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.
Pilosocereus robinii
Other threats to the species include the destruction of its habitat during development. Populations on the Upper and Lower Matecumbe Keys have been mostly eliminated due to residential development. Development also leads to habitat fragmentation. Hurricanes are a threat to the cactus because the winds can break cactus branches or bring down taller vegetation, causing injury; however, hurricane action may open the canopy, providing sunlight to the cactus, which may be beneficial. As of 2009 there are seven known populations of this plant in Florida, located on four of the Florida Keys.