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.
Crayon Shin-chan: My Moving Story! Cactus Large Attack!
Shinnosuke ate the food that was passed from the Mayor and wanted to have a pee. But it was forbidden by Mayor's law to stand and pee on the roads. So, he had to go into the fields to pee. While peeing, a small killer cactus came near him. Shinnosuke peed on the cactus. To his surprise, the cactus got wrinkled and died. He wondered if pee was the weakness of the cactus. He told this thing to the Mayor, who was still busy thinking of his revitalization plan. Then they all realized that the weakness of cactus is water.