VAL BOURNE’S GARDEN WILDLIFE
Why netting won’t defeat all brassica pests
WHO said being green was easy? Certainly not me. There’s no magic wand involved in eco-gardening, but I am a keen observer. I spend a lot of time looking and, if I see a problem, I nip it in the bud. That means either rubbing pests off with my fingers or ‘big booting’ them underfoot, and looking for any diseased leaves that need plucking off.
My brassicas are all grown under netting to stop large and small cabbage whites laying eggs. The butterfly netting is a double-edged sword however. It lets smaller insects through, and that can be good, but restricts birds from picking off pests – and they will eat small, newly hatched brassica-eating caterpillars. The net doesn’t prevent marching caterpillars gaining access, as I discovered on the allotment one year when I followed a trail from a nearby plot to mine.
While peering the other day, I spotted a hundred or so newly hatched cabbage white caterpillars on a corner plant of the kale patch in the garden. I cut the leaves off, although the slightest tremble sent several dropping to the ground to hide away. I gathered them all up and gave them the big boot treatment and so far none seem to have migrated to the rest of my kale plants.
As I touched my caterpillar-ridden kale plant a little white cloud puffed up. This is the cabbage whitefly (Aleyrodes proletella) which is a different species from the greenhouse whitefly (Trialeurodes vaporariorum). Both cause enormous problems in commercial crops because whitefly suck a lot of sap for their size, spreading viruses as they go. They also produce masses of honeydew resulting in black sooty mould.
Most are resistant to pesticides so commercial greenhouse growers producing a monoculture (i.e. one crop like tomatoes) struggle once they have an infestation.
However whitefly are predated by specialised wasps, ladybirds and some bugs and I suspect hoverfly larvae devour them too. These predators can get through my netting and into my open greenhouses. Also on the plus side, whitefly are subject to fungal attack in warm, damp conditions.
And I’m wary about cutting tomato foliage off low down, because this is where whitefly predators such as adult ladybirds, their larvae and eggs tend to lurk. A cold winter does kill whitefly: most of the 2,500 species of them in the world need warmish temperatures to survive.
“Butterfly netting is a double-edged sword”
Net brassicas and grow them in the garden – rather than the allotment – where you can keep a very close eye on them These cabbage white caterpillars have slipped through the net