By Erin Marissa Russell
Tobacco etch virus is spread by aphids of 10 different species on plants in North and South America as well as Africa, Asia, Turkey, and Spain. An aphid in contact with an infected plant for as few as 10 seconds can become a carrier of tobacco etch virus, and the aphid will remain a carrier for up to four hours, having the highest potential to infect plants for the first hour. The disease primarily infects pepper plants but can also appear on tomatoes, tobacco, and weeds. In addition to aphids spreading the virus, it can also be contracted through contact with infected garden tools, infected plant stakes, and the hands of gardeners who have touched infected plants.
Identifying Tobacco Etch Virus
Tobacco etch virus is more challenging to diagnose than some plant diseases because the symptoms of the virus and their severity tend to change depending on the species of plant affected, the virus isolate at work, the age of the host plant when it was infected, and conditions in the environment. Tobacco etch virus tends to impact burley tobacco plants more severely than flue cured tobacco varieties.
Symptoms can first begin to appear between seven and 14 days after infection, or it can take as long as four weeks for the disease to become apparent. With tobacco crops, the disease is often noticed first as the plants move into the flower bud stage, and symptoms become more severe after topping. When tomato plants are infected, the crop may yield up to 25 percent fewer tomatoes due to effects of the virus.
Infected plants may show the following symptoms.
- Mottled leaf appearance
- Puckered leaf shape
- Distorted foliage shape
- Wrinkled foliage
- Stunted growth
- Mosaic-like patterns on infected fruit
- Yellowed streaks on plant leaves
- Necrotic areas on plant foliage
- Crinkled leaves on infected tomato plants
- Wilting even when water is available (Infected hot pepper plants may show this symptom, while sweet pepper plants will not.)
- Reduced yield, more pronounced with plants that were younger when infected
Preventing and Treating Tobacco Etch Virus
- Reflective mulches, such as those made from aluminum foil, can be spread around vulnerable crops to reduce their risk of contracting tobacco etch virus. The reflective mulch will deter the aphids that spread the virus from contact with the susceptible plants. Organic mulches that are not reflective, such as sawdust, corncob mulch, or wood chips, have also been effective in preventing the virus, according to some reports.
- If you are a gardener of hot or sweet peppers, you can avoid having to worry about tobacco etch virus by growing resistant varieties of peppers. Resistant varieties of other host plants are not yet available. Bell peppers tend to be naturally resistant, as do sweet yellow wax peppers and jalapeno peppers. Resistant varieties of burley tobacco are also available on the market. There are no resistant varieties of tomatoes as of yet, unfortunately.
- Clean the garden carefully at regular intervals during the growing season and again after removing the plants when harvest is done. Clear away and discard any plant debris that could potentially have come from an infected plant. Do not include potentially infected plant material in compost, as there is a risk (even with compost piles that get hot) of passing the disease along when the compost is used.
- Because invasive weed plants can serve as an alternate host for tobacco etch virus, it’s important to carefully weed both the part of the garden where vulnerable plants are growing and the area surrounding it as well. Notable alternative host plants that are invasive weeds include blue toadflax (Linaraia canadensis L.), ground cherry (Physalis spp. L.), jimson weed (Datura stramonium L.), black nightshade (Solanum nigrum L.), pigweed/lamb’s quarter/white goosefoot (Chenopodium album L.), soda apple (S. aculeatissimum Jacq.), sickle pod (Senna obtusifolia), and thistle (Cirsium). Ideally, you should have 30 yards of empty space between your crops and any invasive weed plants.
- Treating plants with a mineral oil spray has been reported effective because keeps the aphids that normally spread the disease at bay. Gardeners can purchase horticultural oils containing mineral oil to use on their plants or make their own concentrated white oil. Homemade concentrate can be made by mixing a cup of white mineral oil or vegetable oil with a quarter cup of dish soap (not containing bleach) or Murphy’s oil soap. When ready to use, mix one tablespoon of the concentrate with four cups of water, and spray to apply to plants, especially targeting the leaf undersides where aphids congregate.
- Barrier crops can be an effective way to defend vulnerable crops from coming into contact with disease-carrying aphids. You may either intersperse a trap or sacrificial crop in with the crop you wish to protect, or you can plant the barrier crop around the perimeter of the crop you wish to save. If you would like more details about using barrier crops to reduce your plants’ risk of being infected by aphids carrying tobacco etch virus, see this helpful document from the University of Hawai’i at Manoa College of Tropical Agriculture Cooperative Extension Service [https://www.ctahr.hawaii.edu/oc/freepubs/pdf/SCM-18.pdf].
- Choose the location of late settings carefully. Locate them as far away as you can from any areas where you planted tomatoes or peppers earlier in the season. Aphids that have been in contact with infected plants may be in the fields where early tomatoes or peppers grew, so you want to make it as unlikely as possible that these virus-carrying aphids will come into contact with your late settings.
- Inspect your vulnerable crops regularly for signs of disease so that you can identify diseased plants early and take action to minimize spread of tobacco etch virus. Some gardeners choose to treat infected plants with insecticide before removing them from the field so that any aphids that have been in contact with the infected plant will not be able to continue spreading the disease. You can also use the homemade white mineral oil spray we have provided the recipe for to treat infected plants before removing them.
It’s important to understand that in nature, plants with tobacco etch virus are likely to be infected with additional viruses and other plant diseases as well. If the symptoms you see in your plants seem not to fit the way any one particular virus is supposed to be identified, infection from multiple sources may be a potential cause.
In cases like this, it may be best to collect samples of your infected plants and contact your local agricultural extension office to have them tested. For the most reliable results, pull entire plants to serve as samples, and keep the sample specimen somewhere cool so it won’t lose too much moisture. The lab is better able to test fresh, living plant tissue than withered or dried-out plant tissue. You can find your local extension office by clicking the appropriate state on this map from the National Pesticide Information Center [http://npic.orst.edu/pest/countyext.htm].