Of mealy bugs and powdery mildew

Once upon a time, I had a comely cactus…


Mammillaria bocensis right after I got it from IKEA of all places

…and a lovely leafy plant.

Bloody dock (Rumex sanguineus)

Both were the picture of health.

Then came the evil forces in white.

Mealy bug secretions on Mammillaria bocensis
The larger hairy tufts are OK, they are a normal part of the cactus anatomy;
the smaller “pillows” are mealy bug secretions
Notice the whitish powder on the Rumex sanguineus
That’s classic powdery mildew
Short of bringing out the chemical arsenal, cutting off the affected leaves is all you can do

Mealy bugs are fairly common here in the summer when the humidity is low. Isopropyl alcohol seems to be quite effective on isolated outbreaks, but this cactus was so infested that I decided to toss it. (Yes, I admit it, I’m just a fair-weather gardener. A real gardener would have tried to remove the infestation and save the cactus. But I recently spent a goodly amount of time scraping off cochineal scale from a Santa Rita prickly pear so I didn’t have the patience and energy.)

Powdery mildew, on the other hand, is a fungal disease. Most experts recommend discarding the infected plant, but I’m not ready to let go of my bloody dock (what a devilishly fun name!) so I simply cut off the affected leaves. I’m not at all certain that the new leaves will be fine, but it’s worth taking a chance.

Talk about having double standards, but I guess I’m more attached to the bloody dock than to the bloody cactus :-).


  1. You are a 'real' gardener, and a practical one too! Time and energy are precious and sometimes you have to weigh if some plants are worth the extra TLC or not :)

  2. Powdery mildew is frustrating. Some sources say that it forms under wet conditions, and others say dry conditions. I think that there are different types that thrive under both conditions. Have you tried spraying with a milk solution? I forget the exact recipe, as I gave up spraying plants a few years ago as it just didn't seem to be worth the effort with a large patch of Monarda I once had.

    The first year I grew Verbena bonariensis it got terrible powdery mildew, but the volunteers that have been multiplying over the years have been free of it -- or at least I haven't noticed any major problems. That could be because I'm not looking too closely though because they're volunteers.

    1. Last year we had powdery mildew on our lilac. That was the first time ever since I planted it in 1998. I didn't do anything and it eventually went away (i.e. when the leaves fell). Nothing this year on the lilac, just on the dock which isn't anywhere near the lilac.

  3. It probably helped that the IKEA cactus was just that, and IKEA cactus (meaning you didn't spend a fortune on it?). Hope your Bloody Dock recovers...oh and see, you're a REAL gardener, you even know the names of the bad guys.

    1. Yes, the fact that I'd only paid $2.99 for the cactus made the decision easier. Plus, it had never bloomed anyway :-).

  4. Rumex is a tough plant, never seen it get mildew up here tho.. Powdery mildew was enough to stop me from growing monarda, what a pain! I'd cut it back to the ground and have it reflush out, it's reliably hardy anyhow. Can't save em all, even tho it'd be nice to.... poor little cactus, death to all mealy bugs!

  5. As Kenny Rodgers sang, "You've gotta know when to hold 'em and know when to fold 'em; know when to walk away and when to run." I'd say you are a REAL gardener alright. The bloody dock will NOT die, believe me, I've tried. It will happily seed all over your garden far from where it's planted. You'll have more of them than you ever wanted. You could try cutting it back and spraying emerging foliage with the following solution: 1Tablespoon of baking soda, 1/2 teaspoon liquid soap, gallon of water. Some recepies call for adding a Tablespoon of ultra light horticultural oil which "coats and smothers the fungi" but I've never added oil myself. This works but must be resprayed every week or so and any time the leaves get wet. Best to water well a couple of days before applying the solution. If yours doesn't make it come to my garden with a shovel. Please.

  6. Ooh just discovered your website and love it! I live in Brisbane, Queensland (Australia) so we have very similar climates. I'm a new gardener and was trying to figure out what has desecrated my beautiful and hitherto SERIOUSLY healthy and happy Polka Dot plant! I'd moved it to the edge of my verandah (being lazy) to take advantage of all the rain we've been having, so I didn't need to water with my trusty lemon yellow watering can (which I love using when I'm not uber busy and tired like I've been this week).

    The reception ladies at work suggested the white stuff was probably mealybugs or powdery mildew. I found the difference from your photos. It's definitely mealybugs - Gasp! Little wretches messing with my beloved Polka Dot plant that I grew from a leaf that was in a beautiful bunch of flowers a lovely elderly lady gave me when I moved into the area. It's the very first thing I've ever grown from a cutting, so I've been thrilled at how vibrantly this gorgeous plant has grown!

    So now I've removed (insert determined face here) all the affected (and some just plain dead) leaves, and squirted the heck out of the stem and leaves with the horrid cotton wool like vermin, with a concoction of Neem Oil in Coconut Oil. They were the closest things I had on deck, which resembled some of the home-made pesticide remedies found online by a lovely Indian gardener. I then used some Paper Towels to wipe off the horrid little things. It's only a day later, but my plant looks largely alive and healthy again! Yay!

    Thank you for your fab page!!



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