Mosaic Virus - Ask Extension
I have gardened for several years. Last year, for the first time, I was hit by mosaic virus on my cucumbers, beans, and passionflower vine. I removed ...
Knowledgebase
Mosaic Virus #863551
Asked April 06, 2024, 1:59 PM EDT
I have gardened for several years. Last year, for the first time, I was hit by mosaic virus on my cucumbers, beans, and passionflower vine. I removed all affected plant material and debris and threw them away (not composted). I have always been diligent about cleaning my tools between plants, and am even more so after this. This spring, I planted peas and noticed that they seem to already be affected with mosaic virus. Everything I read says that mosaic virus can persist in soil for years, so I assume that must be the case now. I am very dismayed. Is this an issue I am never going to be able to rid the garden of? Now that is is here, is it likely to always come back? Is there anything else I can do besides grow resistant seeds? What do people with this problem do? Just lose half their garden every season forever? Or does it eventually stop?
Montgomery County Maryland
Expert Response
The symptoms pictured do resemble those of a mosaic type of virus, but we can't be certain. Cold damage, for example, may manifest similarly, especially if seen on several unrelated species. (Granted, there are other viruses that can infect other hosts, and some viruses do have a wide host range, so an overlap is still possible.) Are you growing any other cool-season veggies, and if so, are any of them symptomatic?
Have you noticed any aphids on the symptomatic plants? Are there weeds near the planting site that may be harboring aphids? In the case of at least one mosaic virus in peas, aphids are the primary route of transmission and repeat infections. If aphids have not been detected, viral seed-borne contamination is a possible alternative. You can experiment and plant some seeds in a container indoors to see if virus symptoms appear (which would confirm seed transmission if they do). If they don't, something in the environment of the outdoor planting might be responsible instead that might not be viral.
Going forward, using a floating row cover (if you aren't already) or a fine insect mesh over the plants will help exclude aphids, since using an insecticide (even if organic) would require that the aphids be present and thus feeding already, which won't eliminate the risk of transmission before they succumb to treatment.
We are not aware of a risk of virus persistence in the soil, especially since plant viruses tend to require a living host to stay virulent. Transmission is through aphids or seed contamination (that is, infected seeds are purchased that way or came from infected plants if someone saved their own seed from year to year). Yes, growing resistant cultivars (when available) is a good general approach, though unfortunately not foolproof since no cultivar is perfectly immune.
We rarely see disease symptoms on passionflower vines. Could the plant(s) have been exposed to herbicide residues, either in compost or mulch applied to the planting area, or drifting on a breeze from a nearby property? (Is there a farm nearby? If so, do they grow alfalfa, which can harbor these kinds of viruses?) It's not uncommon for herbicide damage that isn't lethal to a plant can mimic the symptoms of a virus. If you grow passionflower again (or if the plant resprouts) and shows symptoms, feel free to send us photos for assessment.
Miri
Have you noticed any aphids on the symptomatic plants? Are there weeds near the planting site that may be harboring aphids? In the case of at least one mosaic virus in peas, aphids are the primary route of transmission and repeat infections. If aphids have not been detected, viral seed-borne contamination is a possible alternative. You can experiment and plant some seeds in a container indoors to see if virus symptoms appear (which would confirm seed transmission if they do). If they don't, something in the environment of the outdoor planting might be responsible instead that might not be viral.
Going forward, using a floating row cover (if you aren't already) or a fine insect mesh over the plants will help exclude aphids, since using an insecticide (even if organic) would require that the aphids be present and thus feeding already, which won't eliminate the risk of transmission before they succumb to treatment.
We are not aware of a risk of virus persistence in the soil, especially since plant viruses tend to require a living host to stay virulent. Transmission is through aphids or seed contamination (that is, infected seeds are purchased that way or came from infected plants if someone saved their own seed from year to year). Yes, growing resistant cultivars (when available) is a good general approach, though unfortunately not foolproof since no cultivar is perfectly immune.
We rarely see disease symptoms on passionflower vines. Could the plant(s) have been exposed to herbicide residues, either in compost or mulch applied to the planting area, or drifting on a breeze from a nearby property? (Is there a farm nearby? If so, do they grow alfalfa, which can harbor these kinds of viruses?) It's not uncommon for herbicide damage that isn't lethal to a plant can mimic the symptoms of a virus. If you grow passionflower again (or if the plant resprouts) and shows symptoms, feel free to send us photos for assessment.
Miri
Hi Miri,
Thanks so much for your reply. I am also growing beets in that bed and so far they look fine, but they are much further behind so hard to tell at this stage. I have favas, radishes, and alliums that look fine so far. Just transplanted out a bunch of brassicas started inside that are also fine.
We had more aphids than typical last year which I'm sure contributed to both getting it and the fairly rapid spread. I was planning on watching this year and perhaps using more trap crops like nasturtium. I use row covers a lot but have to admit sometimes it gets tricky if the bed has something that needs pollinating, so maybe I have to get more strategic about that. I also like seeing my plants and having easy access for weeding so I don't use them as much as maybe I should.
I don't think it would be the seed: these are peas seeds I've used for a few years (not saved seed from plants, just had a big packet!) and never had a problem until now. I did notice last summer that some of the creeping charlie in the yard also appeared to have something that looked like mosaic virus - not sure if that could be the vector.
That is good to know about the virus not persisting in the soil. I read that in several places online. I thought it must be that because it's been a bit too cold for most insects and I haven't seen any on the plants yet, so couldn't think where it would have come from on the peas unless the soil where the infected beans were last year.
That is also interesting to know about the passionvine. I don't know if I took photos, but it looks exactly like the leaf chlorosis patterning and curling that I saw on the cucumbers. On a robust healthy year old plant that had a lot of flowers and fruits. We do not use any herbicides and though we do have neighbors and close friends that do, this is in a far part of the yard where I would think that is very unlikely. These are new beds and we filled them with a combination of hugelkultur from a tree cut in the yard, our compost, bulk topsoil from a garden store for garden beds, and Black Kow compost that we ordered in bulk. Could it be possible one of those sources could have contributed? However, we filled 6 beds and only had a problem in one. And the cucumbers were growing in a different older bed where we have had none of these issues.
I suppose part of my worry/struggle is that I doubted myself and waited on pulling the cucs when they first got infected and I think that probably contributed to the spread to the beans. Similarly, when I pulled them out and planted a fresh crop they got infected but I was wanting beans that I left them until the passionvine right next to them seemed to get infected. I was struggling with getting some produce vs. pulling immediately to reduce spread although now I think I will lean towards the latter. My panic with the passiflora was realizing this could apparently spread to a perennial plant. I guess my main worry/question is - if this ends up infecting a more permanent plant like my passionvine or fig or perennial flowers or something does that mean I am going to face losing that expensive plant I have put years into vs. having a permanent vector in my yard. Everything I can find talks about how to prevent it but I suppose I am more in a place of figuring out how to manage it now that it is here.
Thank you again!
Megan
Manure composts sometimes contain undegraded (or not sufficiently degraded) herbicide residues, which surprisingly survive the animal's digestive system after they graze in a treated pasture and then excrete the residues in manure. The chemical(s) also survive the composting process in that situation. It would be hard to confirm that herbicide residues are present here, though what you happen to be doing already -- starting seeds and looking for suspicious symptoms -- is the typical approach. This is one reason why testing germination in a different material (like potting mix) can help confirm whether the symptoms appear to be tied to the compost or seed type. Sometimes herbicide residue impacts on a plant can mimic symptoms of viral infection.
The fact that the other crops you mention look fine so far is encouraging that this is not a virus outbreak.
The hugelkultur approach isn't backed by scientific research and could pose problems down the road as the coarse woody material that was buried decays and the soil grade sinks. Although touted as sustainable, it's not a good long-term planting structure and the natural layering of woody material would actually be the opposite (laying on the surface of the woodland floor, not buried), since the deeper you go through surface layers of plant debris, the smaller the pieces are, with the largest on top. (Not the largest on the bottom, as is done with hugelkultur mound creation.) This is more of a side note, though, since it probably doesn't have much to do with any current leaf symptoms, other than potentially causing nutrient deficiencies in plants whose roots are growing in a zone where microbes are actively decaying that woody material. Some nutrient deficiencies in foliage can look like other disease symptoms. Here too, testing germination and growth in another medium (like potting mix, or soil from another part of the yard) can help determine if the symptoms still appear or not.
One of the mottled-leaf diseases we see most often in cucumbers is not virus but downy mildew, though you can view examples of both symptoms on the linked page.
Plant viruses, despite being named for a particular plant ("tobacco mosaic virus," etc.), can often infect a wide variety of unrelated plants; not always...rose rosette disease, which is viral, tends to only affect roses. Plant viruses require a living vector (like aphids or mites) or direct contact with the other host plant in order to be transmitted, so if an insect isn't feeding on a host like the passionflower (and we rarely see insect pests on them), it's less likely it will pick up a virus from nearby vegetables. Root grafting, when intermingling roots fuse between different individual plants, might be one route of transmission, we doubt this happens often.
For now, all we can suggest is to keep monitoring the plants (especially asymptomatic ones, but even in case the symptomatic ones develop new growth that looks more normal) and try a germination experiment with some surplus seeds in another setting, such as in pots with potting soil and/or indoors. For any symptoms that appear on plants like the passionflower, you can send us photos before deciding to take the plant out, in case it does not look viral to us; we might be able to determine another reason for the abnormality.
We do not anticipate a virus on peas (etc.) infecting fig; we rarely see any pest or disease issues on fig in Maryland. Unfortunately, since plant viruses are incurable once an infection has taken place, there is no management approach except for plant removal (if virus is a confirmed or a strongly-suspected cause of the symptoms), which is why references focus on prevention techniques like pest exclusion (like with row covers / insect netting) and using resistant cultivars (when available) instead.
Miri
The fact that the other crops you mention look fine so far is encouraging that this is not a virus outbreak.
The hugelkultur approach isn't backed by scientific research and could pose problems down the road as the coarse woody material that was buried decays and the soil grade sinks. Although touted as sustainable, it's not a good long-term planting structure and the natural layering of woody material would actually be the opposite (laying on the surface of the woodland floor, not buried), since the deeper you go through surface layers of plant debris, the smaller the pieces are, with the largest on top. (Not the largest on the bottom, as is done with hugelkultur mound creation.) This is more of a side note, though, since it probably doesn't have much to do with any current leaf symptoms, other than potentially causing nutrient deficiencies in plants whose roots are growing in a zone where microbes are actively decaying that woody material. Some nutrient deficiencies in foliage can look like other disease symptoms. Here too, testing germination and growth in another medium (like potting mix, or soil from another part of the yard) can help determine if the symptoms still appear or not.
One of the mottled-leaf diseases we see most often in cucumbers is not virus but downy mildew, though you can view examples of both symptoms on the linked page.
Plant viruses, despite being named for a particular plant ("tobacco mosaic virus," etc.), can often infect a wide variety of unrelated plants; not always...rose rosette disease, which is viral, tends to only affect roses. Plant viruses require a living vector (like aphids or mites) or direct contact with the other host plant in order to be transmitted, so if an insect isn't feeding on a host like the passionflower (and we rarely see insect pests on them), it's less likely it will pick up a virus from nearby vegetables. Root grafting, when intermingling roots fuse between different individual plants, might be one route of transmission, we doubt this happens often.
For now, all we can suggest is to keep monitoring the plants (especially asymptomatic ones, but even in case the symptomatic ones develop new growth that looks more normal) and try a germination experiment with some surplus seeds in another setting, such as in pots with potting soil and/or indoors. For any symptoms that appear on plants like the passionflower, you can send us photos before deciding to take the plant out, in case it does not look viral to us; we might be able to determine another reason for the abnormality.
We do not anticipate a virus on peas (etc.) infecting fig; we rarely see any pest or disease issues on fig in Maryland. Unfortunately, since plant viruses are incurable once an infection has taken place, there is no management approach except for plant removal (if virus is a confirmed or a strongly-suspected cause of the symptoms), which is why references focus on prevention techniques like pest exclusion (like with row covers / insect netting) and using resistant cultivars (when available) instead.
Miri
