Foliar Nematodes in hostas - can they be controlled?

Ottawa, ON(Zone 5a)

Just starting a new thread about foliar nematodes.

This is MY history. Two years ago I had my first experience with them. I destroyed a couple of plants. Last year, a lot of rain and I had a lot of plants with foliar nematodes. I'm fussy about where my plants come from and I think the nems may have come in with a different perennial in my garden. But I had far too many plant affected to dig them up and heat treat or soak in bleach. And I even wonder how you would treat a whole garden with hot water.

What I DID do was to cut the plants off as soon as I saw signs they were affected and in the autumn, I carefully cut down ALL my hostas, cleaned them up really well and disposed of the foliage in the city yard waste rather than my own compost. I also sprayed the crown with a H2O2 mixture.

This year, I'm planning to spray with Neem oil and also use more H2O2. I don't know how I can control overhead watering when most of it comes in thunder storms, of which we've had quite a few.

Chris of the Hallson list thinks they are pretty well inevitable and so does my local hosta nursery owner who has a huge hosta garden of his own. Certainly they will proliferate as long as plant sales are common.

I DO believe they are not really IN the leaves at first, but rather in the soil. They tend to crawl up the leaves and enter them through the stomata, eat, multiply and leave the same way when the leaves are wet, moving on to the next plant downhill from where they were.

I DID a large hosta sale myself last year and most all of the plants were bare rooted and re-potted in fresh compost, VERY early in the season - often before they had unfurled. I've not heard of anyone who has had a problem with them and Irene bought several. However, I will not sell plants in the future unless I'm quite sure they are from a part of the garden that has not been affected.

This message was edited Jun 4, 2012 3:28 PM

Maine, United States(Zone 5b)

Well as you know, I share Chris' view, pretty much. I also have a few that looked suspiciously infected where they haven't been in previous years and I have no answer for that, as they are not in proximity to the other cases in my garden.

I had an idea that I never got around to trying. Since nematodes are a type of roundworm I thought I would take one of my dogs leftover heartworm pills and dissolve it in water and pour it on the plant. I have one isolated hosta in the corner with nematodes. I don't care about the hosta, but thought it was worth a try. I'm just not sure when the opportune time to try this would be. Hey, you never know!

Portsmouth, VA(Zone 8a)

You do not have to control the rain water, it already has H202 in it. Problem is that particles and pollution causes it to react before it hits the ground. So to compensate for that we spray the plants with a Hydrogen peroxide solution. This website will teach you how to mix the spray for your plants and how to make the insecticide with the sugar:

I checked all over and the ZeroTol is not used for root rot and it is mainly for commercial use against nematodes. (For Professional Use)

This is the website that gives the details about controlling nematodes and it is 90 degrees C not Fahrenheit which equals about 120 degrees, I think. If you read the long article just skip to the end and it says the same thing as the short article, the short one gives it to you in a nut shell.

Well, I wasn't feeling well today but I did learn a lot siting at my computer. I and everyone who buys Hostas should assume they might be infected. I work on prevention because I do not want any, I might have them but I don't know for sure. As the season progresses I will keep a watchful eye out for the symptoms, and clean the beds in the fall, removing all the dead leaves and stalks, they said the nematodes are in the buds but at the end of fall I never have any buds. I have heard of people cutting the buds off because they do not want any seedlings and it does not harm the plant. At the time you do all this it would all be dead anyway.

I did not mean to offend John, I just thought he was a salesman for ZeroTol.

Ottawa, Canada

Early on, when the nematode question came to my attention, I did some research about the problem and what I read seemed to indicate that nematodes are unavoidable and that the way to combat them was to increase the microbes in the soil which keep these critters in check. One means of increasing the beneficial bugs in the garden, it was suggested to provide corn meal to the soil. I'm afraid I didn't keep a record of the sites but they were state agricultural in origin.

I believe ViolaAnn was going to try the corn meal but I don't know whether she actually did.

I don't think John is a salesman for ZeroTol, otherwise he wouldn't have spelled it zeroltol. AND anyone that has been in the habit of posting in this forum would know that Virginiarose is not in the habit of offending. It's just that they have a difference of opinion on economics. I appreciate both views.

P.S. I think I would do just about anything short of bank robbery to protect my investment in hostas, not just for finances sake but also for my hostaholic emotional well-being. Hey, has anyone thought of offering hosta insurance yet? (said tongue in cheek)

This message was edited Jun 4, 2012 7:08 PM

Fairchild, WI

Thank you for starting this thread ViolaAnn.
I would be interested in the strength of the Neem oil and H2O2 that you would consider to be affective.

I do not have any experience treating a plant with foliar nematodes as I fortunately have never found a plant in my gardens with them.
That being said ... I would like to add a couple things for people to research.

I have heard and read of the use of "beneficial nematodes" to combat the "bad" nematodes. That is certainly worth looking into as they are supposed to get rid of ticks and other nasty critters as well.

The following links provided by virginiarose post above are well worth checking out:

The first link is to a post/review of the product with this reference ... "There was an article in an old Hosta Journal about ZeroTol controlling foliar nematodes about 90%." I logged into the members only section of the American Hosta Society but only found 1 reference in my search for foliar nematodes (again a persons post vs anything "scientific") and it did not shed anymore light on the subject than what is given above. The person posting did mention a chemical that is now banned that would get rid of them. I hope I can find the aticle in the Hosta Journal. Another link in the above post is to an article about foliar nematodes that is well worth reading.

It would be nice to know the strength and how much of the ZeroTol that was used. Sounds a lot easier than other methods. Except for letting the beneficial nematodes wiggle around eating the "bad" ones for us!

The H2O2 seems promising. I think the strength of the over the counter bottles is 3% - someone correct me if I'm wrong. So what strength is strong enough? Is there any research to back this up? ZeroTol (which is a type of hydrogen peroxide with a strength of 27%) has a recommended dilution of 1:100 or 1 1/4 oz per gallon when used at a "curative" strength for certain plant diseases (not nematodes - they are not mentioned in any info from the company that I'm aware of). Not sure what percent that would be. If anyone has access to the Hosta Journal article ... could you please share some info? I'm not a chemist ... but I do not think that comparing over the counter H2O2 with ZeroTol is comparing apples to apples. So I do not think it prudent or wise to substitute one for the other - unless it is an experiment.

ZeroTol is used for root rot which is caused by (among other things) members of the water mould genus Phytophthora. It is a broad spectrum algaecide/fungicide. I have not seen any reference to its use against nematodes in the link that virginiarose provided above or anywhere else. This is the link I'm referring to:
Perhaps virginiarose could point out where she found the following: "I checked all over and the ZeroTol is not used for root rot and it is mainly for commercial use against nematodes. (For Professional Use)" The professional use only is on the website but baffles me as they sell the stuff and there are no restrictions or "certifications" necessary to buy it. However, that strength is very corosive and care needs to be taken when mixing it.

irawon is correct I'm not a salesperson for ZeroTol or anyone else. Just someone who is interested in sharing info and learning new things till the day they "plant" me.

EDIT: Another thought came to me regarding the strength of whatever it is we use. Are we trying to cure a condition or prevent a condition. A curative ratio may need to be 2 to 3 times the preventative ratio. A curative ratio is usually so strong that it could injure some plants. The preventative ratio would not help if the plant needed the curative ratio. It is often recommended that a curative ratio is followed after so many days by a preventative ratio.

IMHO this means that if we do not have any scientific research to back up our approach we are probably wasting our time and money even if all we use is boiling water.

Could the use of "unproven" methods be the reason so many are finding this problem spreading?
Perhaps some of these methods even cause the spread!


This message was edited Jun 4, 2012 7:54 PM

Portsmouth, VA(Zone 8a)

Thank you irawon! I would love some Hosta Insurance but it is probably too expensive. :)

Portsmouth, VA(Zone 8a)

My links were for alternatives for ZeroTol, You mentioned it's use on the other thread. I don't think anyone knew anything about it till you mentioned it and it is too expensive for homeowners. If you have a farm or a golf course I am sure you could find use for it. I don't think anyone with crown rot or nematodes will spend that much money, the reason it comes in a 2.5 gallon jug is because they mix it in tanks for commercial use on golf courses and farms and nurseries. The original discussion was about a single plant, then turned to nematodes when you mentioned ZeroTol. Why would you bring this up for use on a single plant? You were upset because she used a little bleach?

Fairchild, WI

A single plant can be very valuable to an individual. It may be expensive. Even more important ... it could be a plant that a loved one who has passed on has given you ... cannot even put a dollar value on that!

Like I said ... I use bleach.

ZeroTol is available in 32 oz. for $23.95 at ... a link you provided!
It has the strength you need to get the job done. Has a very long shelf life.
It is not to expensive for homeowners.


This message was edited Jun 5, 2012 4:44 PM

Ottawa, Canada

Well, I've read all the literature provided by Johnny and Virginiarose and these are MY observations. Feel free to disagree as I may not have interpreted the facts correctly.

In regard to nematodes this is what I learned that is important to ME:

1. In order to spread from one area of a leaf to another, nematodes reemerge form a vein deleneated area of the leaf to the leaf's surface and require water to move from one area to another. Therefore, I would think that removal of affected leaves as soon as possible would be beneficial in preventing the spread. Detection of nematodes and the signs of their presence is, therefore, necessary.
2. Nematodes don't feed on the roots of hostas.
3. Since nematodes remain in decaying plant matter and the soil over winter, good clean-up of dead plant material in the fall (and at other times) is beneficial.

Both Virginiarose and Johnny agree on the benefits of hyrogen peroxide/dioxide (H2O2) to plant health and the possibility of its use in keeping foliar nematodes in check. It's benefit is in its contact properties, that is it has to come in contact with the nematode to be of any use in eradicating nematodes. Their divergence in opinion seems to occur in the delivery of H2O2, that is the strength of the solution and its cost. ZeroTol contains 27% hydrogen peroxide/dioxide (H2O2). Pharmaceutical grade hydrogen peroxide contains 3% H2O2. Food grade hydrogen peroxide contains 35% H2O2. Thirty-two oz. of ZerTol costs $23.95. Therefore, it remains to be determined what the cost of food grade hydrogen peroxide is and how it should be used in solution as it may be a cheaper alternative to ZeroTol. However, the other thing to consider is the shelf life of ZeroTol as opposed to food grade hydrogen peroxide. The other consideration for me here is the availability of ZeroTol in Canada.

EDIT: Neither Johnny nor Virginiarose has claimed that ZeroTol and hydrogen peroxide prevents nems. It's the sites that they have provided that lead ME to assume that its contact properties would be beneficial in controlling them.

I'd be interested to hear from ViolaAnn why and how she plans to use Neem Oil. ViolaAnn, please explain your use of "more H2O2".

Another observation: It seems to me that the use of H2O2 would be most beneficial after rain or watering because this would be when the nematodes would be on the move on the leaves' surfaces and this is when the contact properties of H2O2 would be of use.

What have I missed?

This message was edited Jun 6, 2012 12:56 PM

This message was edited Jun 6, 2012 9:00 PM

Ottawa, Canada

Noreaster, the use of veterinarian heartworm medication sounds interesting. You never know.

This message was edited Jun 6, 2012 1:00 PM

Ottawa, ON(Zone 5a)

Irene - I'm flying by the seat of my pants, but after hearing a talk at Ottawa Hort Society last year, I'm just going to try spraying the need oil. Maybe it clogs the stomata in the leaves. I don't really know.

Maine, United States(Zone 5b)

Well, I'm feeling the nematode aggravation again. This year, Maui Buttercups and Blue Mouse Ears look infected. These are side by side and have not previously shown any signs, nor have they ever been in proximity of any of the other infected ones I've had through the years. It's just so frustrating. They came from good sources, as did the one I bought last year that also looks like it has nemes. I thought it looked like it had them last year but wasn't sure, and now it seems that I was right.

And in other bad news, one of the hosta that I heat treated a few years ago looks infected again...

Royal Oak, MI(Zone 6a)

Sad to say, but I think I have a couple infected plants now =(

'Gold Regal' has a leaf that looks pretty obvious, and I just got it last month. Trying to decide if I want to treat it or just toss the plant before I get attached. It wasn't expensive, just isn't a common hosta these days. Oh well.

I got 'Golden Scepter' and 'Lemon Lime' in trade few years ago, and they're both looking infected. 'Golden Scepter' has never grown well, so I'm just gonna pitch it.

Unfortunately, GS is next to 'Golden Tiara', which has a suspicious leaf now. I do have a separate large division of it, but I hate to lose such a nicely growing plant. Sigh.

Ottawa, ON(Zone 5a)

Well, I've seen some too. This year, I'm mostly just cutting off the infected leaves. I don't really think total control is possible given that they infect many perennials - not just hostas.

Maine, United States(Zone 5b)

Yeah, I'm not gonna heat treat anything anymore as it looks like my previous attempt was not as successful as I had thought. I'm not going to throw anything out because then what- live with a bunch of holes all over the garden? My garden is too small for that, and I don't want to turn it into a sculpture garden. :/ And then I'd just be waiting around for the next hosta that has never looked infected to show signs, I guess. I wonder if they take years to build up enough of a population in a plant to start looking symptomatic, especially in the thicker leaved ones which is mostly what I have.

It just really sucks that they can't make something available to the home gardener that works on these parasites.

Austell, GA(Zone 7a)

Does anyone have a picture of what the damage looks like?

Thank you!


Maine, United States(Zone 5b)

Brenda foliar nematodes show up in late summer looking like yellowing streaks between the veins of a leaf. Eventually those yellow streaks turn brown. Here is a pic of a few of mine from past years. If you google foliar nematodes hosta you will find better pics. They are pretty distinctive

Thumbnail by Noreaster
Maine, United States(Zone 5b)

This one was interesting to me- a stray seeding a few years ago looking like it's got nematodes.

Thumbnail by Noreaster
Ottawa, ON(Zone 5a)

I've had them show up in pots that had new soil this year as well. They are in the soil. I still don't believe they actually stay in the plant over winter, but return to the plants quickly in the spring. I just cut down a few of my minis which had too many leaves affected to simply trim. And I'm about to spray all that area with water, H2O2 and soap. maybe ammonia too, as we had rain yesterday and I've actually seen slugs today. It's been so dry I've not seen many slugs, but they've still damaged some hostas.

Austell, GA(Zone 7a)

Thank you Noreaster and Ann,

Something else to worry about. I have not noticed any but I will be on the look out for this.

Maine, United States(Zone 5b)

Well, I officially throw in the towel on this! The three new hosta I bought this year (not including the ones from Hallsons) all look like they've got nemes. Then, several others not mentioned in my earlier post also look like they have them...these are all over the garden, and have been there for years. I'm just going to enjoy my spring and early summer with my plants and hope that the powers that be will come up with something we can use to erradicate them. Otherwise I'm sure my whole garden will eventually have them.

Ottawa, ON(Zone 5a)

Try cutting down all your plants in the fall to give a really good garden clean-up. And then douse the crown and area around it with a solution of H2O2 and water. It can't hurt. I DO have a few small hostas that showed signs of nems the last couple of years and so far do not this year.

Ottawa, ON(Zone 5a)

I found them yesterday in a plant IN A POT that has never been anywhere close to plants with nems. ;-(

Maine, United States(Zone 5b)

It's maddening, isn't it? I think they are truly unavoidable.

One of my infected looking ones this year is Delta Dawn. Two years ago, after the hail, DD is the hosta that I cut all the leaves off, as a test. This year, I moved it into a new pot , rinsing off all the old soil before that. And somehow it's got nemes

This message was edited Aug 12, 2012 8:44 AM

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