Irises forum: Mosaic Virus in Irises

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Name: Alastair
Maryland (Zone 7a)
FullyWashable
Apr 26, 2019 10:35 AM CST
I planted my first irises last summer. After waiting anxiously for more than half a year to see my first blooms, I'm heartbroken this spring to find that everything I planted has foliage mottling that looks to me like a mosaic virus. But everything seems to be blooming normally, and I hate to rip it all out if I don't have to, so I figured I should see what the experts here have to say, in the off chance that it's not a virus. Is there anything else that could cause these symptoms?




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[Last edited by FullyWashable - Apr 26, 2019 10:39 AM (+)]
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Name: Richard or Shawn
Joshua Tree (Zone 9a)
Birds Irises Ponds Orchids
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creativeclover
Apr 26, 2019 1:54 PM CST
What is mosaic virus?
Name: Robin
Melbourne, Australia (Zone 10b)
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Totally_Amazing
Apr 26, 2019 5:32 PM CST
Welcome! Alastair,
I can see tiny bugs on the foliage in some of your photos. I think they are aphids. These bugs are probably causing the streaks on your foliage. I think your irises are fine and all you need to do is to get rid of the bugs by squishing them or spraying your irises with an insecticide.
Name: Joshua
Melbourne, Victoria, Australia (Zone 10b)
Köppen Climate Zone Cfb
Region: Australia Bookworm Cat Lover Lilies Orchids Irises
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Australis
Apr 26, 2019 7:38 PM CST

Plants Admin

I agree I'd start with pest control and seeing if the new growth shows any symptoms after that.
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Name: daphne
san diego county, ca (Zone 10a)
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shizen
Apr 26, 2019 8:30 PM CST
Welcome! to the iris forum alastair.
(Zone 9b)
Region: California
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UndertheSun
Apr 26, 2019 9:16 PM CST
Welcome! Alastair!
Name: Monty Riggles
Henry County, Virginia (Zone 7a)
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UndyingLight
Apr 26, 2019 9:20 PM CST
Welcome!
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Name: Arlyn
Whiteside County, Illinois (Zone 5a)
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crowrita1
Apr 27, 2019 7:28 AM CST
Welcome! ….I agree on the "pest control", and also *think* I see a bit of "leaf spot'...just starting....on a couple of the leaves, so, maybe an application of a broad spectrum fungicide might be a 'good thing" Shrug!
Name: Evelyn
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evelyninthegarden
Apr 27, 2019 10:56 AM CST
Alastair ~ Welcome! to the Iris Forum!

Good luck with the leaves...after the insecticide and fungicide, wait a while and see if the problem clears up on the new leaves. Crossing Fingers!
"Luck favors the prepared mind." - Thomas Jefferson
Name: Alastair
Maryland (Zone 7a)
FullyWashable
Jun 16, 2019 4:56 PM CST
Back with an update. This IS indeed a mosaic virus. I thought it would be helpful to come back and let other people know, so they have pictures for reference, and also to tell folks here what I have learned about the viruses that infect iris. SO there is a very long post below, if you are interested.

I had a hard time believing this was due to aphid damage, as the aphids in the picture were the very first ones I had seen in the garden this spring. We had no fungal signs, so that was not on the table. It kept bothering me, so I emailed the grower as well to inquire if they recognized the symptoms and had any problems with viral infection in their nursery, and I'm afraid their response demonstrated total ignorance of viral infection in iris. They did not know the difference between a virus and a fungus. They told me it was too hot and dry for viruses where they were and advised me to try a fungicide. Thsi response was what prompted me to test the plants after all--if the grower was unaware that viral infection was even possible, that seemed a very bad sign. After obsessively reading scientific literature on plant viruses, I eventually I broke down, and shelled out for actual virus testing supplies.

It's a potyvirus, most likely Iris Severe Mosaic Virus (ISMV), but I didn't bother finding out for sure exactly which one. Testing is expensive, and the outcome for any viral infection is the same: destroy the plant. The only reason I would need to know the exact virus would be to know the range of other plants that might be infected, and the handful of potyviruses that infect irises all have pretty much identical host ranges. Unlike most animal viruses, plant viruses can infect many species. This particular family of viruses infect most of the spring bulbs: tulips, allium, daffodils, crocus and nerine. Tazetta daffodils are especially susceptible, and unfortunately I believe many or most of mine became infected. Testing becomes unreliable once the leaves are senescing, so I will have to wait for next spring to be sure I have eliminated everything that is carrying it.

These potyviruses are spread mostly by aphids, but possibly by other leaf sucking insects as well, such as leaf-hoppers. Its also possible to spread the virus during planting or dividing or any other such operation where you can introduce sap from one plant into another via infected tools and soil touching the wounds on broken roots and leaves.

It is easy to miss these infections! As you can see in the pictures above, the visual symptoms can be quite subtle--some varieties showed lots of mottling and mosaic--its most noticeable on the purple and yellow "What, again?" --and others only a faint amount, just a hint on some of the leaves. If it has not been so apparent on What, again I would probably not have even noticed it on the others at first. Many varieties of iris can tolerate viral infections with only very mild symptoms and continue to bloom and grow. However, infections do weaken the plant, causing stunting, fewer and smaller blooms, and more susceptibility to bacterial and fungal infections. And they can be absolutely devastating to the other types of plants they infect--my tazettas were quite ruined and pathetic. After reading quite a lot on these forums and scrutinizing foliage pictures, I suspect that some performance differences folks frequently attribute to climate -- plants that never reach their advertised height, varieties that are slow growers and bad bloomers even though other report they proliferate, mystery deaths, etc.--may in some cases be undetected viral infections. I certainly see photos of plants with lovely blooms, but clearly symptomatic foliage.

In addition to that, the viral symptoms tend to clear up at least partially in the summer, because these viruses stop replicating around 85 degrees F. However, the infection is not gone, even if the plant looks healthy again. Plants do not recover from viruses like animals. Plant viruses are all incurable. It will resume replicating in the fall. Infected plants must be destroyed to prevent infecting others. They should be thrown in the garbage or burned, not composted, as some viruses can persist in composting plant matter and soil for years. These potyviruses are relatively unstable, thankfully, and do not persist for a very long time in the soil where the plant was removed--two years at most. I plan to find and eliminate any bulb that emerges looking symptomatic next spring, and then wait an additional year before I plant anything new that could become infected.

The scientific literature shows that random testing finds that these viruses are widespread in nursery stock iris. I have been surprised to learn how little regulation there is in the US requiring virus testing by growers of ornamental plants. Mostly, growers are not obligated to test routinely for viral infections, and anything that does not look sick can be presumed healthy. Since many infected iris can continue to grow and bloom relatively normally, there is very little virus testing in iris except by the very large commercial growers, and typically only for the bulbous iris that are important to the florist trade. It's simply economically not worthwhile for growers to worry about if they are not producing the other bulbs that can be infected--and almost all the bulb trade is overseas.

So I suspect this came from the grower, but I'm not a 100% sure. I had not noticed any previous signs in my garden, and every single plant from the order was infected, about ten varieties, despite planting in two quite separate locations. I have not seen any other visible cases in my neighborhood (and I'm sure the neighbors all think I am crazy based on how I started minutely examining every clump of iris I saw in the surrounding blocks) . However, it is possible they acquired a virus here during that first fall they are planted in before I saw the signs in the spring. Its nature out there. Stuff happens. But any new iris I acquire after the garden convalescence period are going straight into pots for their first season, I can tell you that! I will get a good look at the spring foliage before they have an chance mingle with the rest of the garden--my spouse is now laughing about the naughty, dirty iris corrupting our innocent daffodils. Hilarious!

Also, side note: it is VERY hard to search this forum for information about viral infections of iris, because of all the people referring to the "iris virus" they have caught themselves! You've boggled Google with that one!

Anyway, I hope this is helpful to others, and I look forward to restarting my iris adventure in another year or two, hopefully virus free.

Name: Joshua
Melbourne, Victoria, Australia (Zone 10b)
Köppen Climate Zone Cfb
Region: Australia Bookworm Cat Lover Lilies Orchids Irises
Seed Starter Annuals Container Gardener Garden Photography Forum moderator Avid Green Pages Reviewer
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Australis
Jun 16, 2019 5:06 PM CST

Plants Admin

Alastair, thankyou for updating us with this information and I'm sorry to hear that the problem is indeed a virus. Viral infections in Irises is not something that there is much information about (especially on this forum), as opposed to other genera I grow (such as Liliums and Orchids, where there is somewhat greater awareness of viruses, although often still poor hygiene when it comes to Orchids).

Based on your experience, I will be checking to see what my testing options are here in case I ever need to get some testing done.
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The current profile image is that of Iris 'Volcanic Glow'.
Name: Joshua
Melbourne, Victoria, Australia (Zone 10b)
Köppen Climate Zone Cfb
Region: Australia Bookworm Cat Lover Lilies Orchids Irises
Seed Starter Annuals Container Gardener Garden Photography Forum moderator Avid Green Pages Reviewer
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Australis
Jun 16, 2019 8:27 PM CST

Plants Admin

Following up on this, I contacted the lab I use for virus testing my Orchids and asked if they can also check Iris. They can and were happy for me to quote the info here:

DPIPWE Tasmania said:Thanks for your enquiry. As you might know, there are a number of viruses (at least 7) that infect iris. The best place to start is with an EM screen as some of the most important ones are Potyviruses which can be detected via EM although not distinguished to species level. We also have antisera to a number of them to test by ELISA if you wanted to know more info.

A general EM screen (when not testing orchids) is $48.40. Depending on the result we can then quote further if required. Keep in mind though that some iris varieties are almost always infected with one of the potyviruses – at least that used to be the case.


So for any Australians that want to test their Irises, you can do so by contacting Peter Cross at DPIPWE in Tasmania:
https://dpipwe.tas.gov.au/bios...
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The current profile image is that of Iris 'Volcanic Glow'.
Name: Robin
Melbourne, Australia (Zone 10b)
Region: Australia Irises Garden Photography Cat Lover Seed Starter
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Totally_Amazing
Jun 17, 2019 3:17 AM CST
Thank You! so much for the detailed update Alastair.
Name: Lilli
Lundby, Denmark, EU
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IrisLilli
Jun 17, 2019 5:00 AM CST
Thank You! Good to know what to look for! I tip my hat to you.
You don't know if it will grow until you try!
Name: Arlyn
Whiteside County, Illinois (Zone 5a)
Irises Beekeeper Region: Illinois Celebrating Gardening: 2015
crowrita1
Jun 17, 2019 5:33 AM CST
Thanks for the follow -up post !!
Name: Evelyn
Sierra foothills, Northern CA (Zone 8a)
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evelyninthegarden
Jun 17, 2019 9:15 AM CST
crowrita1 said:Thanks for the follow -up post !!


I agree Thank You! The more we know about diseases of irises, the better.
"Luck favors the prepared mind." - Thomas Jefferson
Name: Joshua
Melbourne, Victoria, Australia (Zone 10b)
Köppen Climate Zone Cfb
Region: Australia Bookworm Cat Lover Lilies Orchids Irises
Seed Starter Annuals Container Gardener Garden Photography Forum moderator Avid Green Pages Reviewer
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Australis
Jun 18, 2019 4:27 AM CST

Plants Admin

I have now done a close inspection of my Iris collection and identified a number of cultivars (besides my inherited NOIDs) that I am suspicious about (one in particular I intend to get tested and fully expect to test positive based on the discussion thus far). I have a lot more thoughts and concerns regarding the possible sources of the virus, but won't say further until I have evidence to indicate whether I am right or wrong.

My research has also lead me to the worrying possibility that viruses in Irises are so wide-spread that effective control may not be practical or cost-effective for people wanting to grow a variety of Irises. Until the industry changes such that large growers regularly test their plants and an effort is made to eliminate virused stock, I fear that it will be a case of needing to closely manage pests and avoiding close plantings of other susceptible genera.

We also may need to simply select for virus-tolerant or virus-resistant cultivars; ones that show no symptoms are no guarantee of no infection, unfortunately, just that the plant tolerates the infection. If my white NOID tests positive, then I can only conclude that the other three NOIDs (lavender/mauve, yellow and russet) are simply virus-tolerant, as there is no way in their long history that they weren't exposed (and some of my earlier photos suggest possible symptoms as well, whereas the white NOID is almost certainly virused and does not perform well). In that case, it will be interesting to try selfing or crossing them to try to get virus-free seedlings that are similar to the parents, as some viruses are not transferred to the seedlings.

I have this horrible suspicion that very few, if any, of my Irises are virus-free, but I'll have to get some testing done and see. Due to the cost it is impractical to test everything, so I will concentrate on a select few.
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[Last edited by Australis - Jun 18, 2019 3:17 PM (+)]
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Name: Alastair
Maryland (Zone 7a)
FullyWashable
Jun 18, 2019 11:12 AM CST
Thank you so much for the acorn tips everyone! Very kind after I arrived with such bad news! I was so surprised to find that when I checked in today! Thank You!

Joshua, I had very much the same sinking feeling you seem to be conveying, and the same concern that control may not be possible or practical if growing many varieties. The silver lining may be that if you grow mainly iris, perhaps it is less important, since so many seem to tolerate viruses well? I'm a general perennial gardener, just throwing a few iris in with the rest of the lot, so for anything I add to the garden, I must to mind the effects on my other plants. (It does give me a lot of appreciation for the complexities of functional ecosystems!)

I tested mine with potyvirus Immunostrips from Agdia, which aren't cheap, but are a good deal less than $45 per test, about $50 for 5 tests here. There's a similar product from the European company Creative Diagnostics. Perhaps one or the other is available in Australia? I also tested for tomato spotted wilt and cucumber mosaic, which are also known to infect iris. And I tested for tobacco ringspot and tomato ringspot, because I had other reasons to believe those were present in the garden. They were negative for everything else. I didn't test every plant for everything, of course! The expense gets to be very high very quickly!

In the future, I think I may try biological testing as a cheap alternative. There are certain plants that are susceptible to very nearly every virus--quinoa is one of them, and some varieties of tobacco. You can inoculate these plants and see if they develop symptoms. It's quite slow, of course, as you have to grow a small plant and then let it develop a disease, but for things that I've had in the garden for a long time, I am not in a rush. For many viruses, the symptoms of infection will be the same, but it is not always important to determine exactly which virus. For me, the outcome is mostly going to be the same no matter what: no mercy! So I think I might get a few hundred quinoa seedlings going in the house and just systematically, obsessively check everything in the yard. Rolling on the floor laughing I honestly can't believe there are people who don't know what to do with themselves when they retire! I live for the day!

I also came to understand that the lists of viruses that infect a particular type of plant are not at all comprehensive, sadly.
And it's quite hard to find this information! I'm a medical librarian, so I was quite astonished it wasn't all organized in an up-to-date database like so much similar biomedical information. That's the difference in funding right there.
Name: Joshua
Melbourne, Victoria, Australia (Zone 10b)
Köppen Climate Zone Cfb
Region: Australia Bookworm Cat Lover Lilies Orchids Irises
Seed Starter Annuals Container Gardener Garden Photography Forum moderator Avid Green Pages Reviewer
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Australis
Jun 18, 2019 4:28 PM CST

Plants Admin

Alastair, you've nailed it on the funding point. Often it comes down to money.

I also hadn't thought of the test strips (the Agdia ones for Orchids are hard to get here and only test for two of the three main viruses, so sending samples to the lab is the better option for me). I'll have to see if there's strips available for Irises and how the cost compares to lab testing.

As for retirement, that is a long way off for me, but I, too, cannot see myself running out of things to do!
Plant Authorities: Catalogue of Life (Species) --- International Cultivar Registration Authorities (Cultivars) --- RHS Orchid Register --- RHS Lilium Register
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The current profile image is that of Iris 'Volcanic Glow'.
Name: Dirt
(Zone 5b)
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dirtdorphins
Jun 18, 2019 6:01 PM CST
Interesting!
and sad, and not terribly surprising...
I just learned of the dang Potyviruses this spring with my infected reticulated irises and, in attempting to research, came across the same problems (including the highly contagious and incurable human iris virus Hilarious! ). I also was wondering if many/most of my vendor acquired bearded irises could be viral considering symptoms I'd seen a bit of in the leaves last spring...so I was watching this year more intently, also with many more newly added irises, and again pondered the possibility that we may indeed have widespread and unacknowledged mosaic virus troubles in iris world.
I do know that my biggest nemesis for daffs is the evil narcissus bulb fly; they also wiped out my galanthus and will occasionally resort to buggering up a few of my hyacinths, too. Conversely, tulips, crocus, and allium do so well here amid infected irises that I cannot possibly ascribe any viral affliction to them...yet.

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