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.
Phytophthora megasperma
Water moulds in the "P. megasperma" complex can be found on a multitude of host plants, including many agricultural crops. It has been noted on soybeans, kiwifruit ("Actinidia deliciosa"), horse chestnut ("Aesculus hippocastanum"), hollyhock ("Alcea rosea"), asparagus ("Asparagus officinalis"), "Brassica oleracea", crops such as cabbage, cauliflower, safflower ("Carthamus tinctorius"), Port Orford cedar ("Chamaecyparis lawsoniana"), chickpea ("Cicer arietinum"), carrot ("Daucus carota"), carnation ("Dianthus caryophyllus"), eucalyptus ("Eucalyptus" spp.), walnut ("Juglans regia"), apple ("Malus domestica"), pines ("Pinus" spp.), stone fruit such as apricot, cherry, plum, and peach, Douglas fir ("Pseudotsuga menziesii"), sugarcane ("Saccharum officinarum"), and potato ("Solanum tuberosum").