Blackberry

Rubus spp.

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Description

Blackberry, is a perennial shrub in the family Rosaceae that is grown for its aggregate black fruit of the same name. The name blackberry is used to describe several species, including Rubus fruticosis (wild blackberry), Rubus ursinus and Rubus argutus, two species native to North America. Blackberries have three stem types: erect, arching, and trailing. They often have thorns, but some varieties are thornless. The leaves alternate along the stem with each group of leaves consisting of 3–5 leaflets. The leaves are prickly and bright green, and are toothed along the edges. The life-span of blackberry shrubs is variable, but they usually live for less than ten years reaching heights of up to 3 m (10 ft). Blackberry may also be referred to as bramble and the shrubs grow native on every continent except Australia and Antarctica.

Uses

Blackberries are consumed as a fresh fruit. They can also be frozen or canned for later use in ice creams, juices, pies, jellies, preserves and jams and other sweet desserts. Blackberries are high in antioxidants and vitamins and are a good sources of potassium, phosphorus, iron and calcium.

Propagation


Basic requirements
Blackberries grow best in temperate regions with cool summers and mild winters as they are susceptible to cold weather. They grow best when daytime temperatures are around 25°C (77°F). Blackberries prefer full sun (minimum six hours of direct sunlight) and they need to be planted in soil that drains well, is high in organic matter, and has a pH range of 6–6.5. Drainage it critical in blackberry propagation as the plants are susceptible to root rot. Blackberries should not be planted in low lying areas where water may build up and they require a post support system or trellis to support the weight of the fruit on the plants. Blackberry canes are biennial and produce fruit in the second year of growth. Canes in their first year of growth are called primocanes and those in the second year of growth are called fruiting canes or floricanes. The young canes are green in color, whereas the older floricanes are tougher and have a woody covering making them easy to tell apart.

Preparation
Soil may need prepared up to two years in advance of planting if major amendments are required. Acidic soil can be amended with lime to bring the pH up to a level suitable for blackberries. Organic content can be increased by planting a cover crop or by the addition of manure or compost. Avoid planting blackberries where peppers, eggplant, tomatoes or potatoes have been grown previously as these plants are host to Verticillium fungi which can cause root rot in blackberries. Choose a variety which is suited to your region.

Planting and trellising
Many blackberry varieties are very vigorous and using a support system such as a trellis will help to protect the canes from wind damage while also supporting the weight of the fruit crop. The trellis should be constructed before or at planting to avoid damaging the young plants after they are in the ground. The traditional method of supporting red blackberry canes is a post and wire system. This method involves running two wires about 60 cm (2 ft) apart vertically between wooden posts staked into the ground. The lower wire should be positioned 90 cm (3 ft) from the ground and the upper 1.5 m (5 ft) from the ground. The blackberry canes can then be tied to the wires. A second option is a T-trellis which is similar to the post and wire but the vertical wooden posts each have two cross bars to attach the wire. Two sets of wires run parallel to one another, one above the other. The vertical posts should be spaced 3.6–4.6 m (12-15 ft) apart with the lower wire positioned 90 cm (3 ft) from the ground and the upper 1.5 m (5 ft) from the ground. Blackberry plants in the home garden are usually grown from bare root plants or from tissue-cultured plants and should be planted in early Spring when the danger of any severe frosts has passed. The plants are usually planted in a row and the suckers will fill in the spaces to produce a hedge. Plant approximately 70 cm (27.5 in) apart, allowing 2.4–3 m (8–10 ft) between rows.

Pruning
Allow the plants to fill in the row to a width of about 30–38 cm (12–15 in) during the course of the growing season. Remove any suckers which are produced outwith this row. After harvest, cut the fruited canes of summer-fruiting varieties to ground level. Select 6–8 of the strongest young canes on each plant and tie them to the supporting wires so that they are spaced 8–10 cm (3–4 in) apart. Cut all of the canes of Autumn fruiting varieties to ground level after harvest. Cut back canes as needed in the summer if required to prevent crowding.

Diseases

Anthracnose Fungus Elsinoe veneta

Symptoms

Small purple or red circular lesions on canes which enlarge and develop a sunken gray, cracked center; margin of lesions become raised and purple; lesions coalesce to form large discolored areas; canes may eventually be girdled and die back

Comments

Fungus overwinters in diseases canes; emergence of disease is favored by prolonged periods of wet weather and excessive overhead irriagation

Management

Cultural practices for controlling the spread of disease in the home garden include: avoiding excessive applications of nitrogen fertilizers, keeping areas surrounding plants free from weeds, avoiding overhead irrigation and watering only during the day, ensuring the plants have adequate time to dry out in the afternoon; commercial growers may require the use of fungicides for large plantations

Blackberry rosette (Double blossom) Fungus Cercosporella rubi

Symptoms

Flowers with distorted petals and enlarged sepals which gives the appearance of a double flower; unopened flowers are enlarged and redder than normal; shoots may have abnormal proliferations; no fruit is produced on infected branches

Comments

Wild blackberries can act as a reservoir for the disease; flowers of uninfected canes can become infected from those on infected canes and will show symptoms the following year

Management

The most effective method of controlling the disease is the use of resistant blackberry varieties; if plants are already infected but disease is not yet severe then remove and destroy any abnormal blossom clusters; old canes should be removed and destroyed immediately following harvest; fungicide application may limit damage; disease can also be controlled by only harvesting berries in alternating years, completely destroying the above ground part of the plants in the years in between; the planting may be split in two so that there is a harvest of fruit each year while the other half is cut back

Botrytis fruit rot Fungi Botrytis cinerea

Symptoms

Canes are bleached in appearance and develop flattened masses of black fungal fruiting bodies where grey mycelium and spores develop; flowers may become infected and become blighted by the fungus; infected drupelets on the fruit may develop a watery rot which is replaced by grayish brown fungal structures; if berries are left on the vines they become mummified

Comments

Emergence of Botrytis fruit rot is favored by cool and wet conditions; physical damage to fruit increases likelihood of infection

Management

Promote air circulation around vines by using trellises or training the vines; avoid over fertilizing plants; protective fungicides can be used to control the disease and should be applied at intervals of 7-14 days from early bloom right through to harvest

Crown gall Bacterium Agrobacterium tumefaciens

Symptoms

Galls on canes and branches above ground or on root system; galls have a rough surface and a spongy texture; galls may darken and develop cracks as they mature; galls may have little or no effect on growth but can cause a reduction in vigor and death of plants

Comments

Bacteria most commonly enter the plant through wounds created by pruning or from wind damage; the bacterium causes a proliferation of undifferentiated plant cells which form a gall

Management

Avoid planting in areas known to have been affected by crown gall for a period of a least three years; if an infected plant is found, destroy it immediately; a biological control agent called Galltron is available for use in blackberries which contains a nonpathogenic strain of Agrobacterium which is antagonistic to the bacterium which causes crown gall; roots of new plantings are dipped in the substance prior to planting to protect them

Japanese beetle Insect 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

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

Leafrollers (e.g. Omnivorous leafroller) Insect Platynota stultana

Symptoms

Leaves of plant rolled and tied together with silk webbing; feeding damage to rolled leaves; defoliation of plant; silk webbing may also be present on fruits and fruits may have substantial scarring from feeding damage; larvae wriggle vigorously when disturbed and may drop from plant on a silken thread

Comments

Adult insect is a moth which can fly over several miles to find suitable hosts; alfalfa and sugar beet are good hosts

Management

Monitor plants regularly for signs of infestation; remove weeds from plant bases as they can act as hosts for leafrollers; avoid planting pepper in areas where sugarbeet or alfalfa are grown nearby; Bacillus thuringiensis or Entrust SC may be applied to control insects on organically grown plants; apply sprays carefully to ensure that treatment reaches inside rolled leaves

Orange rust Fungus Gymnoconia peckiana

Symptoms

New growth is weak and spindly and lacks spines; leaves are stunted and distorted and are pale in color; waxy pustules develop on leaf undersides and turn orange and powdery; infected leaves eventually drop from the plant

Comments

Wild brambles and dewberries may act as a reservoir for the disease; fungus overwinters in the host plant

Management

Infected plants should be removed in entirety; prune and burn fruiting canes after harvest; improve air circulation around foliage by pruning and trellising vines; spread of rust can be minimized by applying foliar fungicides wen the orange spores are being produced; if well managed, the disease is not usually serious

Powdery mildew Fungus Podosphaera macularis

Symptoms

Light green chlorotic patches on foliage which later develops into powdery gray patches; leaves may be twisted or distorted; if infection is severe then shoots may become spindly with small leaves which cup upwards

Comments

Fungus overwinters in buds or on surface of canes; emergence of the disease is favored by warm, dry weather conditions

Management

If powdery mildew is known to be a problem in a particular area then avoid planting susceptible varieties; varieties bred in the US state of Arkanasas, such as Navaho, Apache, and Arapaho, are known to be quite resistant to powdery mildew

Rednecked cane borer Insect Agrilus ruficollis

Symptoms

Galls on canes which are usually 2.5-7.6 cm (1- 3 in) in length; canes may die over winter above the galls; bud break may be delayed the following spring; canes with galls often do not produce fruit; adult insect is a slender, metallic black beetle; larvae are white, flat-headed grubs

Comments

Female beetles deposit eggs on bark of canes and larvae burrow into primocanes

Management

Canes with galls should be pruned out and burned or buried to destroy overwintering larvae; remove any wild brambles nearby which may act as a reservoir for cane borer populations; if chemical treatment is required (generally if more than 5% of canes are affected) then it should be applied after bloom to limit damage to bees

References

CABI Crop Protection Compendium. (2008). Rubus datasheet. Available at: http://www.cabi.org/cpc/datasheet/47977. [Accessed 06 November 14]. Paid subscription required.

Ellis, M. A. & Converse, R. (1991) Compendium of raspberry and blackberry diseases and insects. American Phytopathological Society Press.

Fernandez, G. & Ballington, J. R. Growing blackberries in the home garden. North Carolina Cooperative Extension Service. Available at: http://www.ces.ncsu.edu/depts/hort/hi.... [Accessed 06 November 14]. Free to access.