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.
Ferocactus wislizeni
The "fishhook" spines and the armored web of spines enclosing the cactus body are a defense against herbivory. Rarely a mature barrel cactus is found hollowed out by javelina but overall prickly pear experience much higher levels of damage from more species. Barrel cactus spines pose an extreme hazard for handling, penetrating boots and gloves. The roots are quite long but very shallow.