What’s That White Stuff on My Crape Myrtle?

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Mysterious crusty white stuff on the tips of my crape myrtle’s leaves.

So the other day I noticed my Tonto crape myrtle had this crusty white stuff on it. Not powdery mildew, which sometimes appears later in the year on crape myrtles. Mildew looks like white film on the leaf’s surface. Mine had white stuff on the tips of the leaves.

My first thought was woolly aphids or cottony scale, but it didn’t seem to be a critter. The white things didn’t move when I poked them, and they had no discernible body parts. Weird. So I googled it.

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This ant has found a sweet treat.

It turned out to be something totally harmless, but I wouldn’t have guessed what it was.

The white stuff was plant sap that had oozed out of the leaf tips in a natural process called “guttation” and then dried and crystallized. The crystals are composed of potassium and sugars and are said to be sweet-tasting. I tasted one, and my resource (Walter Reeves) was right on! That’s probably why that ant is in the picture.

(Let me add that I don’t recommend tasting plant ailments as a method of diagnosis, however.)

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Guttation on a strawberry plant.

I remembered learning about guttation in HORT 101. It looks like dew, but it’s not. The drops come not from the surrounding atmosphere but from within the plant.

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Droplets on the edges of poppy leaves.

It’s not transpiration, either. Transpiration is how plants usually move water from the roots to the atmosphere, but in transpiration, the fluid exits through openings on the undersides of the leaves, called “stomata.” In guttation, the fluid exits through special openings on the edges of the leaves, called “hydathodes.”

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Acaena inermis ‘Purpurea’ is cute enough already, but with sparkling drops of water–adorable!

Guttation happens most often when humidity and soil moisture levels are high, and is best observed shortly after sunrise—before the sun’s rays “burn off” the droplets and they evaporate into the air.

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Alchemilla mollis is a master of guttation.

Guttation. What an awful word! It sounds like a medical condition: “If you suffer from moderate to severe guttation, ask your doctor about Zanthinox.”

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California poppy on a cool, balmy morning.

Or at best, a construction term: “The old house was in such bad shape that a complete guttation was in order.”

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Lamb’s ears, or Stachys byzantina, exudes water droplets through guttation and holds them there with its fuzzy foliage.

Guttation looks like the work of garden fairies who have been up all night bedazzling the garden. Surely it deserves a prettier name.

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When droplets produced from guttation dry, they may crystallize.

Although, granted, sometimes it does end up looking like cottony scale.

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4 Responses

  1. Jane / MulchMaid
    Jane / MulchMaid at | | Reply

    “Guttation” may not be a very lovely name for the process, but the name for the openings in the leaves from which it comes, “hydathodes” is nice – kind of like a Greek nymph.

    I learned about guttation once before in my life, but as I mostly do, I forgot. Thanks for the refresher!

  2. Casa Mariposa
    Casa Mariposa at | | Reply

    I’ve never heard of this but do agree the name is wretched. It sounds like it involves toilet paper and a locked door. But I do like the idea of plants being covered with little sugar balls in the morning. Maybe I should throw a few in my coffee.

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