Rural Industries Research & Development Corporation

The New Rural Industries
A handbook for Farmers and Investors

Wasabi

Introduction

Wasabi (Wasabia japonica Matsum) is a perennial herb belonging to the same family of plants as broccoli, cabbage and mustards, the Brassicaceae. In its natural environment in Japan it grows alongside mountain streams. Superficially, the plant resembles a Brussels sprout stem without the Brussels sprouts. It is evergreen and forms large clumps if left undisturbed. Wasabi can be grown in raised gravel-beds above fast-flowing streams or in soil in a similar manner to other brassicas. A major limiting factor is its need for shade which raises production costs substantially.

Used with traditional Asian foods such as sushi and soba noodles, wasabi is in short supply in Japan because the younger generation is losing interest in continuing family farming traditions, farming space is diminishing under urban encroachment and problems are arising from pollution.

The major draw-card for Australian wasabi production is our ability to supply in the off-season market in South-East Asia. There is also a large domestic market for processed and, in particular, fresh wasabi for the restaurant trade.

So far wasabi has been grown in trial plots in areas in Tasmania suited to vegetable production. It is believed that parts of Victoria and some parts of highland New South Wales will also be suitable.

Marketing issues

Japan is seen as the principal potential market for Tasmanian production, with the possibility of smaller markets in Korea and Taiwan. Current Japanese production is around 5000 tonnes (fresh weight) per annum. Additional opportunities also exist for import replacement in the Australian domestic market. There is a strong demand for high-quality, fresh produce by the Japanese catering and food industry. Fresh roots fetch up to $AUD100/kg on the domestic Japanese market during the colder months. This demand currently cannot be met because of the progressive contraction of traditional production sites as a result of pollution and urbanisation. While there is a high demand for fresh quality stems, a major market also exists for processed product in the form of pastes, purees and powder.

Production requirements

Wasabi grows naturally under heavy shade provided by overhanging bushes on the edge of mountain streams. In Japan, shading of commercially grown wasabi varies from no shade at all to 80% block-out of incident light. Currently the level of shading used in Tasmanian trials has averaged between 65% for soil-grown and 80% for aquatic wasabi. The shade-cloth used has been 70% black although work is under way to test other weights and colours and the consequent effects on the plants. If the plant is exposed to too much radiation, the leaves will be scorched and/or the plant will exhibit physiological wilting.

Soil culture. Wasabi grows best on soils with an open friable structure and good drainage is essential. The preferred soil types are:

• deep alluvial loam, sandy loam or sandy clay loam;

• red soils such as Krasnozems or similar basalt derived red soils which drain freely;

• sandy soils which are high in organic matter (but which as yet have not been used for trial work).

Plants from this type of production system are commonly used for processing, although New Zealand has successfully produced fresh-quality product from soil culture. Being a Brassica, wasabi is susceptible to many of the bacterial diseases and some pests known to affect most other brassicas. Extreme air temperatures and soil conditions are the major limitations to wasabi production and may determine a plant's susceptibility to pest and disease attack.

Aquatic culture. Wasabi is produced in large quantities in Japan in aquatic production systems. The stems produced in this manner fetch the highest returns for the fresh market and are reportedly larger and of much higher quality. Important variables in aquatic production include temperature, clarity, oxygen saturation and nutrient status of the water. The water temperature range of 2.3 to 19.5ºC experienced in Tasmanian trials may have been too variable. The recommended temperatures are between 12º and 15ºC.

Varieties

Current trials have used Daruma, Daruma Improved (from New Zealand) and Tainon No.1 (from Taiwan) cultivars. Indications have been that Daruma and Daruma Improved will be suitable for Australian conditions. There is very little material available at this stage in Australia for commercial use. It is hoped that several new varieties will be available in late 1997 for further assessment.

Agronomy

Wasabi is easily stressed and the best times to plant are most likely autumn and spring when temperatures are moderate. Autumn is preferred as it naturally follows on from seedling production. The Soil culture. Once a site has been chosen it needs to be cleared of weeds entirely and shade needs to be constructed, taking into account any machinery that may need to be used within the shade structure such as tractors or irrigators. The shade-cloth has an important function in cooling the plants, which prefer to be between 12º and 20ºC but can handle quite bright light. This means that the shade structure design should allow good air-flow for cooling. Leaving the lower section open up to around half a metre would help to provide additional ventilation and cooling. Ideally the shade structure for soil grown wasabi should be simple for easy relocation. This will allow for crop rotation and prevention of disease build-up.

Aquatic culture. Beds need to be constructed from medium-grade gravel and raised to approximately 20-30cm in height and parallel with the direction of water flow. Plants should be planted down each side of the beds to allow roots to reach down into the wettest zone of the gravel but to prevent the stem from being submerged. Shade structures should be constructed as for soil culture. Wasabi will not grow in stagnant water or water of low oxygenation; therefore a year-round water supply of constant flow and temperature is necessary for an aquatic site.

There is little information on the specific nutrient requirements of wasabi. In Japan, soil-grown wasabi is fertilised with compost such as rape-seed cake and liquid manure. No nitrogen is applied to the young seedlings when first planted in the soil. For water-grown wasabi, a slow-release fertiliser composed of 12:12:12 (N:P:K) is applied monthly to the headwaters at a rate of 1 t/ha. Also, sulphur sprays are often applied to correct deficiency and to enhance flavour.

High-quality wasabi should grow at an even rate. This means that a number of small applications of nitrogen over the growing season should be applied. The amount applied will depend on the history of the site and its organic nitrogen levels. Phosphate fertiliser should be incorporated into the soil before planting, using a banding method of application. Once again a soil test will indicate the amounts needed. Regular leaf analysis and monitoring of nutrients will also help in fertiliser application.

Brassica crops are particularly sensitive to boron and molybdenum deficiency. It is likely that wasabi also needs these elements although nothing has been reported in the literature. In the first season before tissue-testing takes place, boron should be applied, for example, as borax at 20 kg/ha when broadcast and 10 kg/ha when placed in a band. Molybdenum can be supplied as sodium molybdate at 1 kg/ha or as a foliar application of sodium molybdate at 5 L/ha.

Irrigation of wasabi has two important functions:

• to maintain soil moisture levels

• to assist cooling of the plants.

Wasabi likes its roots to be kept moist but not to saturation point as this significantly reduces the amount of oxygen available to the plant and thereby restricts its function and growth. Tensiometers are very useful for this purpose, but the most important rule is to remember that little and often is better than one large dose.

Pest and disease control

Prevention, identification and management of disease is extremely important ( a review of wasabi pests and diseases is given in Chadwick). Wasabi is susceptible to a range of bacteria, fungus and viruses. Important features to watch for include leaf spots, blackening, yellowing of leaf or petiole veins, physical damage, wilting or drooping, mushrooms in soil, mould on stems or leaves. Bacteria which infect wasabi include Erwinia and Pseudomonas; Fungi include Phoma sp., Sclerotinia sp., Peronospora sp., Albugo sp. and Alternaria sp.

Pests of wasabi cause damage in many ways. Feeding removes valuable leaves and stems, physical damage promotes disease and reduces stem quality and aphids can transmit viruses. Symptoms to look for include; holes in leaves and grubs, aphids on underside of leaves, leaf puckering, slugs and snails at ground level under decaying leaves or clods, grubs in the growing point of plants and leaf silvering or skeletonizing. So far, various means of chemical control have been used against the two main problems found in wasabi which are aphids and white rust. Identification of more environmentally sound means of control will continue.

Harvest, handling and postharvest treatments

The whole plant is harvested or the plant is cut just below soil level with some roots intact. The stem usually reaches a marketable size of 8 to 15 cm long and 50 g or more by 18 to 24 months after planting. The price traditionally peaks during our summer months of January and February, which coincides well with anticipated harvest time. However, this may vary from year to year. The wasabi will tend to develop large side-shoots in autumn so it is best to harvest before these enlarge.

Presentation. Colour: generally the Japanese wasabi is dark green. Wasabi that is either lighter (yellow-green) or darker (brown-green) is considered inferior though still marketable. One of the most important aspects of colour is that the inside of the stem should be pale green to ensure a good coloured paste when the stem is ground.

Shape: wasabi should have an evenly tapered stem. Uneven taper shows that the wasabi has been grown under varying environmental conditions and will not fetch the best prices on the fresh market.

Trimming: trimming is a critical part of wasabi stem presentation. Excessive trimming shows that the stem was soil-grown or there was disease present, while insufficient trimming suggests they are not getting value for money (i.e. by including lower-value petioles or roots). High-value wasabi stems have the roots removed but the base of the stem is left intact. Wasabi imported into Japan with the base removed indicates that the plant has been grown in the soil and the stem removed for quarantine purposes. Petiole trimming is also important. Trimmed too long and the market will consider you have `weighted' the consignment with excessive low-value petiole. Trimmed too short and the perception will be that you have removed disease or the stems have been stored excessively long. Generally, petioles should be trimmed evenly to a length approximately one third the length of the stem, though this can vary between markets.

Weight: generally stems over 50g are preferred for the fresh market.

The storage of wasabi is still being investigated, although initial indications are that the best method is wrapping in a damp towel and placing in a refrigerated store. This will keep the stems fresh for several days.

Economics of production and processing

Soil culture. A model was developed to examine the feasibility of establishing a wasabi enterprise. The standard soil-culture model for comparative purposes assumed that the yield of stem material was 8t/ha, and that all the product was sold for $8/kg and later processed. No product was sold at the premium fresh-material price. In addition 2t/ha of stems was sold at $2/kg.

The net income for the enterprise was $68,000 per ha. Once established, the projected margin before overheads is $53,310/ha and based on a 1 ha development the net cash flow is $26,810 after allowing annual overheads of $26,500.

Given the above prices and returns, the profitability of the 1 ha soil culture enterprise is 11%. This return is substantially lower than the 15% level commonly accepted as the value of return required for new agricultural enterprises. However, a small increase in area has a dramatic effect on the return on capital achieved; for example a 1.25ha unit has a 19% return on investment. It is quite likely that a slightly larger soil culture system would not require significantly more input, especially of labour and land. The capital outlay for a 1ha soil culture development is $155,000.

The viability of soil-culture wasabi production is dependent on achieving a yield exceeding 8t/ha of stem material that is sold for processing at a minimum price of $9/kg.

Key contacts

Key references

Wasabi Production Guide. Prepared by the DPIF in conjunction with RIRDC September 1996 Chadwick, C.I., Lumpkin, T.A., and Elberson, L.R. 1993, `The Botany, Uses and Production of Wasabia japonica (Miq.) (Cruciferae) Matsum'. In Economic Botany, 47(2) pp.113-135

Douglas, J.A; Follet, J.M. 1992 `Initial research on the production of water-grown wasabi in the Waikato'. Proceedings of the Agronomy Society of New Zealand.

Vinning, G., 1995 Compendium of Asian Vegetables, RIRDC Research Paper No 95/12, RIRDC Canberra, pp. 309-314.

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