Wasabi (Wasabi japonica)

How well established is this crop?

This crop is relatively new. It has been grown commercially for approximately 8-10 years. Commercial returns, current growers and some level of regional based research may be available to help those new to this industry.

Background

Wasabi is a native of Japan, where it grows in the mountains alongside streams. It is a member of the Brassica family and a close relative of mustard. Wasabi is used as a hot condiment to many traditional Japanese dishes including sushi and sashimi.

In a cropping situation it is traditionally grown in gravel beds with trees overhanging to give shade. Water flows through the gravel beds creating a hydroponic growing system. The key with this is to provide the plant roots with plenty of oxygen. Wasabi is not a bog plant and does not like wet feet.

In New Zealand some growers are mimicking this growing system while others are growing Wasabi straight in the soil. This is producing a grade more suitable for processing than fresh sales; however the economics may be better.

Climate

Wasabi likes an even temperature without large diurnal (day/night) variation. Once the temperature reaches 20-25C the plant wilts and will not become turgid again for several hours after the temperature drops. This seems to be because of the large leaf area in relation to the root mass. Roots simply cannot absorb water at a faster rate than it is lost from the leaves.

Winter Chilling and Frosts

Wasabi grows best in cooler climates. Winter frosts in coastal Otago (max -8C) do not affect the crop when it has its winter foliage. However a late frost in the spring when the plant is actively growing can burn off many leaves leaving the plant damaged and with the potential for fungal infection.

Rainfall and Irrigation

For soil/media grwon wasabi, care needs to be taken with irrigation due to the plants susceptibility to the Phoma disease. However, they also do not like drying out. T-tape irrigation set-ups would be better than overhead sprinklers.

Wind

Even though Wasabi is a low growing plant shelter from the wind is advisable. It will reduce the amount of damage to the plants and subsequent disease problems.

Soil

The key physical requirement of the soil for Wasabi growing is a well aerated free draining root zone. This will ensure the roots and crown are not always wet which can lead to fungal diseases.

Fertility

Wasabi grows naturally in the mountains alongside streams. These areas tend to be leached of nutrients. Soil and foliage tests, followed by expert analysis of the results is the best way to use fertilisers on this crop.

Weed Control

Wasabi is grown in the ground for up to 18 months before it is harvested. Perennial weeds such as white clover and thistles should be controlled before planting. After planting, herbicides can be used between rows with hand weeding best used between plants. Great care needs to be consisdered if using herbicides.

Varieties

Crop and Food Research has a number of named varieties of Wasabi.

Pests and Diseases

Wasabi is a brassica and suffers from the same pest and disease problems affecting all brassicas. The most common insect pests are white butterfly and diamond back moth. Both of these can be controlled with insecticides.

Phoma is the major fungal disease affecting the crop. Phoma infection leads to blackened vascular tissues on the inside of the rhizome and stems making the product un-saleable.

Layout

Plants need to be spaced approximately 30-40cm apart within a row. Beds 2-3 plants wide can be planted. Access is needed down each side of the rows for harvesting and weed control. Rows can be as long as is practical and shade is preferred.

General Management

Under adverse soil conditions and high temperatures the plants wilt rapidly making them susceptible to fungal invasion. Keeping the root zone moist but not wet requires free draining soil and then raised beds on top of this. Irrigation is also needed. The plants seem to benefit from regular applications of fungicides so scouting for observable damage weekly is advised. However, under good management in the right location Wasabi growing should be successful.

Harvest

Because most Wasabi blocks to date have been small, digging the plants by hand has been the usual method of harvesting. Some people have also experimented with small onion harvestors which have worked reasonably well. Soil is then shaken from the roots, which are washed before processing. This usually means grinding the plant material into a paste for sale or exporting rhizomes fresh to the Japanese market. The export market has been hard to service and now most producers have gone back to processing into paste for sale.

Equipment

Most of the work on current plantings of Wasabi is done by hand. A tractor will be needed to form the raised beds but after that most of the work can be done with common gardening tools such as hoes and a knapsack sprayer. At harvest you will need bins to put the harvested plants into and chillers to rapidly cool them before processing.

Returns

Wasabi has been grown successfully in a number of locations in the South Island over the past few years but only a few of the original growers are still in existence. The main problem with the crop was at the marketing end. Growers still in the business are all processing their own product into the end use and selling direct.

Returns around $12/kg for rhizome and $5/kg for the leaf matter for new growers selling to these growers/processors, have been achieved.

Contacts

Trevor Wright has experience with this crop in Otago. He can be contacted through the Dunedin Rural Development Agency 03 489 0040 or on his cellphone 021 (HORTUS)

Crops for Southland can help with some names of southern based growers www.cropsfrosouthland.co.nz

To contact Crop and Food Research for plant material look on their website www.crop.cri.nz