Imbricate cactus (Cylindropuntia imbricata)(Cactaceae)
The weed
Imbricate cactus (Cylindropuntia imbricata), also known as devil's rope pear, occurs naturally in central and northern Mexico as well as in the southern parts of the USA.
It is a shrub, often tree-like, 1-3 m tall, with a short trunk and side branches arranged in whorls. The segments of the branches are dull grey-green, with prominent tubercles that give the branches the appearance of woven rope. Groups of long, stout, barbed spines which can be silver-grey, yellow, reddish or brown and have silver-grey to yellow sheaths, are scattered sparsely across the stems. The dark pink to magenta or purple-red flowers are open during the day, giving rise to spineless, yellow fruit, clustered at the end of the terminal segments. The fruits have distinct tubercles that are nearly equal in length. The fruits do not form long chains, but a secondary fruit develops occasionally from an older fruit. Despite having a large number of seeds, the fruit is hard and unpalatable and not eaten by man or beast, and seed dispersal is therefore not very effective.
Imbricate cactus was probably brought to South Africa for ornamental purposes but has escaped from rockeries and is now invading large areas of the Northern and Eastern Cape, Free State, North West, Gauteng and Limpopo Provinces. It is problematic mainly in pastures, where its vicious, barbed spines can seriously injure animals. The extraordinary ability of the weed to spread rapidly and completely take over a patch of land is cause for great concern. Imbricate cactus is also naturalized in Australia.
Control
Imbricate cactus was declared a category 1 weed in terms of the Alien
and Invasive Species Regulations (AIS), National Environmental Management:
Biodiversity Act (Act No 10 of 2004); consequently land users are under obligation to effectively control this species, or to remove and destroy it if possible. No trade or planting is allowed. Imbricate cactus is extremely difficult to eradicate once it has become established, due to its spiny nature and the fact that each part that breaks off the plant will give rise to a new plant. Currently no herbicides are registered to control it chemically. Integrated control, consisting of biological control plus felling, is the preferred control option in South Africa.
The cochineal insect, Dactylopius tomentosus, which was released in South Africa during 1970, is effective in killing small plants and detached segments of imbricate cactus, and will also cause the segments to drop off a large plant plant. However, the woody stems enable large cochineal-infested plants to regrow despite severe defoliation. To prevent regrowth, the old, woody cactus plants should be felled close to the ground approximately two years after establishing the cochineal on them, and all plant parts stacked to protect the cochineal from rain. This has proven very effective in controlling large imbricate cactus plants.
More information
The following fact sheets can be downloaded:
>>>Specific IAP Species and their control according to common names
>>>Specific IAP Species and their control according to botanical names
