Queen of the night is a perennial succulent tree, usually 6 to 7 m tall, which normally consists of a short main stem from which numerous thick, vertical branches grow.
It does, however, sometimes occur as a multi-stemmed shrub. The stems are succulent, green and spiny. The stems are indented at irregular distances to create the impression of segments. The very young growth tips have succulent leaves on the ribs, but these soon drop so that the plant can be regarded as being leafless. The plants have a shallow but extensive root system.
In spring the plant produces large, funnel-shaped flowers consisting of a long tube that widens towards the top. The flowers are about 150 mm long and 70 to 100 mm in diameter. The scale-like leaves that cover the tube are thick and green to pink while the thinner, inner petals are white.
The flowers open at night and usually close again the next morning. On cool, cloudy days the flowers may remain open. The flowers are pollinated by bees and night-flying insects.
Its attractive shape, its large white flowers and edible fruits made it a popular ornamental plant in many gardens. It is also often planted as a hedge.
Queen of the night has been proclaimed a weed (Category 1 plant) under the Conservation of Natural Resources Act of 1983 (Act 43 of 1983), as amended in 2001.
The plant may therefore not be distributed or be allowed to spread. Owners and occupants of land are therefore obliged by law to control this plant in their gardens or on their farms.
Since the development of an exceptionally effective biological control strategy, the use of herbicides is considered unnecessary and even undesirable.
Two biocontrol agents are available against queen of the night: a sap-sucking mealybug (Hypogeococcus festerianus) and a stem-boring beetle (Alcidion cereicola).
Biocontrol may be replaced by the physical removal of the cactus (by uprooting) only where the cactus plants are small and isolated and would not sustain a population of biocontrol agents for a period sufficient to allow them to disperse onto surrounding cactus plants.
Single, isolated seedlings should be uprooted and suspended from a fork in a tree, or placed onto a rock or concrete surface, where they will be unable to set roots again. Care must be taken that no part of the plant is left lying where it can root. Pieces of the plant may not be discarded, and sent to refuse dumps.
Cactus plants growing in grassland can seriously reduce the grazing potential of the land. The dense, spiny infestations under trees prevent animals from finding shelter in the shade.
In tall grass Queen of the night seedlings often remain undetected until they are taller than the grass, and by this time the cactus could already have produced fruits. It is also difficult to eradicate the plant since it does not die easily.
Queen of the Night is in Category 1b. This category requires a coherent response and maintained gains in the control of these invaders. Measures must prevent the plant from forming seed, regenerating or re-establishing itself in any way.