Introduction

Rhus or wax tree (Toxicodendron succedaneum, previously Rhus succedanea) is a dangerous, allergy-causing tree that has become a weed in the Sydney region. It belongs to the plant family Anacardiaceae.

Over the years rhus has been planted in Australian gardens because of its beautiful autumn foliage. However, it is now known that contact with the tree causes dangerous allergic reactions in many people.

New trees should not be planted, and established trees should be removed and replaced with others such as Chinese pistachio (Pistacia chinensis) which has a very similar appearance.

Noxious plant

Rhus is a declared noxious plant (Noxious Weeds Act 1993) in all areas of New South Wales, and must be controlled. Local government councils are responsible under the Act for seeing that the noxious plant provisions are enforced.

The responsibility for control of noxious plants on private land rests with the owner or occupier of the land. Failure to control noxious plants could result in a notice being served, and court action. Fines may result. Alternatively, the council may enter the land and eradicate the plants themselves, charging the cost to the landholder.

The weed problem

Rhus became a serious weed problem in Sydney during the 1980s. Scattered plants still occur in many environments. Birds which eat rhus fruit spread the seed in their droppings, and since rhus grows well in almost any reasonably fertile soil, many thousands of seedlings have flourished in home gardens, in public areas and in urban bushland. Fortunately, declaration as a noxious weed and public education has brought about considerable reduction in rhus trees in all the above areas.

Rhus can be spread by movement of garden soil containing seed and as seed remains viable for many years, care should be taken when using soil previously associated with a rhus tree.

For many years rhus has been sold as a garden plant. However, nurseries are no longer permitted to offer it for sale.

Causes and symptoms of allergy

Rhus can cause painful allergic reactions. Between 12 hours and 7 days after contact, rhus causes severe dermatitis beginning with a rash, redness, itching and blisters where the skin has touched the plant. The rash is often accompanied by localised swelling of the face, arms and legs. These symptoms usually last 7 to 10 days. Chronic sufferers may have more extreme symptoms over a longer period of time. Some cases have required hospitalisation.

The sap causes the worst reaction. However, contact with any part of the tree can result in the development of some symptoms.

The allergic reaction is caused by a phenolic oily resin named toxicodendrol which has a complex active principle—urushiol. This resin will last for up to a year on shoes or other items.

The first contact with rhus usually does not produce a significant reaction. It is a subsequent contact that results in the allergy. Almost everyone is potentially allergic to rhus, and if rhus trees increase in number, more and more people will develop allergic reactions to them. Tree surgeons or yard maintenance workers should not assume they are immune because they have not reacted to initial contact with the tree. Continued contact over time could eventually result in sensitisation and in future reactions whenever contact occurs.

Description

The tree

Rhus is a native of China and Japan and neighbouring areas. It is a small, deciduous tree up to 8 m tall. It grows vigorously in its early years and later, if unpruned, forms a spreading crown on a single erect trunk.

Leaves

The compound leaves are 20–35 cm long and are divided into 9 to 15 (mostly 11) leaflets arranged in pairs. The leaflets are 4–10 cm long and 2–3 cm wide. They are bright green above and often greyish beneath because of a waxy bloom on the surface. In autumn they change to a brilliant scarlet and crimson before they fall.

Flowers

The small creamy-white flowers occur among the new leaves in spring and early summer.

Fruit

The fruit when ripe is pale brown and papery in appearance and hangs on the tree through autumn and winter.

Differences between pistachio and rhus

Although rhus and pistachio are similar, they can readily be distinguished from each other. Pistachio (Pistacia chinensis) can grow taller (to about 10 m) than rhus but has a less spreading crown. Pistachio comes into autumn colour later and less intensely than rhus. The leaflets at the tip of the pistachio leaf are usually paired whereas rhus leaves usually have only a single leaflet at the tip (see the drawings below).  Rhus leaves droop more than pistachio and the leaflets tend to fold along the main vein. Pistachio leaflets are flatter.

Control

Mechanical

Rhus should be removed with extreme caution. Contact with the sap is especially dangerous. The risk of contact may be reduced by waiting until after the leaves have fallen before attempting to remove the plant. Wear clothes which cover up as much skin as possible.

Wear gloves and work carefully. Dig up as much of the main root system as possible to discourage suckering. Do not burn any part of the plant. Dispose of all rhus debris properly by taking it to the local garbage tip. Be careful not to drop leaves and branches along the way. Rhus branches should not be mulched or chipped for garden use, as the toxic resin remains active for many months, even after weathering.

Chemical

Refer to the Noxious and Environmental Weed Control Handbook for current information.