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.
Opuntia aciculata
Like its other cactus relatives, this deciduous and succulent species also has it leaves reduced to spines to reduce excess transpiration, which helps it to survive by conserving water in the hot climate of Texas, in southwestern United States, and North Mexico. This adaptation also helps in defending itself from being consumed by any herbivores there. It has the special ability to propagate from woody or softwood stem cuttings. It can even propagate by cuttings of leaf pads at any time in the growing season, allowing the cut surface to callus over before planting. This cactus can survive healthily and produce good many flowers only if it is fully exposed to the sun. They can also tolerate temperatures from −5 to −12 °C.