Queen of the night cactus (Cereus jamacaru, C. hildmannianus, C. hexagonus) (Cactaceae)
The weed
What is known in South Africa as queen of the night cactus is probably not a single species, but a complex of various closely-related species and subspecies that are difficult to distinguish, including Cereus jamacaru, C. hildmannianus and C. hexagonus. The group is often referred to as the Cereus hexagonus complex , which is indigenous to South America and the Caribbean.
Queen of the night cactus is a very tall tree (approximately 10-15 m) with erect, columnar stems, often with a short trunk. The stems have 6-8 prominent ribs, and areoles with groups of long (1-5 cm), yellow, brown or black spines are situated on the ridges. The fragrant, nocturnal flowers are large and funnel-shaped, the inner floral parts being white and the outer ones greenish, sometimes tinged crimson or brownish. The floral tube is smooth and spineless. The flowers give rise to large (4 cm or more across), egg-shaped, crimson to pinkish red (seldom yellow or orange) fruit that split open along 1-3 slits to reveal white pulp dotted with small, black seeds. The delicious fruit attract birds, which are the most important means of dispersal for the seeds.
This species complex is cultivated as ornamentals and living hedges. A cristate, monstrosus form is also popular amongst gardeners. Bird-dispersed seeds have resulted in the spread of the cactus into the savanna of the warmer and arid parts of South Africa, where it reduces the carrying capacity of land by preventing livestock and game to shelter under shade trees during the hottest parts of the day.
Control
Cereus jamacaru has been declared a category 1b species in terms of the Alien
and Invasive Species Regulations (AIS), National Environmental Management:
Biodiversity Act (Act No 10 of 2004), which necessitates its control, or removal and destruction if possible. No trade or planting is allowed. Although herbicides exist that can exert effective control, they are not environmentally friendly, and biological control is regarded as the preferred control option. Two insect species that were initially introduced for the biological control of harrisia cactus (Harrisia martinii) are equally effective in controlling queen of the night cactus. They are a mealybug Hypogeococcus festerianus (some taxonomists regard it as H. pungens) and a stem-boring cerambycid beetle Nealcidion cereicola.
More information
The biological control of queen of the night cactus was discussed in a review published during 2011. 
pdf
The following leaflets can be downloaded:
Detailed information on the mealybug Hypogeococcus festerianus pdf
Detailed information on the stem-boring beetle Nealcidion cereicola pdf
A control strategy for queen of the night cactus pdf
Detailed information on queen of the night cactus pdf
