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.
Pereskiopsis
The shape of "Pereskiopsis" is not that of a typical cactus, it has large green leaves and grows like a bush. Only the presence of areoles, usually with spines and glochids, and the flowers, allow it to be identified as a cactus. Flowers open during the day. "Pereskiopsis" is often used as a grafting stock for other cacti, as it promotes quick growth of the scion. Its small diameter makes it an excellent grafting stock for small seedlings, but many species will outgrow the stock and need to be re-grafted or rooted. "Pereskiopsis" are tropical cactus and can not withstand any frost. Maintain a temperature of approximately 12 °C during winter and be careful with water. The stem tends to rot very easily, especially with low temperatures when the plant is not actively growing.