Tony Dickerson problem solves
Q Are cabbage caterpillars a problem on kale? Mrs P Harding, Woo on, Bedford
A I can’t recall ever having a problem with cabbage white caterpillars on kale. However, thinking a little further, it’s nothing to do with kale being resistant to these voracious pests. I grow kale as a winter crop and cabbage butterflies are simply not active. The key here to avoiding the pest problem is timing.
If you’re keen on your cabbages and anxious to avoid caterpillars, aim to crop your brassicas over the winter. Late winter cabbage, spring cauliflower and kale can be sown in July, or even August, in the protection of a cold frame or greenhouse for planting out before the autumn. Alternatively, get mail-order plug plants. Even these late plantings will not be immune from another brassica pest – pigeons – so net the crop. Many gardeners construct quite elaborate cages, which is all very well until we have unexpected heavy snow and they collapse. I find that 1.8m (6ft) long posts hammered in the ground every 3m (10ft) or so, with nylon rope stapled to the top of the posts, makes a quick support for anti-bird netting. This can be pegged to the ground but is very easy to roll back for harvesting. If you can’t
do without your summer brassicas, the birdnetting can be replaced with butterfly or other fine netting. Other options include handpicking the eggs twice a week when the butterflies are active. There’s a biological control available called Fruit and Vegetable Protection, as well as various insecticides, including those based on pyrethrum.
In each case, follow the label instructions regarding number of applications and the harvest interval between spraying and picking the crop.
There are quite a few crops whereby you can avoid pests through timing. Growing early peas will avoid the twin problems of pea moth and powdery mildew, while a mid-June sowing of carrots might just avoid the different generations of carrot root fly.
Sowings in March of early cabbage, calabrese and summer cauliflower may all just mature before the peak of cabbage white butterfly activity in late summer.