Foliar Nematodes

The mention of nematodes to a hostaholic is enough to bring fear and have them start pulling out hair and plants. I was fortunate enough to receive some wonderful new varieties of Hostas in a trade on August 11th, 2007, but sadly I noticed about 3 weeks after receipt that I had more than just new plants: I also had new bugs. NEMATODES. I immediately posted some pictures on one of the hosta forums I frequent and as you can see from the postings the advice ran from destruction to treatment. One of the posters -a lady with whom I'd traded some Hostas earlier this past summer- actually had 2 suggestions, one of which rather appealed to me: she pointed me to a thread on a different forum where a chap by the name of Bruce Banyai indicated he and his late mother, Pauline Banyai, had been following a practice of using bleach to deal with nematodes. See below.

As someone who has watched the nematode hosta invasion for +35 years, I am reminded of several other notes after reading the excellent Kines summary.

Beware that your hosta are living organisms subject to environmental stress: they have natural defenses same as humans. When those defenses are suppressed or challenged the plants get weaker and opportunistic germs and Nematodes get aggressive. May be part of the seasonal explanation.

Most chemical treatments border on "killing the plant" and its pests, but if the plant has good genetic material, the pesticides kill the susceptible pests first: if the plant material is weak and dies as well, so be it.

My grandfather's Detroit area greenhouse/nursery business, started in the mid-1920's, used soil sterilization (steam) to kill soil-borne pests. They then began to use bleach when possible to limit further attacks on structures, pots and soils. This was in the era before chemical pesticides.

My mother, the late Pauline Banyai, the Michigan Hosta Lady, was often heard to say when she started dividing hosta: where is my bleach?

We would soak all new hosta divisions (before tissue culture, all commercial propagation was field grown, hand division) in a 5-10% bleach solution. Mom had traveled to various Midwestern USA nurseries/greenhouse operations during the 50' and 60's, seeing lots of nematode infestations in commercial field grown perennials beds. Her conclusion was these plants were then distributed around and thus we had non-native nematodes coming into the beds with plantings of these plants, before hosta.

Bleaching has minimized nematode problems for us - I still have much hosta stock from earlier days - and still "bleach" all my divisions. Last weekend I finished dividing 100+ clumps and had seven 18-20 gallon blue plastic tubs with bleach solution in operation! remember to keep these in the shade and use cold water - hot water bleach will kill hosta divisions quickly! If it is mushy, it is dead!

If I get a "keeper" hosta that I need to rid of nematodes, I will divide it down to singles, cut out all woody tissue and leave in bleach solution overnight. Set it aside with notes that it was infected and watch it for a couple of years - repeat if necessary.

I have thrown out more plants recently (not worth the effort for big yard with many plants). I also used Terrachlor (no longer available I think, if you can get some old stock use it!) and sprinkled in the soil after digging the plants. More chlorine-based poison!

Hope this helps - nematodes can be managed when some sanitation and proper watering.


Bruce goes on to say:

I should add that dirty clay encrusted divisions need to be bounced hard and broken up, to remove the dirt. Any organic material in the soil or inorganic clay/sandy soil will take up the bleach and you will have dirty water! If I can't smell bleach or see the divisions, change to new bleach solution.

Leave them soak a couple of hours, depending on size. Smaller divisions less, thicker heavier divisions longer.

Yes, I have sprayed 10% bleach around infected soil, but for the above noted reasons ( I am a chemical engineer by degree, working in soil microbes now) the effect is negated, unless you use huge amounts for longer lasting treatment.

Why I don't bother with ZeroTrol - too expensive and not long enough lasting in the environment for what is claimed.

Yes, diluted bleach is an old remedy to kill germs and microbial pests. Chlorine is short-lived but nasty to these life forms. Larger and more concentrated amounts are nasty for humans as well.

With that all laid out it wasn't difficult for me to decide what to do. I wasn't about to destroy the infected plants, so seeing as there is always bleach around our house I mixed up an 8% solution, uprooted the plants in question, removed all leaves showing infection, including ones where you could barely notice it, divided them and repotted them in #1 pots that had been cleaned and bleached as well.

While I have been talking in terms of a bleach solution of 5-10% as the range recommended by Bruce Banyai, the hypochlorite dilution is actually much lower, BUT, it will depend on the brand of bleach you buy as to what the actual dilution is. That will have an impact on the effective working strength of the product you are aiming for. Haven't looked at a bottle of name brand bleach lately, but if memory serves it likely is a 5.25% hypochlorite solution, but I have seen no-name brands @ 3.85% (that's how come they're cheaper).

The varieties that first attracted my attention were 'Fire Island' -this one here- and 'Tattoo'. In addition to some holes from hail damage you can also see the nematode infestation quite clearly in the leaf on the far right.

All the old growth leaves were removed, not worth saving. Then the plant was divided - I could actually break the divisions apart by hand, did not have to resort to using a knife and having to deal with disinfecting that.

Next were the 'Tattoo' divisions. As you see, they're really quite infested and all the older leaves were removed and only the most recent ones were left, as I felt there should be some leaves and there was no evidence yet of the development of new growth from apical buds.

Originally I received one plant of 'Tattoo' and when I went to pot it up I saw an opportunity to break off one division and ended up with 2 plants subsequently. The one with 2 shoots was further divided this time and as you see I was so brutal to it I removed all the current leaves, leaving naught but the crown.

A quick glance of 'Ray Of Hope' did not show much in terms of actual leaf damage, but there was ample evidence of new offsets. Closer inspection showed lots of areas of concern however and rather than try and save some leaves, they were all removed and what is now left are 2 divisions with big root systems and a couple of new shoots each.

They're all potted up now, though I must admit that somewhere in the potting process I lost track of that small single shoot 'Tattoo'. I'll have to go digging and see where it is. Probably tangled up in another root mass, or is that mess...or it might have gotten tossed with the discarded leaves by accident, I'll never know.

The sudden realization occurred that the situation might actually be worse than originally assumed. These three varieties are part of a shipment of 8 and upon their arrival they were unpacked and left to soak in a bucket of rainwater for 5-6 hours. Over that time frame it is quite possible, if not likely, that even if there was only one infected plant to begin with, over that length of time the others would have been exposed to the dirty payload carried by the infected plant. In my ignorance I might very well have infected the lot of them, however inadvertent. Needless to say the others will be under close scrutiny for the next few weeks left prior to senescence, as well as the coming growing season of course.

The picture below shows a cropped detail of a couple of the 'Tattoo' leaves, taken the day they arrived here: August 11th, 2007. You can see the start of the characteristic interveinal browning already. At the time I did not recognize it for what it was, this is one of those hindsight matters. If I'd known what I was looking for/at, I likely would have recognized it for what it proved to be and would have dealt with it then. Look closely near the top left and bottom center.

About 3 weeks later, September 1st to be precise, the infestation is much more noticeable. Just look at these next three shots and notice the damage to the interveinal tissue, not a pretty picture.

A lot of people upon seeing the first signs of potential trouble will take the affected leaf, float it in water for 24 hours and the next day looks for the presence of worms in the water with a strong light and a magnifier. This was so blatantly obvious to me, even though it was a first time experience, that I didn't bother going through that step.

Two weeks later again and it surely looks as if the saga continues. This here is 'Wylde Green Cream' and while it may not be as heavily infested as the 'Tattoo', it most certainly is and I guess it's one more round of bleach bath to deal with this one. With this one that makes 4 out of 8 that shared the same bucket of rainwater to show foliar nematode damage. The remaining four show no signs thus far, but I'm not prepared to give them a clean bill of health as yet. Next year all 8 of them will be kept away from other Hostas and in an area where they will see plenty of light but no direct rainfall, they'll be watered by hand in their pots. By not allowing rain to fall on them there will not be the film of water they need to spread around, so if there are still infected ones they will not be able to spread their dirty payload.

To top it all off, this is what I saw September 16th on 'Miss Grace' and that for me was the last straw. Why do I keep hoping they won't show nematode damage, only to be disappointed next year? Why take a chance? Why not take the bull by the horns and deal with them all, cut off their foliage, bleach bathe the remaining crown and roots and repot them? Yes, I know it's late in the season for re-establishing roots and perhaps one or two will be a no-show next spring, but I'd rather have tried the bleach bath on all of them and have the survivors clean and clear of nematodes than to pitch them all. And if one or two don't come back up in the spring, too bad, unfortunate, but that's the way the cookie crumbles, you makes your bed and you lie in it.

Hope springs eternal though, doesn't it? It's October 6th 2007 and this is one of the four 'Fire Island ' divisions. Looking pretty good, what? I ended up with 4 divisions of 'Fire Island' and I can't wait to see what spring 2008 holds for them.

I must admit that I was a little concerned over how well I would fare with Ice Age Trail after the bleaching I gave it mid-September. It was very gratifying therefor to notice by October 21st that the crown is showing 2 new buds as you can see, my biggest concern now will be to make sure they make it through the winter; a bit of extra mulch will go a long way to help with that.

It's now early March '08 and there's this bloody rodent that's been ravaging our lilies and it has now gone as far as digging up Lily bulblets and scales and dropping them in a couple of pots with Hostas, like this pot with 'Deja Blu'.....

... or this pot with a 'Wylde Green Cream'. It must use this batch of pots as a roosting place as most of them have rodent droppings in them... the left red arrow shows a lily scale and the two right ones point to rodent droppings.... thank goodness at least it/they haven't gone after the Hostas... yet. These two pots are part of the bleach bath batch described above. As said, they're all being kept together, sheltered under cover so there is no chance of splashing rain passing on the infection to the rest of the plants. By late July/early August I should have a fair idea as to how successful these attempts were. It's encouraging at least that most of them are already showing swelling apical buds, that bodes well. While all of these 'bleach babies' are now on the lower of two shelves, once they start to show noses and signs of unfurling they will be moved to 'the upper deck' because they'll want to see more light than what they'd be getting lower down.

As an aside, I'm somewhat thankful this rodent has not gone after my hostas at all. I keep reading about people in other parts of North America having to protect potted Hostas from rodent damage, in particular when the pots are close together and covered with some form of mulch for winter protection, but at least this one hasn't bothered them at all. And won't either, seeing as it fell victim to its penchant for lily bulblets.

I'm very happy to report that for 2008 all except one of the 'Tattoo' have come back up, some with quite the vigour I might add. Now let's see them put on some more size and let's see how they all look come August/September.

It is now August 2nd, 2008, and I must admit great concern over what I have just discovered on my 'Ice Age Trail', it is all too familiar from last year. I have not yet removed the leaf and put it into a glass with water overnight to check for the suspected presence of foliar nematodes. Yes, it's only the one leaf on the one plant, but I'm choked.

Still haven't been able to locate the folding loupe I have from distant times somewhere, but, we're now 2 weeks after the picture has been taken and there are no signs the 'affected' area has grown any bigger, and that somewhat surprises me. Nor does it seem to have spread to between additional veins on the same leaf, nor are there any other leaves afflicted in this fashion. Strange.

We're now into late July 2009 and I feel an update is in order. None of the surviving 'bleach-babies' have shown any signs of returning foliar nematodes. All of them were kept in standard black plastic nursery pots, mostly 1 gallon. Some have done somewhat better than others, but I suspect that boils down more to an issue with the potting mix than anything else. The pots have been kept in a covered area, on a fairly high shelf where they receive pretty much full sun. And since the area is covered there is also a fair bit of heat gain, temperatures can easily reach 90+ºF and with the black pots soaking up all that sun I have no doubt the soil temperature is quite a bit higher than that and I cannot help but feel that the high soil temperatures have had an impact on the foliar nematodes if there still had been any. While undoubtedly the bleach treatment is and was the first and primary line of attack, I have this suspicion the higher than average soil temperatures made an added contribution to deal with the possible recurrence of an infestation.

Because there have not been any further signs on any of them since last year's suspicious 'Ice Age Trail' dessicated white portion of one leaf shown in the last picture above, I felt comfortable enough this spring to plant out one of the 'Fire Island' divisions. I have seen this dessication of white areas in other variegated varieties and have little doubt the cause is more related to sun-exposure and water availability than anything else. Others that will follow soon into the yard are 'Thumbs Up' and 'Ray Of Hope', both of which have shown great vigour. While the area these plants have been kept in was chosen primarily to keep them away from the main stock of Hosta, the heat they have endured for the past 2 years I suspect may have had more of an impact than I perhaps initially realized.

Fall 2010 is upon us and I'd say we're overdue for an update on this issue. Of the batch I originally received I have lost 'Tattoo' and 'Miss Grace', both to crown rot, most likely caused by poor draining potting mix. The remaining ones, 'Ice Age Trail', 'Thumbs Up', 'Wylde Green Cream', 'Ray of Hope' and 'Fire Island' are all showing no ill effects of the treatment and no further signs of presence of foliar nematodes. I remain cautious however, after all, we're only 4 years since I noticed the little buggers. 'Ray of Hope', 'Fire Island' and 'Thumbs up' have all done quite well for themselves, with each of them having yielded additional divisions.

Spring 2011, and it would appear 'Wylde Green Cream' succumbed to crown rot over the winter. The 4 remaining varieties out of this lot are all doing quite well. 'Ice Age Trail' now has 6 shoots, there are two sizeable division of 'Thumbs Up', 'Ray of Hope' is going gangbusters, has been divided a couple of times already, and has lived up to its reputation for settling into the edge-variegated form called 'Roller Coaster Ride' on a couple of shoots, and 'Fire Island' is coming right along and continous to be a favoured bright beacon in the spring with its bright yellow leaves.

All's not well however. Early August 2011 I was horrified to discover foliar nematodes where I had not expected them. They're in a 'Maui Buttercups' in my large raised planter I use for growing out hostas and I'm more than puzzled as to how this particular plant ended up infested. It was dug up with a generous amount soil and both were disposed of. It's not the only 'Maui Buttercups' I have and couldn't be bothered trying to save it. The hole it left was filled with a kettle of boiling water, which should have taken care of any remaining nems in the soil. Thank goodness none of the others nearby showed any signs, but needless to say I'll keep a close eye on things for the next couple of years.

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