Backyard CSI

I love the chance to be the amateur detective and do a bit of backyard CSI when a perfectly good plant suddenly gets crook. It happened recently with these cheery people, pink pelargoniums in a hanging basket. The problem is that this is how they looked last spring. They were a happy family back then. This spring they were on the slab. Something was doing them in, and it wasn't pretty.

Let's start with the victim, back in the days when it was a healthy hanging basket of pelargoniums. The problem was, where it hung out, it was a sitting duck.

It was a mugging, a gang mugging. 17 culprits – count them – 17 curl grubs munching on the roots of my pelargoniums. These plant muggers can be found everywhere – under lawns, in pots or in garden beds – they're not fussy. They're the larvae of the common black garden beetle and they're very widespread here in Australia.

This is the classic curl grub mugging scenario. Hanging basket with an outside light nearby. You'd think a light would provide some safety, but not from curl grub muggings. In fact, the beetle mum is attracted to the light at night, finds a patch of soil conveniently nearby, and she lays a clutch of eggs. The eggs hatch in the soil and immediately start eating the roots of any plants they find. They're not fussy; they'll eat just about anything. They love lawn grasses, but pelargonium roots will do just fine if that's all that's on offer.

After I removed all the poor little emaciated pelargoniums from the basket they were all virtually bereft of feeder roots. Just the more stout tap roots and nothing much else.

Here's a close-up of the curl grubs. They're usually white and curled up like this. They look like sleeping babies but that's just a front when they feel threatened by bright sunlight. It's OK to handle them with your bare hands, as the hairs aren't nasty, as they can be with some caterpillars.

I dispose of the grubs by tossing them onto the roof of my shed, where the local magpies quickly swoop down for the free feed. In fact, if Aussie readers/gardeners ever see our native magpies standing on a lawn looking a bit odd as they turn their head sideways as if listening to something under the soil, that's exactly what they are doing. They're listening for grubs such as curl grubs munching and moving just beneath the soil.

My pelargoniums were so sad that I bought a punnet of three identical seedlings and planted them into new potting mix, but I trimmed up the best of last-year's plants and planted them in between the seedlings. Hopefully they'll recover and belt along like they did last year.

And so a more optimistic photo seems the right one to finish with!

As a general tip for gardeners here in Oz, if you have a potted plant which used to be doing fine but is now struggling, despite all your best efforts at watering and feeding, think 'curl grubs' first and foremost. There's only one way to check for them: unpot the plant completely. Go through the soil with your hands very thoroughly, as the grubs will probably be numerous and everywhere, from the top of the soil down to the bottom, along the sides and in the middle.

If your 'problem' pot is somewhere near an outside light of any sort, that's the curl grub's classic MO (love the detective talk). Book em, Danno!