There are a number of viruses that affect tobacco, and most also can infect or be transmitted from other members of the solanaciae family (potatoes, tomatoes, eggplant, peppers).
Details of the pathophysiology of these virus infections are not particularly useful for the home grower. In this discussion of tobacco etch virus (TEV), I will focus on:
Initially, the etching tends to occur along the veins.
Here, you can appreciate the fine, curlycue etching pattern. Affected areas are lighter in color.
You can see the tiny necrotic areas that eventually become holes.
Where does it come from?
In the typical home tobacco garden, a TEV infection is likely to come from nursery plants (yours or your neighbors') that are already infected. These can include, among others, tomatoes, potatoes, eggplant and peppers of every variety. Visible symptoms appear about a week after infection.
How does it spread?
TEV is carried to your tobacco by flying aphids (rather than by those that colonize a plant later on). It would seem that an insecticide might prevent such transmission, but studies have shown that transmission occurs within seconds of the flying aphid landing on the plant, and that preventive insecticide use had little impact on initial infection or on subsequent spread.
How big a problem is it?
TEV will not infect humans. If you are growing cigar wrapper, then TEV can damage the integrity of the leaf enough for it to be useless as a wrapper or binder. For cigar filler, or for cigarettes, cut tobacco and other uses, the major impact of TEV is reduced quality and productivity. A significant issue is that leaves with many tiny holes, whether from TEV or flea beetles, tend to be difficult to color cure. Very young transplants may be killed. (For fruiting plants, such as tomatoes, potatoes, eggplant and peppers, TEV can cause deformed fruit and rotted tubers.)
What should I do about it?
If you run a Google search on "tobacco etch virus management," you will find little of any value. Agricultural Extension Services tend to simply recommend planting resistant varieties (of which there are few).
I have a single plant (Wisconsin Seedleaf, shown in the photos above) that appears to have tobacco etch virus. It is fairly full, and about 2.5' high. None of the surrounding plants appear to be affected. My temptation was to allow it to grow, to see how it progressed, and whether or not it spread. I understood that it was spread by aphids, even though I haven't seen a single aphid yet this year.
I asked BigBonner, and this was his reply:
Bob
UPDATE 9 MAY 2017:
TEV seems to require active transmission by an insect carrier, and the virus does not seem to overwinter in the ground, or pass from an infected plant to its neighbors.
Once a plant is infected, there is nothing much you can do for that plant. But it does not seem to spread from the infected plant to neighboring plants, even if you allow the infected one to continue growing there.
So, if you have a couple of hundred plants going, I would be inclined to pull up the two infected plants, roots and all, and destroy them--just for peace of mind. But if you have only a small crop, I would just let them grow, and not worry about it. The thoughtless flying insects have already committed their deed. The leaf may never amount to much, or it may be smokable. People can't catch TEV.
Details of the pathophysiology of these virus infections are not particularly useful for the home grower. In this discussion of tobacco etch virus (TEV), I will focus on:
- what does it look like?
- where does it come from?
- how does it spread?
- how big a problem is it?
- what should I do about it?
Initially, the etching tends to occur along the veins.
Here, you can appreciate the fine, curlycue etching pattern. Affected areas are lighter in color.
You can see the tiny necrotic areas that eventually become holes.
Where does it come from?
In the typical home tobacco garden, a TEV infection is likely to come from nursery plants (yours or your neighbors') that are already infected. These can include, among others, tomatoes, potatoes, eggplant and peppers of every variety. Visible symptoms appear about a week after infection.
How does it spread?
TEV is carried to your tobacco by flying aphids (rather than by those that colonize a plant later on). It would seem that an insecticide might prevent such transmission, but studies have shown that transmission occurs within seconds of the flying aphid landing on the plant, and that preventive insecticide use had little impact on initial infection or on subsequent spread.
UC Pest Management Guidelines. Tomato Mosaic Diseases Caused by Potyviruses said:Pathogen: Tobacco etch virus and Potato Y virus in the potyvirus group
The tomato potyviruses are transmitted plant-to-plant by many species of aphids. Aphids only retain the ability to transmit these viruses for very short periods of time (minutes to a few hours). Thus, spread is often very rapid and localized. In general, spread of tomato potyviruses in the field occurs when aphid activity in fields is high. The type of aphid activity that promotes virus spread occurs when aphids actively move through the crop, not when they colonize plants.
http://www.ipm.ucdavis.edu/PMG/r783102611.html
McDonald SA:Epidemiology said:...secondary spread within the field was significant in the epidemiology of this virus.
...Scotch Bonnet plants can become infected with TEV for about one week before developing symptoms.
An older infected pepper field located about 80 m to the left of this field was likely to have been the original source of the virus.
[Toward the end of the growing season] the proportion of TEV infected plants ranged from 20 to 60%.
http://scholar.lib.vt.edu/theses/available/etd-03212001-144228/unrestricted/CHAPTER_3.pdf
How big a problem is it?
TEV will not infect humans. If you are growing cigar wrapper, then TEV can damage the integrity of the leaf enough for it to be useless as a wrapper or binder. For cigar filler, or for cigarettes, cut tobacco and other uses, the major impact of TEV is reduced quality and productivity. A significant issue is that leaves with many tiny holes, whether from TEV or flea beetles, tend to be difficult to color cure. Very young transplants may be killed. (For fruiting plants, such as tomatoes, potatoes, eggplant and peppers, TEV can cause deformed fruit and rotted tubers.)
What should I do about it?
If you run a Google search on "tobacco etch virus management," you will find little of any value. Agricultural Extension Services tend to simply recommend planting resistant varieties (of which there are few).
I have a single plant (Wisconsin Seedleaf, shown in the photos above) that appears to have tobacco etch virus. It is fairly full, and about 2.5' high. None of the surrounding plants appear to be affected. My temptation was to allow it to grow, to see how it progressed, and whether or not it spread. I understood that it was spread by aphids, even though I haven't seen a single aphid yet this year.
I asked BigBonner, and this was his reply:
I promptly went out and lopped off the affected plant at the ground, then removed the root ball, dirt and all. Since the latent period seems to be about 1 week, I'll know in one week if I have other plants with TEV.BigBonner said:I personally would remove it from other tobacco plants . I would also get rid of the soil and tray it was grown in .
Take a good look at any plants you may have bought from stores to see if they have the TEV . I believe it had to come from somewhere and did not come from the seeds .Maybe a neighbor who bought tomato plants .
I know of farmers here who get these types of viruses and disease in their float trays . Like root rot , the only way to get rid of it is to buy new float trays . It can be cured with Terramaster to make new root growth .But to prevent any disease from making your soil a breeding ground I would destroy it first .
Black shank is one that stays in the soil and needs tobacco to live on .
I remember back 30 years ago that farmers called what I think is TEV , rust .
As far as spreading , I'm not sure , I just know I wouldn't take a chance on it making my crop ground a new home . From what I have read It also over winters .
The TEV plants I have seen in a few fields here did not spread . I don't know why but I never seem to have any disease problems except back in the early 90's we had blue mold so bad . ....
I believe I would remove the plant and count my loss . In the long run it may be a big gain . No hole in the cigar leaf would be the gain .
Here is a link to RJ tobacco diseases http://www.invasive.org/browse/autimages.cfm?aut=2887
Bob
UPDATE 9 MAY 2017:
TEV seems to require active transmission by an insect carrier, and the virus does not seem to overwinter in the ground, or pass from an infected plant to its neighbors.
Once a plant is infected, there is nothing much you can do for that plant. But it does not seem to spread from the infected plant to neighboring plants, even if you allow the infected one to continue growing there.
So, if you have a couple of hundred plants going, I would be inclined to pull up the two infected plants, roots and all, and destroy them--just for peace of mind. But if you have only a small crop, I would just let them grow, and not worry about it. The thoughtless flying insects have already committed their deed. The leaf may never amount to much, or it may be smokable. People can't catch TEV.
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