Viruses multiply only in living plant cells. These parasitic micro-organisms are spread by certain sucking insects, on tools or through handling. They seldom cause serious problems with house plants. They cause root and stem rots, wilts, leaf spots and galls on the different plant parts. To reduce the chances of bacterial infection, soil sterilization and good cultural practices are essential.
Nematodes are microscopic pests that burrow into root tissue or foliage.
Root nematodes may cause lesions, swellings or galls to appear on the roots. Infected plants become stunted and unthrifty, and are prone to wilting. When repotting plants, always check for signs of root nematode disease. Some species cause dark brown markings on the upperside of leaves, and small brown spots and water-soaked margins on the undersides of leaves. Nematode diseases are extremely rare in house plants, and again can be identified only through laboratory diagnosis.