls include ferrous phosphate for organic gardens and metaldehyde (e.g. Buggeta) and carbaryl (e.g Sevin bait) for non-organic growers.

Red stele (Red core)
Phytophthora fragariae

Symptoms
Stunted plant growth; old leaves withered and may have red yellow or orange tinge; new leaves small; little or no fruit produced and few runners; reddish discoloration of root core which may extend into the crown.
Cause
Oomycete
Comments
Can survive in cuttings and spread to new plants; disease emergence favored by wet or moist soils and cool, wet weather conditions; younger plants generally show more damage to roots.
Management
Plant only certified stock; avoid transferring soil and water contaminates sites; avoid planting in areas with a history of red stele; plant in raised beds to improve drainage; if disease is present apply appropriate fungicide.