Cactus
Fungi, bacteria and viruses attack cacti, the first two particularly when plants are over-watered. Fusarium rot can gain entry through a wound and cause rotting accompanied by red-violet mold. ""Helminosporium" rot" is caused by "Bipolaris cactivora" ( "Helminosporium cactivorum"); "Phytophthora" species also cause similar rotting in cacti. Fungicides may be of limited value in combating these diseases. Several viruses have been found in cacti, including cactus virus X. These appear to cause only limited visible symptoms, such as chlorotic (pale green) spots and mosaic effects (streaks and patches of paler color). However, in an "Agave" species, cactus virus X has been shown to reduce growth, particularly when the roots are dry. There are no treatments for virus diseases.
Bundala National Park
The seeds of the Opuntia cactuses (called Kathu Potak in Sinhala) are spread by macaque monkeys, and perhaps other animals and birds, that eat the fruits. It is also spread by people cutting down the cactus but leaving the cuttings, which then re-sprout. No biological control measures have been carried out with the moth "Cactoblastis cactorum" so far. Manual removal of the cactuses will be impossible as the area where they have spread over is vast.