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
"Ferocactus" have very shallow root systems and are easily uprooted during flash floods. The "fishhook" spines and the armored web of spines enclosing the cactus body in many species of this genus are adaptations which allow the plant to move to more favorable locations. The seeds germinate in areas where water movement occurs or in areas where standing water accumulates for some period of time, and during flash floods, the hooked spines allow the plants to be caught on waterborne debris, uprooted and carried to areas where water tends to accumulate.