Horseradish

Description

Horseradish, Armoracia rusticana, is an herbaceous perennial plant in the family Brassicaceae that is cultivated for its large, edible root. The leaves of the plant grow in a distinctive rosette pattern sprouting from single or multiple stems. The leaves have long petioles and can be smooth or crinkled, reaching 30–100 cm (12–40 in) in length. The taproot is thick and fleshy and cylindrical in shape and can reach 50 cm (20 in) in length. The plant produces many white flowers on racemes. Horseradish plants are usually grown as annuals, surviving only one growing season and can reach a height of 1.5 m (5 ft). Horseradish may also be referred to as red cole or pepper rod and originates from south-eastern Europe and western Asia.


Uses

Horseradish is grown as a vegetable and can be eaten fresh or cooked. Due to its bitter taste, it is commonly used to make sauces which accompany meat or fish.


Propagation


Basic requirements
Horseradish grows best in temperate climates in full sun or partial shade at temperatures between 15.5 and 28°C (60–65°F) . If grown as an annual, the plant requires a long growing season with a warm summer and cooler temperatures in late summer and fall to allow the flavor to develop in the root. Horseradish can be grown in most soils as long as they are well draining but will grow optimally in a deep, fertile, well-draining soil with a pH between 6.0 and 7.5.

Propagation
Horseradish is usually vegetatively propagated by dividing crowns or from root cuttings. It can be grown from supermarket bought root as it is not treated with any chemicals that affect growth. The disadvantage is that the variety and characteristics may not be known. Root pieces are small, pencil size pieces of root which grow from the main root. They are referred to a sets and as the horseradish root exhibits polarity, it is important to make a note of which end of the set is the top and which is the bottom in order to plant the piece the correct orientation. A good way of doing this is to use a straight cut across the top end of the set and an oblique cut at the bottom. If planting by dividing an established crown, the plant should be carefully dug from the soil and split into four equal pieces each with some leaf and root.

Planting
Horseradish sets should be planted as soon as the soil is workable in the spring. The soil should be prepared for planting by double digging and incorporating composted organic matter and all purpose fertilizer. The root sets can be planted in shallow trenches which are approximately 10 to 12 cm (4-5 in) allowing 45–60 cm (18–24 in) between individual plants and deep and at least 30 cm (1 ft) between rows. The sets should be planted at a 45° angle so that the top of the set is higher in the soil than the bottom end.

General care and maintenance
Horseradish should be provided with approximately 1 to 2 inches of water each week. Additional irrigation may be required during dry spells. Care should be taken not to overwater the plants or allow them to become too dry as this will affect the flavor of the harvested root. An additional dose of fertilizer high in potassium and phosphorous but low in nitrogen should be applied 4 to 8 weeks after planting. Excess nitrogen should be avoided as it will encourage too much top growth on the plants and will also cause the roots to branch. Horseradish plants will benefit from the addition of a layer of organic mulch which will help to suppress weed growth. I f no mulch is added then any weeds around young horseradish should be removed by gently cultivation the soil around the plants. Many growers make use of the practice of lifting and suckering their horseradish plants. Once the plant has begun to grow, it is gently lifted to expose the crown and any branching roots are removed. This focusses the plants energy on growing the main root.

Harvesting
Horseradish should be harvested when the tops have been frozen back in the fall. In commercial fields, the tops of the plants are mowed back to facilitate mechanical digging. In the home garden, the roots can be dug up with a fork and the tops removed after harvest. The roots should be scrubbed clean before storing. Leaving some small pieces of root in the ground will allow the plant to regrow the following year. If regrowth is not desired then all pieces of root should be dug up and removed to prevent the horseradish becoming a weed in the garden.





References

Bratsch, A. Speciality Crop File: Horseradish. Virginia Cooperative Extension. available at: https://pubs.ext.vt.edu/438/438-104/4.... [Accessed 19 December 14]. Free to access.

CABI Crop Protection Compendium. (2008). Armoracia rusticana datasheet. Available at: http://www.cabi.org/cpc/datasheet/7174. [Accessed 19 December 14]. Paid subscription required.

Drost, D. (2010). Horseradish in the Garden. Utah State Cooperative Extension. Available at: https://extension.usu.edu/files/publi.... [Accessed 19 December 14]. Free to access.




Common Pests and Diseases

Brittle root
Spiroplasma citri

Symptoms
Poor growth of plants; chlorotic leaves which collapse and dry out; roots are brittle and discolored dark brown with a dark ring when snapped in two
Cause
Bacteria
Comments
Disease is transmitted by beet leafhoppers; disease is one of the most destructive of horseradish
Management
Brittle root can be reduced or eliminated by controlling the insect vector; plants should be scouted for beet leafhoppers and appropriate insecticides should be applied

Bacterial leaf spot
Phytomonas campestre armoraciae

Symptoms
Small translucent spot on leaves which turn black and are scattered over the leaf surface between the veins; spots may enlarge after periods of rainfall; leaves may curl and dry up
Cause
Bacterium
Comments
Bacteria overwinter on plant debris; disease emergence is favored by wet weather
Management
Remove plant debris from around plants and after harvest to reduce overwintering inoculum

Cercospora leaf spot
Cercospora amoraciae

Symptoms
Round or angular tan spots with lighter centers on leaves; leaves dying and plants becoming defoliated
Cause
Fungus
Comments
Emergence of the disease is favored by periods of cool, wet weather; fungus is spread by splashing water
Management
Infected plant should be removed and destroyed to prevent spread; remove any volunteer plants and weeds; avoid working with plants when they are wet; seeds can be treated with hot water to eliminate the fungus prior to planting

Ramularia leaf spot
Ramularia cynarae

Symptoms
Disease initially appears as yellow-green circular patches between leaf veins which become distinct lesions with irregular margins; centers of lesions may dry out and drop from plant producing a shot hole appearance; if infection is severe, the entire leaf may dry out
Cause
Fungus
Comments
Fungus overwinters on plant debris
Management
Remove weeds and any horseradish debris from around plants; avoid the use of sprinklers for irrigation; remove and destroy any infected plants to prevent spread; rotate crops away from horseradish for a period of 3 years; if disease is problematic it may be necessary to treat with appropriate fungicides

White rust
Albugo candida

Symptoms
Pale yellow areas on upper leaf surfaces followed by the appearance of creamy white pustules on leaf undersides; if infection is severe then leaves may become curled and distorted with pustules covering the entire leaf surface
Cause
Fungus
Comments
Spores are spread by wind; fungus overwinters in plant debris or on perennial plants; disease development is favored by cool weather and periods of extended rainfall
Management
Remove weeds and any horseradish debris from around plants; avoid the use of sprinklers for irrigation; remove and destroy any infected plants to prevent spread; rotate crops away from horseradish for a period of 3 years; if disease is problematic it may be necessary to treat with appropriate fungicides

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
Horseradish can tolerate a large amount of damage; looper 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

Flea beetles (Horseradish flea beetle)
Phyllotreta armoraciae

Symptoms
Small holes or pits in leaves that give the foliage a characteristic “shothole” appearance; young plants and seedlings are particularly susceptible; plant growth may be reduced; if damage is severe the plant may be killed; the pest responsible for the damage is a small (1.5–3.0 mm) dark colored beetle which jumps when disturbed
Cause
Insects
Comments
Flea beetles may overwinter on nearby weed species, in plant debris or in the soil; insects may go through a second or third generation in one year
Management
Horseradish can tolerate a large amount of early feeding damage before the root is affected; application of a thick layer of mulch may help prevent beetles reaching surface; application on diamotecoeus earth or oils such as neem oil are effective control methods for organic growers; application of insecticides containing carbaryl, spinosad, bifenthrin and permethrin can provide adequate control of beetles for up to a week but will need reapplied

Mosaic
Turnip mosaic virus (TuMV)

Symptoms
Green and yellow mottling on leaves; crinkled, underdeveloped leaves; black streaks on petioles
Cause
Virus
Comments
Plant can tolerate low levels of infection