A dead-end trap crop

A “dead-end trap crop”: is it the germ of a new Dr Seuss tongue twister or a surplus insult from a John Cleese and Graham Chapman sketch?  Nope, it’s the my latest strategy for dealing with the beautiful but deeply irritating cabbage white butterfly.

I like to think of our choice of a garden on a steep, shady south west facing slope not so much a tragic error in garden planning but a deliberate strategy for replicating temperate conditions in a subtropical climate.  It wasn’t an inability to use a compass that led us here.  Absolutely not. Instead it was my cunning plan to produce home-grown raspberries.

This fantasy has been somewhat tempered by our brassica disappointments of recent years.

Radishes are considered to be idiot-proof and we’ve usually managed to get them to grow, if not to actually eat them.  I like the long-rooted daikons since there is a brief interregnum between germination and gnarly inedibility.  The daikon sits happily in the ground waiting for me to make sushi. If don’t get my act together in time, there’s always the lovely white flowers to look forward to.

This year’s bash at radishes hasn’t worked out quite so well, thanks to my innovative  (a.k.a. totally ineffective) strategy for keeping the chooks at bay – a mandala of brightly coloured children’s bicycle wheels.  Evidence, if you needed it, that (a) the Goddess doesn’t necessarily protect every vegetable sheltering in a life-enhancing spiral (b) chickens are definitely not supertasters.  In fact, apparently chickens only have about 300 taste buds, and they’re on the roof of their mouths, which may explain the chooks’ enthusiasm for eating polystyrene foam (“crack for chickens” as someone once put it on a backyard chicken forum).

I’m also a serial failure at growing brussel sprouts.  Perhaps they’re paying me back for all the bad-mouthing I gave them as a child.  I console myself with the thought that it’s a bit warm in Sydney for this member of the brassica family anyway. You need to start early – I’ve heard you need to have your seeds in by November if you want tidy looking mini-cabbages and not some kind of ad hoc freeform leafy thing.

I banged in some seedlings in autumn – I’m reserving judgement but at this stage I’m not optimistic.   The “bad hair day” of the plant pictured above may be a consequence of a close encounter with the repurposed wire drawer I was using to keep the bandicoots at bay.  Since the cure appears to be worse than the disease, and the bandicoot seems to share my childhood dislike of sprouts, I’m living on the edge and letting the brussels go commando. The wire drawer, along with a bisected fan-cover, is off to provide security and support to my newly planted swiss chard and salsify.  I’m hoping the look is more “frugal locavore’s organic garden” and less “disturbed hoarder’s junkyard” but I reckon it could go either way.

And now we turn to the Battle of the Bok Choi.

Over the years my passion for purple and anaemic lust for iron-rich veggies resulted in an epic struggle to produce a decent crop of my favourite asian green, Red Bok Choi.  Cabbage whites seem to share my enthusiasm.   Bok choi butterflies would seem a more apt (and alliterative) choice of name.

My first effort – a feeble attempt to conceal my pretties underneath the generous leaves of a (ultimately fruitless) zucchini –  underestimated the persistence and acute senses of your average crucifer-loving butterfly.  Interplanting with coriander was a break through.  In Sydney, you can harvest your coriander leaves for aroundabout ten minutes before your plant goes to seed.  Growing cilantro as a kitchen herb here is an essentially doomed enterprise.  That said, stinky old coriander leaves do seem to throw the insect pests right off their game.  There’s apparently a couple of genes that are implicated in some peoples’ deep distaste for cilantro – maybe that’s a part of the genome we share with bugs.

But this year’s lone self seeded bok choi is looking more perfect than last season’s coriander-defended efforts.  Is it the chilly weather? The location inside the repurposed chicken tractor/brush turkey and possum exclusion zone? or is it… (drumroll) the magic of the dead-end trap crop?

After my embittering exeriences with kale and marigolds, I’m a tiny bit skeptical about companion planting.  But given the cruel fate dished out to our broccoli by an evil alliance of brassica loving bugs and furry critters last year, I’d give anything a try to get a bit more broc to the table.

I’ve been growing land cress a while.  It was one of the few food crops I managed grow – in a polystyrene foam box parked by the outdoor dunny – in the concrete back court of my terrace house in the rainy British north-west, back in the day.  Here in Berowra, it flourished in a damp and shady patch next to the chook yard, giving us for two La Nina years an unending supply of the “house soup” – vicchysoise hotted up with landcress, jerusalem artichokes and zucchinis.  Flatulence-inducing but fabulous.  All in all, a great plant.

So when I heard that upland cress has the reputation as a Black Widow for a crucifer-loving insects I figured I’d give it another whirl.

Sacrificial or trap crops are tasty things used to distract bugs from your favoured plants.  Dead-end trap crops, on the other hand, lure insects away from the plants you want to protect and then kill them.  Land cress, it seems, contains the spicy-flavoured glucosinolates, prompting some moths to lay their eggs on its leaves where its caterpillars hatch, feast and die.  Gruesome but apparently effective.

The seeds I ordered from the ever-reliable Green Harvest were the familiar looking upland cress (Barbarea vernis).  Unfortunately, the variety of land cress (sometimes called winter cress or yellow rocket) that’s been been tested as a dead-end trap crop is  Barbarea vulgaris, a related, taller plant with similar yellow flowers but a less rounded leaf.

Barbarea vulgaris is resistant to another pestthe diamond back moth – which produces a smaller caterpillar that’s also a lover of brassicas (to identify whether you’ve got got a diamond-back larvae, give the grub a bit of a nudge – it will give a bit of a wiggle backwards.  But hopefully not leap up and punch you in the eye.)  It’s a bit less clear about whether winter cress is quite so deadly to cabbage whites.  And then there’s the vexed question of whether the landcress in my garden – barbarea vernis – does the same job.

But it’s all going swimmingly so far.  My land cress is unchewed, and my the kids have already turned their noses up at a couple of meals of home-grown broccoli.  I’m sure they’ll be pleased to find there’s loads more to come, not to mention heaping platefuls of mustard greens, land cress, kale and (with luck) brussel sprouts.

And so the time honoured tradition of intergenerational brassica torture continues…

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One thought on “A dead-end trap crop

  1. Pingback: Gymnastic bees, virgin fruit and the birds that ate spring | Berowra backyard

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