Friday, July 20, 2012

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.