What is Wrong With My Hydrangea Leaves?

Apr 13, 2017 | Gardens

This is the question I asked myself for three years. The first year I noticed the brown-gray “knitted” look on my leaves I thought it was wind damage. In 2014 we’d had a spring wind storm after the leaves had emerged, and I thought that’s what caused the damage I was seeing. But when it returned in 2015 and 2016, I knew this wasn’t the case. I hadn’t used any products on or around these shrubs – no herbicides, insecticides, or even fertilizers – so I doubted that the damage had anything to do with these or the weather. Finally, in the fall of 2016, I sent the samples off to the University of Massachusetts Diagnostics Lab for analysis.

This is part of the lace-cap hydrangea where the symptoms were originally spotted in my yard. The first year they weren’t so bad, but the population of thrips much be growing every year because by the third year this plant was really looking pretty pathetic. See photos below.

Tawny Simisky, Entomology Specialist with UMass Extension, contacted me a few weeks later with her initial diagnosis of an insect I’d never heard of: chilli thrips, aka Scirtothrips dorsalis. She asked for more samples, and I sent some as did Russell Norton, Extension Educator with Cape Cod Cooperative Extension, who had seen similar damage on other hydrangeas in the region. After having her initial diagnosis confirmed by several other Extension specialists and the USDA, she confirmed that this was the first time that chilli thrips had been seen in Massachusetts. Oh great. Not a first I really wanted to be part of!

But here we are, and I post these shots of my plant, along with this link to the fact sheet from UMASS that has more information about this pest and possible treatments, so that if your hydrangea leaves start to have a similar look, you’ll have someplace to start for information.

This shot is typical of the damage on the lacecap that’s been infected for three years.

Here is another mophead hydrangea in a different section of my yard. In 2016 I noticed that the symptoms that I’d originally seen on the lacecap had spread to two other plants, including this one. As you can see the discoloration isn’t as bad on this plant, because the population of the thrips isn’t as great here.

Here is how the first-year-infected mophead looked from a distance. You can see in this photo that the foliage is just a bit curled, and has a bronzy look to it, especially compared to the plant on the left which didn’t show symptoms last summer.

So, the question, of course, is what am I going to do. Russ Norton, at the Cape Cod Cooperative Extension, tells me that although the ingredient spinosad is recommended as a treatment, the problem with using this is that thrips can become immune to it over time. So for the moment I’ll refrain from using that on my shrubs. Last fall I cleaned all the fallen leaves around these plants and bagged them for disposal. I don’t normally do that around hydrangeas, so it will be interesting to see if this helps. Secondly, once these plants break dormancy I’m planning on spraying repeatedly with horticultural oil, just to see if that can suppress their populations…it can’t hurt, is my thinking.

UPDATE 8/2018: Cleaning up fallen foliage around the plants in autumn seems to help but it’s not a cure. I haven’t kept up with the sprays, but I will do so next season as this year I see quite a bit of damage. I plan to try Bonide Mite X which is labeled for thrips.

Although the fact sheet lists the many other plants this non-native species of thrips is known to attack, including many agricultural crops, right now in MA it’s only been seen on hydrangeas. Just our luck, Cape Cod…our signature plant! Well, as Gilda Radner’s character, Rosanne Rosannadanna, used to say, “It’s always something!”

Yikes.

 

8 Comments

  1. Betsey Godley

    I’ve seen that type of damage on Bloomstruck. actually several different Bloomstruck in several different settings including a local garden shop. I’m curious which macrophylia the thrips have effected in your garden?

    Reply
    • CL Fornari

      Betsey,
      I don’t think we can say that some are more prone to these than others. You should keep an eye on the plants closest to your Bloomstruck this summer to see if it’s starting on others. For two years the damage was confined to my lacecap, Grayswood. I didn’t know it was thrips at that time, but thought it might be a virus on this plant. But last year it spread to an unnamed macrophylla that was on my property when we bought the house – it’s not an Endless Summer since it’s shorter and the flowers are smaller, but I don’t know what it is. I also saw damage on one of my Forever and Ever plants. There has been no spread to the other shrubs on my property, including my Bloomstruck. I intend to spray all my plants with hort oil this weekend to see if that might help.

      Reply
  2. Betsey Godley

    Thanks for the info. I have a Grayswood serrata here and although it hasn’t showed signs of damage, I’ll keep an eye on it this year. My Bloomstruck had a good amount of winter damage and has been disappointing for the last 2 seasons. It will likely be thrown away if i see signs of thrips or other leaf damage. If I don’t see any leaf damage or issues, I’ll pass it on to someone with more patience or a more forgiving garden site. I’ve printed out the Thrip data sheet to share with my fellow gardens and I’ll keep a close eye on all of my hydrangeas this year.

    BTW, I had the pleasure and privilage to participate in The Big Dig this year. Thank you so much for opening your garden again to the MGs!

    Reply
    • CL Fornari

      I’m sorry your Bloomstruck didn’t do well over the winter…I’ve seen many hydrangeas in great shape this spring but others not so much, and I think it’s largely a matter of wind exposure. Glad you’re keeping an eye on the chilli thrips situation – I’m anxious to see if my oil sprays help…

      Thanks for helping with the MG dig! Susan and the Big Dig Team do a great job.

      Reply
  3. carol ebreo

    I wonder if that could happen to ajuga Black Scallop. I dug a lot of it thinking it was a fungus as the leaves were all curled. ??

    Reply
    • CL Fornari

      My guess is that it is fungal damage on the Ajuga, Carol. So far these thrips seem to be very host-specific in our area, although in the south they go after peppers and other members of the Solanium family. Curled leaves can be typical of white-fly or aphid damage as well. Did you check under the leaves to see if you can find any sign of insects?

      Reply
  4. stephen manning

    My Hydrangia has like a white deposit on the leaves wich make them look grey the affected leaves are really brittle and will snap at a touch until this year it has been a picture of health what can i use to cure it Steve

    Reply
    • CL Fornari

      It sounds like powdery mildew. Spray with an organic fungicide and clean up fallen leaves and dispose of them. No cure for this year but the fungicide with dampen it down and the cleanup help for next season.

      Reply

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