I tend not to go away much in July and August, and that is partly because I don’t like leaving my previous veg plants to fend for themselves. This year, however, I did end up going away for a couple of weeks, and I came back to some very sad looking brassicas. There were caterpillars everywhere, and for every caterpillar there were several holes eaten out of the plants.
When I first started out growing, I would have seen this as a complete disaster and pulled up the plants in defeat. But actually, all is not lost, even when the caterpillar damage is quite severe. Plants can survive a fair bit of damage.
I have pulled up some plants – like the Red Russian Kale that also looked to be suffering from some other problem as all the leaves were stunted and curled (I think probably Swede Midge) and have put that on the compost pile. The I collected up as many of the caterpillars on the remaining brassica plants as I could and added them to the compost pile too, so they can eat the kale. I checked the centres of each plant to make sure that the new leaves emerging were caterpillar free and not too damaged, and now I have left the plants to it, expecting them to make a good recovery.
Interestingly, as I was collecting up caterpillars, I saw a lot of parasitic wasp cocoons – they look similar to caterpillar eggs, but more oval and in a downy kind of cocoon, usually with a dead caterpillar next to them. These parasitic moths lay their eggs in the caterpillars and when they hatch they have instant food supply and kill the caterpillar. Nature at work.
Anyway, my point is, that if your brassicas have been badly damaged by caterpillars, don’t give up on them just yet. Remove as many caterpillars as you can, check the growing centres, and hope for the best.