Tomatoes are vulnerable to a number of viral pathogens, including the tobacco mosaic virus, cucumber mosaic virus and potato virus Y. No practical means exist for treating plants infected with a viral disease. Infected tomatoes are often uprooted and destroyed to prevent the outbreak from spreading to neighboring plants. Symptoms of viral infections include discolored patches or streaks on foliage, wilting of green growth and sudden death of plants. Controlling infestations of migratory sap-sucking insects, such as aphids and mites, is key to preventing the spread of these viral diseases, according to North Carolina State University.
Tomatoes are common garden vegetables that are cultivated domestically and commercially in the United States. They can be grown in outdoor gardens throughout most of North America and they can survive in most temperate climates. They are also frequently grown in greenhouses and hydroponic environments, including aquaponic systems that support fish and plants together in a controlled environment. Tomatoes grown in greenhouses and hydroponic systems are subject to the same diseases as those planted outdoors, although the frequency of some diseases is increased in outdoor environments.
Fungi in the genus Pythium are among several groups of pathogens that cause root rot disease in tomato plants. Pythium is a serious threat to tomatoes cultivated in greenhouse and hydroponic environments because it can survive in soil or water for long periods of time. Pythium decays the roots and lower stem of its host, causing discolored markings on infected areas. Pythium fungi can infiltrate greenhouses during transplants or through contaminated material, such as non-sterilized water and soil, according to the British Columbia Ministry of Agriculture. Root rots are deadly, so infected plants and their debris should be removed from a hydroponic system as soon as possible.
Tomatoes are vulnerable to several wilt diseases that are also caused by soil-borne fungi. A specialized variety of Fusarium oxysporum is a host-specific parasite of tomato plants. Fusarium wilt damages stems, leaves and fruit of tomatoes, causing discoloration of leaves and wilting of the entire plant, according to Iowa State University. Infected stem tissue turns brown and leaves shrivel before falling from the tree. This disease causes widespread damage across the entire plant and severely diminishes the plant's fruit yield. Another wilt disease, called Verticillium wilt, can also infect tomato plants. Its symptoms are similar to those of Fusarium wilt, but Verticillium does not harm its host as quickly as Fusarium.
Leaf Spot Diseases
Leaf spot diseases are a common ailment of garden plants, trees and shrubs. Tomatoes are subject to several leaf spot ailments, including the fungal Septoria leaf spot disease and bacterial spot caused by the Xanthomonas campestris pathogen. These two diseases cause brown or yellow spots on the surface of leaves. Infected tissue eventually decays and withers as the spots grow in size. The spots caused by the Septoria fungus have dark gray centers, while those caused by the bacterial pathogen do not, according to Iowa State University.
- Iowa State University: Tomato Diseases and Disorders
- University of Illinois Extension: Aquaponics Combines Fish, Tomatoes, and Ingenuity
- North Carolina State University: U.S. Greenhouse/Hothouse Hydroponic Tomato Timeline
- British Columbia Ministry of Agriculture: Management Strategies for Pythium Diseases of Greenhouse Vegetable Crops in British Columbia
- North Carolina State University: Virus Diseases of Greenhouse Tomato and Their Managment
- University of Illinois Extension: Tomato