Tobacco mosaic virus ( ToMV ) is the most prolific fungal disease that attacks tomato plants. ToMV does not limit itself to tomato plants only, but also attacks a variety of other garden plants and flowers, but garden tomatoes are the number one host plant for the disease. The virus does not pose any health threat to humans or animals, but ToMV will destroy an entire crop of tomatoes if left unchecked.
The plant disease caused by tobacco mosaic virus is found worldwide. The virus is known to infect more than 150 types of herbaceous, dicotyledonous plants including tomatoes, other vegetables, flowers, and weeds. Infection by tobacco mosaic virus causes serious losses on several crops including tomatoes, peppers, and many ornamentals. Tobacco mosaic virus is one of the most common causes of virus diseases of tomato plants worldwide.
In tomatoes, the foliage shows mosaic (mottled) areas with alternating yellowish and dark green areas. Leaves are sometimes fern-like in appearance and sharply pointed. Infections of young plants reduce fruit set and occasionally cause blemishes and distortions of the fruit. The dark green areas of the mottle often appear thicker and somewhat elevated giving the leaves a blister-like appearance. Many times the entire plant is dwarfed and flowers are discolored. Symptoms can be influenced by temperature, light conditions, nutritional factors, and water stress.
The leaves of tomato plants will begin to have yellow mottling. The newest plant foliage will be the first to show signs of yellow mottling as the young, tender growth of the tomato plant is the most susceptible. Plant leaves may have blister like lesions and/or become fern-like in appearance , and as the tobacco mosaic virus continues to spread, the edges of the plant leaves will begin to crinkle. As ToMV continues to advance in the plant, the blossoms will become discolored, fruit production will be stunted and the few tomatoes produced by the diseased plant will be misshapen and blemished.
ToMV enters a tomato plant (or any other plant) by physical contact, which can come from a human or an insect . When a tomato plant is handled (normal planting, transplanting or harvesting type handling) or an insect makes a meal from the tomato plant, an open wound occurs on the plant's leaves or stem. If the person coming into contact with a wounded plant has used tobacco in any form (chewed, dipped or smoked) and not washed their hands prior to plant contact, the residual tobacco on the hands will enter into the plant's wound and cause the tobacco mosaic virus. Insects which have recently visited a tobacco patch or discarded cigarette will also pass the ToMV disease into the plant when it bites into the plant.
ToMV can also be transmitted to tomato plants via soil absorption. If discarded cigarettes, cigars, pipe tobacco, chewing tobacco or any other form of tobacco are in the garden soil where tomatoes are planted, the plants will absorb the tobacco and become infected with ToMV.
If you use tobacco, wash hands thoroughly before touching tomato plants and never smoke or chew around the plants.
Don't place diseased tomato plants on compost pile or lay them anywhere near other tomato plants. ToMV has been shown to remain in dead plants for fifty years and could easily be spread through insects.
Rake soil to remove all diseased debris and discard carefully. Place plastic on top of the soil and allow soil to lie fallow and 'cook' under the sun for several months to kill the tobacco mosaic virus which may be lurking in the soil.
Unlike fungicidal chemicals used to control fungal diseases, to date there are no efficient chemical treatments that protect plant parts from virus infection. Additionally, there are no known chemical treatments used under field conditions that eliminate viral infections from plant tissues once they do occur. Practically speaking, plants infected by viruses remain so. Thus, control of tobacco mosaic virus is primarily focused on reducing and eliminating sources of the virus and limiting the spread by insects. Tobacco mosaic virus is the most persistent plant virus known. It has been known to survive up to 50 years in dried plant parts. Therefore, sanitation is the single most important practice in controlling tobacco mosaic virus.
Control for seedling growers and gardeners
The most common method of transferring the virus from plant to plant is on contaminated hands and tools. Workers who transplant seedlings should refrain from smoking during transplanting and wash their hands frequently and thoroughly with soap and water. Tools used in transplanting can be placed in boiling water for 5 minutes and then washed with a strong soap or detergent solution. Dipping tools in household bleach is not effective for virus decontamination. Any seedlings that appear to have mosaic symptoms or are stunted and distorted should be removed and destroyed. After removing diseased plants, never handle healthy plants without washing hands and decontaminating tools used to remove diseased plants.
Persons purchasing small tomato plants for transplanting should beware of any plants showing mottling, dwarfing, or stunting. Avoid the purchase of any affected plant. Gardeners are advised to follow the same procedures recommended for greenhouse workers when handling tomato transplants. Other control methods for home gardeners include roguing (removal of diseased plants), destruction of diseased and infected plants, and control of weeds and chewing insects. When roguing and destroying mature diseased plants from the home garden, be sure to wash hands and decontaminate any tools used in the process before contacting healthy plants.
Control for commercial producers
Commercial greenhouse producers of tomatoes should follow control practices for seedling production as stated above. It is essential for commercial growers to constantly inspect and rogue diseased production plants while the plants are in the seedling stage. An experienced individual, who is familiar with the tobacco mosaic virus symptoms, should do the initial inspection.
Roguing of young production plants is recommended and should take place before workers are allowed to prune or tie up production plants. When removing diseased plants, also remove one plant on either side of the diseased one. The reason for this is that it is almost impossible to remove a diseased plant and not contaminate the healthy adjacent plants. Never attempt to transplant a healthy tomato into the soil from which a diseased plant was removed. Roots from diseased plants will remain in the soil and provide the virus inoculum for the new transplant.
As a matter of routine, soils from which production plants have been removed, following harvest, should be steam sterilized before the introduction of new seedlings. Steam sterilization can be accomplished by steam or air-steam mixtures. In the preparation of soil for steam sterilization, sift it to remove clumps and large pieces of organic matter. The total soil mixture will have to be heated to a temperature of 200° F for 40 minutes. Since high temperatures are required, steam sterilization must be done in an enclosed system. Temperatures within the steam sterilization system should be monitored by high temperature thermometers to make sure the desired temperature has been reached. Steam sterilization of soil also will eliminate fungi, insects, nematodes, and weeds from the soil. Steam sterilization also is recommended for gravel mixtures used in hydroponic operations following the same procedure described above.
Grow individual production plants in separate containers so that the soil or growing media can be removed when roguing infected production plants. Remember that the soil harbors old root tissues that may serve as inoculum when new roots are introduced. Growing production plants in separate containers is also useful for the control of root diseases caused by fungi and bacteria.
Symptoms
Cause
ToMV can also be transmitted to tomato plants via soil absorption. If discarded cigarettes, cigars, pipe tobacco, chewing tobacco or any other form of tobacco are in the garden soil where tomatoes are planted, the plants will absorb the tobacco and become infected with ToMV.
Prevention
If you use tobacco, wash hands thoroughly before touching tomato plants and never smoke or chew around the plants.
Don't place diseased tomato plants on compost pile or lay them anywhere near other tomato plants. ToMV has been shown to remain in dead plants for fifty years and could easily be spread through insects.
Rake soil to remove all diseased debris and discard carefully. Place plastic on top of the soil and allow soil to lie fallow and 'cook' under the sun for several months to kill the tobacco mosaic virus which may be lurking in the soil.
Control
The most common method of transferring the virus from plant to plant is on contaminated hands and tools. Workers who transplant seedlings should refrain from smoking during transplanting and wash their hands frequently and thoroughly with soap and water. Tools used in transplanting can be placed in boiling water for 5 minutes and then washed with a strong soap or detergent solution. Dipping tools in household bleach is not effective for virus decontamination. Any seedlings that appear to have mosaic symptoms or are stunted and distorted should be removed and destroyed. After removing diseased plants, never handle healthy plants without washing hands and decontaminating tools used to remove diseased plants.
Persons purchasing small tomato plants for transplanting should beware of any plants showing mottling, dwarfing, or stunting. Avoid the purchase of any affected plant. Gardeners are advised to follow the same procedures recommended for greenhouse workers when handling tomato transplants. Other control methods for home gardeners include roguing (removal of diseased plants), destruction of diseased and infected plants, and control of weeds and chewing insects. When roguing and destroying mature diseased plants from the home garden, be sure to wash hands and decontaminate any tools used in the process before contacting healthy plants.
Control for commercial producers
Commercial greenhouse producers of tomatoes should follow control practices for seedling production as stated above. It is essential for commercial growers to constantly inspect and rogue diseased production plants while the plants are in the seedling stage. An experienced individual, who is familiar with the tobacco mosaic virus symptoms, should do the initial inspection.
Roguing of young production plants is recommended and should take place before workers are allowed to prune or tie up production plants. When removing diseased plants, also remove one plant on either side of the diseased one. The reason for this is that it is almost impossible to remove a diseased plant and not contaminate the healthy adjacent plants. Never attempt to transplant a healthy tomato into the soil from which a diseased plant was removed. Roots from diseased plants will remain in the soil and provide the virus inoculum for the new transplant.
As a matter of routine, soils from which production plants have been removed, following harvest, should be steam sterilized before the introduction of new seedlings. Steam sterilization can be accomplished by steam or air-steam mixtures. In the preparation of soil for steam sterilization, sift it to remove clumps and large pieces of organic matter. The total soil mixture will have to be heated to a temperature of 200° F for 40 minutes. Since high temperatures are required, steam sterilization must be done in an enclosed system. Temperatures within the steam sterilization system should be monitored by high temperature thermometers to make sure the desired temperature has been reached. Steam sterilization of soil also will eliminate fungi, insects, nematodes, and weeds from the soil. Steam sterilization also is recommended for gravel mixtures used in hydroponic operations following the same procedure described above.
Grow individual production plants in separate containers so that the soil or growing media can be removed when roguing infected production plants. Remember that the soil harbors old root tissues that may serve as inoculum when new roots are introduced. Growing production plants in separate containers is also useful for the control of root diseases caused by fungi and bacteria.
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