Virus diseases on commercial tomatoes are not usually a major problem because growers know the precautionary measures to take to prevent them. Home gardeners can learn these as well. Cleaning up waste debris around growing plants and pest control for aphids are essential to prevent viruses from taking hold. Consult your nursery professional for pest control advice. Virus disease problems can be divided into two categories: ones spread by humans and ones spread by insects.
Tobacco mosaic virus is seed-borne and also spread by people from plant to plant. It can live up to 100 years in dried plant materials and is often present in tobacco products. Symptoms can vary with type of virus strain and plant conditions. Some of the symptoms include a light and dark green mosaic pattern on leaves. Some virus strains cause yellow mosaic patterns and leaf malformation. Tomatoes may not be infected with the mosaic patterns but the plant's tomato output is reduced in size and number.
Single and double virus streak and tomato leaf rolling are three distinct diseases which involve the tobacco mosaic virus. Brown streaks on tomato plant stems may be symptoms of single streak virus. Brown indented rings may appear on the tomatoes. The double virus streak symptoms are brown streaks on stems and irregular brown spots on the fruit. Leaf rolling disease causes leaves to curl inward tightly. It is the result of the tobacco virus interacting genetically with the "wilty gene" found in some tomato varieties.
The cucumber mosaic virus is common and is spread by aphids rather than people. The characteristic symptom is shoestring leaf blade development. Leaves look thin and do not have the recognizable tomato leaf shape. Plant infection can be temporary, with new leaves showing a mottled effect but not the shoestring blade malformation. Many effective organic controls exist for aphids, such as garlic oil spray. Introducing ladybugs into the garden also deters aphids.
Tobacco Etch Virus/Potato Virus
Both of these viruses are common in southern U.S. and Central America. Symptoms are similar to the tobacco mosaic virus with its mottled effects, leaf distortion, and severely stunted plants. The potato virus causes leaf rolling and marginal leaf discoloration. The potato virus causes leaf rolling and marginal leaf discoloration. Both viruses are transmitted by aphids, so good insect control methods are necessary.
Potato Leafroll/Spotted Wilt Virus
Potato leafroll is commonly associated with the potato plant but can also infect tomatoes. Symptoms include leaf rolling and discoloration on leaf edges. Discoloration often looks mottled or yellow. Tomato spotted wilt virus causes brown streaking on the stems and severe mottling of the fruit. Tomatoes look bumpy and misshapen. Organic pest control methods are generally successful with both virus.