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)


12 thoughts on “What Makes Hydrangea Leaves Stick Together?

  1. patty

    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. 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

  4. 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

  5. 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!

  6. 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?

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