Rural Industries Research & Development Corporation

Welcome to the LONG WHITE RADISH (DAIKON) chapter of RIRDC's major new publication (contents page here) on nearly 100 new rural industries.

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Introduction

The radish plant is erect, with a short, non-branching stem supporting leafy rosettes. It has a swollen tap root with narrow, round petioles and the mid-vein is light green in colour. The radish leaf is rich in carotene (pro-vitamin A) and calcium while the root is a good source of vitamin C and some potassium and dietary fibre. The leaf, root, seed pod and sprout are consumed as a vegetable.

Long white radish, which is one of four types of radishes, is the most extensive vegetable crop grown in Asia. The other types are twenty-day radish, leafy radish and sprout radish.

Markets and marketing issues

Long white radish imported into Japan is classified under `Salad beetroot, salsify, celeriac, radishes and other similar edible roots (07.06.90.000)' which shows that imported quantities are less than 500 t/year during the last four years from 1990-1994. Japan also imported 5 t of fresh radish from the Philippines at ¥106 per kg. (CIF). The wholesale price of Daikon in Tokyo Wholesale Markets provides an indication of the import prices for Daikon (Table 1 - not available in this html version).

Long white radish can be processed to give products such as pickles, dried and frozen radish.

Pickled radish comprised 32% of approximately A$6 billion of the Japanese pickle markets in the 1990s. Of these, takuan is the most popular processed form of pickled radish. The production of takuan has declined from 250,000 t in 1985 to 210,000 t in the early 1990s.

There are four types of takuan available in Japanese markets: pickling radish with rice bran (nakazuke takuan), pickling radish with miso (misozuke takuan), pickling radish with sake lees (kasuzuke takuan) and pickling radish with soy sauce (shozuzuke takuan). One form of pickling in which radish is the major ingredient, referred to as one-night quick pickling (ichiyazuke), has recently become popular in Japan.

Information in Japan on the importation of radish for takuan is unclear, e.g. in 1991 Japan produced 210,157 t of takuan but in the same year produced 1,692 t of dried radish as well as importing 30 t of fresh radish and 7,139 t of salted radish, making approximately 10,000 t of material for the production of takuan. The gap of approximately 200,000 t of takuan has raised a question mark about supply sources (Table 2 - not available in this html version).

Separate import statistics are not kept for takuan as it would be classified under `Materials for pickles' of which Japan imported 220,413 t valued at US$171 million in 1994.

Dried radish is used for cooking, soup, nigiri rice and `gobugobu' pickles. There are three types of dried radish available in Japanese markets, and they are fine sliced (usukiriboshi), long strip or ribboned (kiriboshi) and cross-cut (wagiriboshi). Production of dried radish in Japan has increased by more than 1,000 t in 1993 but the wholesale price has dropped to only ¥308 per kg (Table 2 - not available in this html version).

Dried radish imported into Japan is classified under `Vegetables -dried' of which 44,863 t were imported in 1994 valued at US$255 million.

Frozen radish is used mainly for Japanese traditional food `oden' (casserole) in which the root is cross-cut at approximately 10 cm in length, blanched and frozen by Individual Quick Frozen (IQF) technology.

Frozen radish is imported into Japan under `Other Frozen Vegetables [0710.80.090]' which includes lotus root etc. and has been dramatically increased from 85,416 t, valued at approximately US$140 million in 1994 to 99,896 t, valued at US$166 million in 1995.

Production requirements

Producing high quality radish during mid-summer and winter requires great care as high summer temperatures and strong sunlight prompt the roots to develop rapidly in size, and become pithy soon after maturity. Low temperatures slow vegetative growth, stimulate the forming flower buds and cause bolting in spring. Bolted radish is not marketable as the roots become woody and pithy. Therefore, the best time to grow long white radish is spring and early autumn.

Varieties

When selecting a radish variety, also check shape and colour, since market requirements vary with ethnic groups. The Chinese and Indo-Chinese require a white-necked, thin (5 cm diameter) root growing to 25 cm in length, but the Japanese fresh market prefers the green-necked, fat (7-10 cm diameter) radish grown to 30-35 cm in length.

For processing, the root shape is not as important but the flesh must be crunchy, and low in water content for faster drying. It must not be pithy. Radishes are marketed when the root mass is approximately 300-600 g, but depending on the type and market, they can be grown to even greater weights; a special Japanese variety called `Sakurajima' (shape 5) can be grown up to 20 kg. and a variety called `Moriguchi' (shape 8) can grow up to 120 cm long with a width of 2.5 cm (Fig. 1).

There are three other types of radish used in Asia which are:

Twenty-day radish Most commonly cultivated radish in Australia and other Western countries. There are several varieties, differing in size and shape, but they all produce relatively small roots of approximately 30-40 g and are coloured red, white or red/white. They are very fast growing, maturing in approximately 30 days in summer and 45 days in winter.

Leafy radish Grown as a leafy vegetable, this radish has large foliage and small roots. The plant is harvested when it has grown 10-15 leaves, each measuring 25 cm in length. The growing method is similar to twenty-day radish.

Sprout radish A specific variety that grows long, white stems. Seeds are sprouted in moist, dark conditions at approximately
20-25°C and grow to approximately 15 cm over ten days and are marketed after the roots are removed. The Japanese are heavy consumers of sprout radish under the name `Kaiware daikon' with approximately 15,000-20,000 t/year consumed in 1994.

Seeds of Chinese, Japanese and Korean radish cultivars are available in most Asian supermarkets in Sydney, Melbourne and Brisbane. They are also available from Australian seed companies, particularly the Japanese cultivars.

Agronomy

Depending on the cultivar, long white radish can germinate in soil temperatures as low as 5°C. The optimum growth temperature is 20-25°C. The seed is sown in rows at a depth of 5-10 cm. Dense sowing and early thinning will ensure a preferred plant population of 70,000-80,000 plants/ha. Excessive plant densities will result in small, irregular-sized and misshapen roots.

Growing times differ between varieties and seasons, being normally shorter in summer and longer in winter.

To produce high quality long white radish, plants must have adequate soil moisture throughout their development. Radishes are particularly sensitive to water stress, which causes pithiness in the root. Overhead sprinklers provide the moist environment required for radishes but also encourage fungal diseases, particularly in summer (not a favoured growing season).

Animal manure is normally applied in rows or broadcast. A good quality fowl manure should be applied six weeks before planting at the rate of 15 t/ha. (1.5 kg./m²⁾. Before planting, broadcast 1.5 t of chemical fertiliser G5 (N:P:K = 5:5:5) to ensure that the young seedlings have a ready supply of major elements immediately after germination. When the seedlings are established 3-4 weeks after sowing, thin them to 15-20 cm apart, side dressing with potassium nitrate after thinning if necessary. White radish needs to be grown 50-60 days in summer and 70-80 days in winter for the fresh market when the fresh root weighs approximately 0.5 kg.

Pest and disease control

Pre-germinate weeds before planting the crop and control them either with knockdown herbicides or by cultivation. It is usually sufficient to hand-weed fast-maturing vegetables like white radish once during their growth.

Radishes are attacked by the same pests as other members of the Brassica family. The most serious pests found in the New South Wales radish crops are cabbage white butterfly and aphids; nematodes and black beetle sometimes cause root damage.

The most important disease is bacterial soft rot (Edwinia carotovora), which is also found on other Brassica species. The bacteria are commonly found in decaying vegetable matter in the soil. They invade damaged tissue, often following other diseases. Hot, wet weather favours soft rot. A soft, mushy decay develops from the root ‘neck’ (near the ground) and eventually the entire root is affected by a very smelly soft rot. Soft rot can also be a postharvest problem. The disease is controlled by avoiding damage to the plant during side dressing or harvest, destroying diseased crop residues, and rotating the crop every three or four years.

Radishes are sometimes attacked by yellows (Fusarium oxysporum). The fungus survives for long periods in the soil, infecting the plant through roots and growing in the water-conducting tissues. Warm weather favours the disease. Affected plants lose vigour and the lower leaves on one side of the plant turn yellow; a brown discolouring develops under the skin of the root. The disease is controlled by using resistant varieties, and rotating crops every three or four years.
 

Harvesting and packaging

Radishes are susceptible to wilting. Harvesting is carried out during cool times of the day and the crop should be kept cool and moist until placed in cold storage at a temperature of 0°C and a relative humidity of 90%. The radish has a short shelf-life if pithiness develops inside the root.

Processing radishes are harvested approximately 10–12 weeks after sowing because processing cultivars need to be grown longer than freshmarket types. Roots are thoroughly washed by brush-washer machine or by hand and are prepared as per market requirements. To make takuan, all plants need to be dried for approximately 3–5 days in shaded areas with good ventilation for the roots to reduce to approximately 50% of their fresh weight. To make dried sliced radish, the leaf should be trimmed and roots are sliced and dried by either sun or in a drier until they are approximately 10% of their fresh weight. The dried radishes have a strong odour and packaging them in sealed plastic bags is desirable.
White radish is usually hand-harvested, then either tied in bunches of 2–3 roots per bundle or sold in bulk in cartons of five, 10 or 15 kg. Like other vegetables, radishes are susceptible to wilting. If possible harvest them when it is cool, preferably in the early morning, and keep the produce cool and moist until placed in cold storage.

In hot weather, pre-cool the crop to its optimum storage temperature as soon as possible after harvesting. This is best done with forced-draught air-cooling. Vacuum cooling benefits produce with a high, surface area-to-volume ratio, where rapid cooling is important, such as leafy vegetables.

Ideal storage conditions for radish are a temperature of 0°C and a relative humidity of  90–95%, but you must not freeze the produce as it can suffer extensive damage when thawing. These precautions should maintain the quality of the radish and increase its storage life.

Precautions with pesticides

Key contacts

Mark Hickey
NSW Agriculture
Yanco Agricultural Research Institute
Yanco, NSW 2703
Phone: (02) 6951 2765
Fax: (02) 6951 2600

Professor David Midmore
Biology Department
Central Queensland University
Rockhampton, Qld 4702
Phone: (07) 4930 6870
Fax: (07) 4930 9209

Dr Wendy Morgan
Agriculture Victoria
Private Mail Bag 15
South East Mail Centre, Vic. 3176
Phone: (03) 9210 9222
Fax: (03) 9800 3521

John Burt
Department of Agriculture
3 Baron Hay Court
South Perth, WA 6151
Phone: (08) 9368 3211
Fax: (08) 9367 2625

Dr T.K. Lim
Department of Primary Industries and Fisheries
GPO Box 990
Darwin, NT 0801
Phone: (08) 8999 2222
Fax: (08) 8980 0249
Email: tk.lim@dpif.nt.gov.au
 

References

Nguyen, V.Q. 1992 Growing Asian Vegetables Agfact H8.1.37.

Pan, C. 1996 Fresh and Processed Asian Vegetables RIRDC Research Paper No. 95/14.

Vinning, G. 1996 Market Compendium of Asian Vegetables RIRDC Research Paper No. 95/12.
 

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