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What Makes Hydrangea Leaves Stick Together?

20170610A Lieuse (LH)
Hydrangea leaves glued together by the leaf-tier. Photo: http://www.laidbackgardener.wordpress.com

The ever-popular ‘Annabelle’ hydrangea (Hydrangea arborescens ‘Annabelle’), with its big pompoms of white flowers is often attacked by the hydrangea leaf-tier (Exartema ferriferanum), as are other white-flowered smooth hydrangeas (H. arborescens). It’s a small brown moth whose larva has the annoying habit of gluing hydrangea leaves together at the stem tip. Thus sheltered from any predator, the small green, black-headed caterpillar can munch away to its heart’s content on the tender young leaves and flower buds trapped inside its shelter.

Not only is this unsightly, but it often prevents that stem for flowering at all that year… and you didn’t grow ‘Annabelle’ for her foliage!

After about ten days, the caterpillar stops eating and morphs into a chrysalis. About a week later, the adult moth appears and heads off to spend the summer… who knows where? But then it returns in late fall to lay its eggs. There is only one generation per summer.

What to Do?

20170610 Laboratoire de diagnostic en phytoprotection - MAPAQ:Diagnostic Laboratory, Crop Protection, Ministry of Agriculture,JPG
Here’s the culprit, hiding among its excrements inside the sealed leaves. Photo: Diagnostic Laboratory, Crop Protection, Ministry of Agriculture

To nip the current season’s infestation in the bud, open the leaves manually, then hand pick the caterpillar and either crush it or drop it into soapy water. If you do that soon after the leaves are tied together, you’ll save that season’s bloom.

To Prevent Next Year’s Infestation

Saving hydrangea flowers by opening the leaves one by one is not such a chore when it happens just once. It’s a major annoyance, though, when it happens annually. And once the leaf-tier is in your neighborhood, it does tend to come back year after year. So you’ll need a different strategy to control this pest.

It’s important to understand that the moth lays her eggs on hydrangea stems in the late fall, usually only one per stem. The eggs overwinter there, then, in early spring, as the shrub buds out, the young caterpillars crawl up the stem and invade its upper leaves. And that gives you a way out.

Early in the spring, cut your smooth hydrangeas (remember this insect attacks only that species: more on that below) back as close to the ground as you can. Since this species flowers on new wood, this will not affect its blooming. But if you pick up and compost the cut stems, you’ll have eliminated the leaf-tier’s eggs, thus preventing the infestation.

Well, nearly….

You see, the female moth tends to lay her eggs low down on the stem, sometimes so low you can’t cut back that far. Still, if you prune the plant back to about 4 inches (10 cm), you ought to get most of them. You can then open the tied leaves of the few insects that do survive as soon you notice them.

Another possibility is to spray the stems with Btk (Bacillus thuringiensis kurstaki), a biological insecticide, as soon as they show the first signs of growth. That will kill the caterpillar as soon as it emerges from the egg.

Not All Hydrangeas

Note that the leaf-tier attacks only one species of hydrangea: smooth hydrangea (H. arborescens). There is no need to prune, spray or otherwise treat any other species.

20170610 Proven Winners
Pink-flowered smooth hydrangeas, like Invincible® Spirit, seem immune to leaf-tiers. Photo: Proven Winners.

Also, I’ve been surprised and pleased to see that the insect doesn’t seem to be interested in the new pink-flowering smooth hydrangeas, like Invincibelle® Spirit II, but seems to stick to the white-flowered ones. Is that just a fluke or are other gardeners experiencing the same thing? Do let me know!20170610A Lieuse (LH)

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

23 comments on “What Makes Hydrangea Leaves Stick Together?

  1. I have found this worm (thanks for the name) over the last few years on my Annabelles here in southern Ontario. I’m too squeamish to pick them out of their home so I have been pinching off the buds, sometimes in time to get blooms and sometimes not. For some reason I did not get the worm this year. Lucky? Probably not. They’ll be back. 😉

  2. Christal Wall

    I have both white Annabelles and the pink Invincible Spirit variety. While the infestation isn’t nearly as bad on the pink’s, the worms are still there. I am nearly at my whit’s end trying to control these pests! My Annabelle hedge used to be huge and quite showy, now it is quite spindly and the blooms are not nearly as large as they used to be. I have been battling the leaftier for about 5 years now here in southwest Michigan.

  3. Pingback: Honey, They Shrunk the Hydrangea! – Laidback Gardener

  4. sue mitchell

    squeezing the pods to crush this monster seems to save the flowers but next spring im going to yry yo cut to the ground and then spray keep your fingers crossed

  5. Lori Boufford

    This information was very helpful to me. It was extremely well written and easy to understand. Thank you very much for taking the time to post it

  6. 04043 Vanilla Farm

    thank you so much for this article, I have been struggling with this monster for the last 3 summers, but as I prepare for fall now, in zone 5, tell me why I am not cutting the annabelle back now to 4″ and instead waiting till “early spring” as your post suggests? Thanks!

    • If you cut back now, the female may not yet have laid her eggs (she does so very late in the season) and will lay them on what’s left of the stem. If you wait until spring, it’s possible she’ll have laid her eggs higher up than you pruned, reducing the population.

  7. Colleen Johnson

    This is my second year experiencing the horrible leaftier in my Annebelle hydrangeas. It’s so disheartening as my newly created berm highlighted with 12 of these plants was created only 4 years ago. The first 2 years the area looked OUTSTANDING but year 3 my garden was struck with thus horrible work. I treated 2 times with Malathion as the local garden center diagnosed them as looper worms. Not much success, straggling plants with sorry small reduced quantity blooms. Now this year I totally ran across this information as I googled what makes hydrangea leaves stick together. OMG I was treating for the wrong thing and just noticed yesterday that it’s back on my plants again. Hopefully, I can do a combination of clipping off the damaged areas and spraying. I’m sick over this mess and certainly don’t look forward to next year and the thought of this being annual headache. I spent way too much in hiring the new landscape area 4 years ago to only have had 2 years of nice looking plants before this infestation. How often do I need to spray as the season goes on?

    • There is no use spraying BTK once the tied-together leaves appear. It will only work on exposed larvae, the ones that have hatched, but have not yet sealed themselves in.

  8. Christine

    Thanks for the article I had no idea! I’m way to squeamish to open And squish the bug can I clip the leaf ? I have a combo of these closed leaves and buds on my snowball. TIA

  9. Just as bad on my Invincibelle Spirit II as on my old Annabelles, I’m afraid…
    Thanks for the article!

  10. I spent 3 hours opening each glues bud and I was so angry that I went looking for each little bugger. I had a bowl of soapy water and dropped several dozen. Close to 50 worms into the water, they died instantly. I also sprayed the opened bud with dish soap and water, just for good measure. I hope I at least get some flowers this year. I’m definitely treating the ground early spring!

  11. Thanks for posting! Very helpful! My annabelles had so many of these pests this year. I didn’t have the patience to open each one so I just cut them off and placed in soapy water. I know I won’t have as many blooms this year. I have another hydrangea bush beside it and haven’t noticed any of these pests. I forget what it’s called but the blooms are pink and the bark appears red.

  12. Deb Minion

    Leaf-tier eh? I have so many Annabelle hydrangeas as I love the big white blooms against my 1872 home! First year to get them so I unglued each of the glued-together leaves and crushed the little stinkers! Thanks so much for the info, hopefully I killed them in time to have a few beautiful blooms this summer!

  13. My home is 1882 and I have Annabelle Hydrangeas. Must have been popular back then. I also have been combating these worms. It took me 3 years to finally get the problem identified. I go out every morning and open 100 leaves, find the worms and crush them. I do cut mine down each fall, usually later around the middle of November, so my infestation must come in the spring. If I spray them as they grow in the spring with soapy water will that kill the moth and the eggs?

    • If you get the spray at just the right moment, you can kill the moths or the young larvae, but that’s very hard to time. Soap will not the eggs.

  14. Danielle

    My Invincibelle Spirit II had this this year. Weirdly it seemed like it was keeping the buds safe until they opened. It is covered in blooms but am also noticing it on my wee white hydrangeas nearby. The buds seem fine on all plants but super interested to find out what it was that was causing it. Will be sure to cut down lower in the future and be prepared to spray.

    • I think it’s the same darn leaflier moth. Moth lays their larve in LATE FALL like November so that’s why it’s often missed in Fall
      clean up. Supposed to spray with BTK before early spring leaf break And if you’re unfortunate enough to live somewhere, like myself, where this moth is in the neighborhood one year it’s quite possible it will be there every year. I tried opening all the stuck together leaves and there was like over 50 per plant and I have 12 plants so the job was overwhelming. I end up losing ATLEAST half my blooms. My local nursery said I could try cutting every plant down to 4” from the ground along with spraying the BTK but not guaranteed at all. I feel like cutting all my plants down.

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