Davidson Plum

24.05.17

Davidson plum (Davidsonia spp.) are a native tree found in discrete areas of subtropical and tropical rainforests of eastern Australia. Due to its intense fruit acid and low sugar content, the fruit of the Davidson plum are unsuitable to be eaten fresh. However, it is an excellent fruit-based ingredient for making food products such as jams, sauces, condiments, drinks and yoghurt.

Overview

Davidson plum has long been a food source for Indigenous Australians and for colonial settlers since the early 1900s. It was wild harvested for many years, and the popularity of the fruit as an ingredient for a range of food products and growing market demand, has seen the establishment of commercial plantations since 1990.

There are three species of Davidsonia endemic to Australia, each with their own particular natural distribution and physical characteristics. The trees have several forms ranging from single trunked with a few branches and large compound leaves, which grow from the top part of the trunk to multi-trunk forms covered in dense foliage to the ground. The fruit of one of the southern species grows in clusters on stems that emerge from the trunk, generally below the branches, and is oval shaped and 3–6cm in diameter. The fruit of the northern species emerges from stalks at the top of the branches and is round with a much larger diameter of 6-12cm.

Typical of many native food industries, the Davidson’s plum industry faces a concurrent oversupply of niche markets and an undersupply of potential large-scale markets.

Facts and figures

Davidson plum has long been a food source for Indigenous Australians and was used by early European settlers for jams and sauces
Davidson plum is not used as a fresh fruit because of its sour taste, however it is a sought after ingredient for a wide range of sweet and savoury foods
Davidson plum has a higher anti-oxidant capacity than the Blueberry and higher levels of lutein than Avocado
Established as a seedling, the tree will bear fruit 3–4 years after planting and reach full production up to 15 years after planting
Davidson plum are predominantly sold domestically

Production status

Accurate information is not readily available for the wider native foods industry but a 2012 stocktake of the industry provides good estimates of industry characteristics, production figures and product value.

The market for Davidson plum was originally built on wild-harvested fruit but from 2013, supply was almost exclusively from plantations. The two New South Wales species of Davidson plum are listed as endangered in the wild and permits are required (but no longer issued) for wild harvest of the fruit. Permits are also required for harvest of wild Davidson plum in Queensland.

Davidson plum plantations vary in size from small-scale plantings of less than 1,000 trees, where the enterprise is a hobby or a second income, to commercial-scale plantings of over 1,000 trees. Generally, Davidson’s plums are commonly one of several native food species cultivated in the same farming business. Most growers sell their fruit fresh or frozen to food manufacturers, who in some cases are also producers of Davidson plum. A small number of producers value-add their own product or contract another business to value-add, and sell under their own label.

Throughout the 2000’s some plantings of Davidson plum were removed or not maintained commercially, due to lack of a market for the fruit or difficulties with crop management. The prospects of marketing Davidson plum are regarded as positive, supported by forecast increases in production volumes through the expansion of plantings and managing and harvesting fruit from previously mothballed plantations.

Map of current and potential growing regions

Uses

Davidson plum is traded as frozen whole fruit, deseeded halves, puree and dehydrated. It is not used as a fresh fruit because of its sour taste, however it is a popular ingredient in a wide range of foods, including jams, sauces, chutneys, cordials, ice-cream, yoghurt, wines and liqueurs. Increasingly, Davidson’s plum is being used in baked goods and by restaurants.

Research has shown that Davidson plum has high nutritional value. It has a higher anti-oxidant capacity than blueberry, higher levels of lutein than avocado and a high ratio of potassium to sodium.

A number of research projects have been conducted to understand and investigate the properties of Davidson plum, and other native foods, including, health benefits and health-enhancing compounds in native foods, physiological activities of native foods, functional properties and defining the flavours of native foods.

Production Requirements

Growing regions

Davidson’s plum production occurs in subtropical coastal regions and up to 80km inland in New South Wales and Queensland. The tropical plantations of Davidson’s plum are located on the Atherton Tableland and around the Innisfail and Mission Beach areas in northern Queensland

The New South Wales Davidson’s plum (D. jerseyana) is endemic to the extreme north east of New South Wales, and grows at an altitude from sea level to 300m. Natural populations mainly grow in sheltered positions on south and east facing slopes in riparian and rainforest areas. The species is listed as endangered and wild harvest is not permitted. It is the main species cultivated in subtropical plantations, but it is also grown on the Atherton Tablelands in northern Queensland.

The Queensland Davidson’s plum (D. pruriens), also called Ooray by some Indigenous groups, is endemic to coastal rainforests of far north Queensland, from Cardwell to Cooktown, and inland to near Atherton. It grows at altitudes from sea level to 1,000m. The species is not endangered but a permit is required for wild harvest. It is the main species cultivated in tropical Queensland, and it is also grown in plantations in New South Wales.

Soil type

All species of Davidson’s plum grow best on deep, friable soil with high levels of organic matter; however, they can be grown in a range of soil types and textures, as reflected by the natural distribution of each species.

Soil with good water holding capacity is important for cultivated Davidson’s plum, to ensure adequate soil moisture is available during critical growth stages; plantations of Davidson’s plum are often irrigated to maximise production.

A soil pH_(Ca) of around 5.2–5.5 is recommended for Davidsonia. Some sites may require liming to achieve this or additions of organic matter to buffer pH.

Climate

The climate range for cultivated Davidson’s plum has not been extensively tested beyond the natural tropical and subtropical growing range of the Davidsonia spp. However, there are examples of Davidsonia jerseyana that have been grown in suburban Melbourne where it fruits well.

Experience with cultivation has shown that young trees do not tolerate frost, but trees more than about three years old can tolerate a mild frost, at temperatures in the range of –2 to –3 °C.

An annual rainfall of 1,200–2,500mm would appear to be adequate but rainfall distribution throughout the year is as important as the annual total, to ensure adequate moisture supply at critical growth stages, especially at fruit setting.

Varieties

There are three species of Davidsonia endemic to Australia, each with their own particular natural distribution and physical characteristics.

D. jerseyana is commonly known as the New South Wales Davidson plum, ‘hairy’ Davidson plum or southern Mullumbimby plum. It is endemic to north east New South Wales and grows 6–10m tall. When ripe, the fruit has dark purple skin and soft, juicy, burgundy-coloured flesh. The fruit is covered by somewhat irritating fine hairs. This is the most widely cultivated species of Davidson’s plum in subtropical areas.
D. pruriens is known as the Queensland Davidson plum, Ooray (its traditional indigenous name by some groups), the Queensland itch tree (due to very irritating hairs that cover the tree), the Sour plum and the northern Davidson plum. It is endemic to tropical north Queensland, grows to 20m and has similar skin to New South Wales Davidson plum fruit but the flesh is paler in colour and contains more fibre. This species is cultivated in tropical and subtropical regions.
D. johnsonii is known as the Smooth-leaved Davidson plum and is endemic to north east New South Wales and south east Queensland. It is a small, hairless bushy tree, growing 10–18m tall. The tree is grown in cultivations in New South Wales

There has been no registered varieties or cultivars developed from any of the species of Davidson plum. Seed-bearing Davidsonia spp. are true to type when grown from seed and relatively easy to propagate. There have been some selections made by nurseries for improved performance and manageability.

Planting stock, usually seedlings at least 600mm tall, are available from specialist native food nurseries and from licenced growers that sell selected provenance material for fruit production and rainforest nurseries that stock the species or grow to order. Grafted selections may also be available.

Planting and crop management

The most productive plantations appear to be those grown in full sun or east-facing slopes with adequate soil fertility and irrigation. Site selection and design should also take into account the ability to effectively operate machinery and an irrigation system in the plantation. If siting cannot protect the plantation from wind, windbreaks should be considered in the plantation design.

The issue of sunburnt fruit has led to suggestions that south-facing slopes may be more appropriate or inter-planting with shade trees. However, experience suggests that sunburn can occur in relatively shaded situations, and the incidence of sunburn is associated with how quickly high temperatures and sunny conditions follow on from cooler, overcast periods. Plantations must be designed to avoid sunny conditions beneath the trees.

It is recommended that tree rows be deep ripped before planting to improve permeability of the soil profile for tree roots and water. If required, lime, organic matter (e.g. pelleted poultry manure or compost) and fertiliser are incorporated to correct pH, physical condition and nutrition, respectively.

Seedlings for planting should be selected from seed or cuttings of parent material that will maximise orchard productivity and manageability. Establishment rates are higher when older stock (greater than 600mm high) is planted. Older planting stock will require good attention to weed control, irrigation, and sun and frost protection throughout the establishment period, but this is less management than is required for smaller seedlings (less than 300mm).

It is recommended that seedlings be planted in rows 2.5–3.5m apart, allowing machinery access through the plantation, and spaced at 1–1.5m within the row. Planting trees too close together can lead to lanky plants that do not perform or fruit as heavily, especially the pruriens species. An inter-row sward should be established prior to planting if possible, to protect the soil from erosion during the planting stage and once the plantation is established.

Irrigation is recommended to ensure good productivity, which is particularly dependent on adequate moisture at flowering and fruit set in spring. As a guide, trees will require about 100L of water per week during dry periods, depending on the soil type. Soil moisture monitoring equipment, such as tensiometers, allows soil moisture characteristics to be understood better and irrigation to be managed effectively and efficiently.

Davidson’s plum may be planted with a range of other native food tree species in the same plantation, such as Lemon myrtle, Anise myrtle and Cinnamon myrtle, and sometimes Round or Finger limes, Lemon-scented tea trees, Riberries and other species. A diverse planting also offers benefits in reducing the burden of pests and diseases. A monoculture plantation will provide management efficiencies, but there may be a requirement for greater pest and disease management inputs.

Weeds, pests, and diseases

Weeds need to be controlled during seedling establishment to reduce competition for nutrients, water and sunlight. Mulching the planting row will help suppress weed growth through the establishment phase and as the tree matures. Hand weeding is required on occasions to remove rainforest trees, such as camphor laurel (a weed species), that germinate from seed spread by birds.

There is a range of pests (vertebrate and invertebrate) and diseases that have the potential to cause significant losses. The impacts of these pests on Davidson plum are described in The New Crop Industries Handbook – Native Foods, and the pests include:

flying foxes (in some areas only
rats and mice
king parrots
white cockatoos
native budworm
light brown apple moth
fruit fly.

Fruit fly, in particular, is a significant problem in northern New South Wales and may cause severe crop loss. When planted in the subtropical region, Queensland Davidson plum is less prone to fruit fly attack, and other pests and disease, than the New South Wales species because it fruits outside the times when fruit fly is most devastating.

Infrastructure Requirements

The cultivation of Davidson plum requires standard equipment for plantation maintenance such as a tractor, mower or slasher, sprayer and pruning equipment.

An irrigation system and soil moisture monitoring equipment is required if production is to be maximised.

Davidson plum is hand harvested, therefore picking bags or boxes will be required.

The equipment and infrastructure required for post-harvest management will include a wash and brush system, a stainless steel sorting table or machine to clean and grade fruit; a ripening room, cool storage, packing room, cold storage (optional) and trays for handling fruit through the storage stages.

If the product is being value-added on farm, a commercial-grade certified food-handling kitchen is required, as well as a dispatch, office and warehousing facilities for marketing.

Harvesting & Processing

The New South Wales Davidson plum is ready for harvest from November to February, and the trees are harvested once a year. The Queensland Davidson plum usually ripen from December to July. The growing period may be extending by growing the Queensland variety in New South Wales, allowing fruit to be picked most of the year.

The fruit is harvested by hand into picking bags or boxes or collected from the ground in the early morning and late afternoon, and returned to a sorting and packing facility as soon as possible, to remove field heat. If the fruit needs to be ripened and/or held over the harvest period to aggregate a larger quantity, it is held under conditions of high humidity and low temperature. If the fruit is not going to be processed or sold immediately, it is placed in cold storage at –18 °C. As a rule of thumb, about one cubic metre of space will be required to store 300kg of whole fruit.

Another processing consideration is deseeding. Hand-deseeded product is preferred by small processors of boutique or cottage-style products because it contains a high ratio of larger fruit and skin pieces, however, hand deseeding is very labour intensive and costly, to the extent that a profitable price cannot be set for the product. Machine pulping has been under development for several years, with the challenge of removing the fruit calyx but keeping larger pieces of fruit and skin pieces. The resulting product is well suited to sauces, jams, syrups and beverages and offers commercial-scale volume at a more acceptable price to buyers.

Generally, fruit is traded frozen, as whole fruit or deseeded halves, or growers value-add their own product. Growers may also sell their fruit as frozen puree or dehydrated product.

Markets & Marketing

Production volume of Davidsons plum has increased significantly over the last decade.

About 50% of growers value-add their own product producing jams, syrups, sauces and beverages for sale online, at local markets and to retail outlets across Australia. Producers of larger quantities of fruit may sell frozen whole fruit or deseeded halves, to small and large-scale food manufacturers. Davidson plum products are sold at specialty food and tourist stores, at restaurants and cafes, and at local markets. Predominantly, sales occur within the production region of the product. However sales beyond the production region and online are growing. Several manufacturers have established markets in Sydney and Melbourne, and in Europe.

Supply and demand for Davidson plum is finely balanced, and new growers are advised to have a marketing plan devised, in terms of understanding the end product they will produce, and who will buy it, before they plant trees.

As with many native food industries, the Davidson plum industry faces a concurrent oversupply of niche markets and an undersupply of potential large-scale markets. Overall, the industry believes there is excellent potential for growth, particularly through greater industry cooperation.

Risks & Regulations

Risks/challenges

There are several challenges common to all native food producers and their industry more broadly, such as annual variation in production volume, low return on raw product, and concurrent oversupply of niche markets and undersupply of potential large-scale markets.

At the field production level, growers of New South Wales Davidson plum face major crop and pest management issues including fruit fly, and king parrot attack, both of which can have a major impact on fruit quality and production volumes.

The advancement of the Davidson plum industry is challenged by a lack of industry organisation. Analysts and individuals have identified that the industry would benefit from better communication and cooperation within the industry to raise the profile of the fruit and its end uses, to grow market demand, address production difficulties, such as fruit damage from parrots, and collectively supply product to meet large orders for commercial production.

For producers in northern Queensland, the increased incidence of category five cyclones in the region, in the past decade, is an added challenge to ongoing business security.

Regulatory considerations

Wild harvest of Davidson plum requires a permit in Queensland and is no longer permitted in New South Wales.

Davidson plum is classified by Food Standards Australia New Zealand (FSANZ) as a traditional food of Australia and is included in the FSANZ nutrient tables. Certification by organisations such as Freshcare and HACCP may be required to sell product to supermarkets, major retailers and food service industries. Prospective growers should speak with potential customers to fully understand any product certification requirements. When processing any raw product and value-adding, consideration should be given to food standards regulations, as administered by FSANZ and set out in Chapter 3 of its Food Standards Code.