Growing kale is one of the pleasures of spring vegetable gardening. The sturdy seedlings survive sudden cold spells when given modest protection, so you can get an early start and start harvesting nutritious leaves by the time it’s warm enough to transplant tomatoes. Stately kale plants are pretty, too, so they are a great vegetable to mix with pansies, calendulas or other cool-season flowers as shown in this Garden Planner planting plan for spring kale.
But even easy-to-grow kale has its fair share of insect pests, and because they are so small and furtive, kale pests have special talents for launching sneak attacks. Here I will discuss the three most common kale pests in seasonal order, with links to more information at The Big Bug Hunt, where you can report your sightings.
In my climate, autumn-grown kale often survives winter and starts growing first thing in spring. Woolly, grey-green cabbage aphids also survive hidden away in tiny crevices. As the plants grow, the cabbage aphids rapidly reproduce in dense colonies, like the one shown above.
Cabbage aphids feed by piercing leaf tissues and sucking out the juices, so a badly colonised kale leaf will never recover and should be pinched off and promptly composted. You can treat small colonies of cabbage aphids with insecticidal soap, but it’s hard to kill every last aphid. Happily, vigorous young plants seem to be of little interest to this kale pest, so you can take out old infested plants and get a new start with your spring crop.
Cabbage White Caterpillars
Cabbage white caterpillars begin appearing in late spring, after you see the adult white butterflies flitting about in your garden. In addition to mating, they are laying eggs on every kale, cabbage, and broccoli plant they can find. This educational video tracks the cabbage white life cycle from egg to butterfly – a drama every vegetable gardener should understand. The small cabbage white is widespread, and in Europe the similar and even more voracious large cabbage white butterfly can leave kale plants badly damaged.
Many of the caterpillars’ natural enemies, especially wasps, are not yet present in large numbers in spring, so you must protect your plants by hand-picking your cabbage white caterpillars, using polythene or fleece tunnel barriers to prevent egg laying, or using an organic pesticide that uses Bacillus thuringiensis or spinosad as its active ingredient. In very bad caterpillar years I may do all three – hand pick every caterpillar I can find, treat the plants with Bt, and then cover them with lightweight tulle to prevent future egg-laying.
In North America, harlequin bugs wait until the weather warms in summer to appear on kale plants, and there is no mistaking them because they are so colourful. In my garden, spring-grown kale plants have passed their prime when the harlequin bugs appear, so I take out the plants and compost them rather than fight the bugs. Having the garden become a brassica-free zone for a few weeks in summer deprives all kale pests of the host plants they need, and sets the stage for fewer insects on the fall crop.
In some areas of California and Arizona, the bagrada bug, or African painted bug, has joined the list of serious kale pests. The same pest management approaches that work with harlequin bugs should help with smaller, calico-coloured bagrada bugs, and you may be able to use sweet alyssum as part of your defence. Sweet alyssum is such a strong attractant that the crushed foliage can be used in bagrada bug traps.
With all kale pests, early intervention will make the immediate challenge easier to handle, and often results in fewer pest problems all season long. One of the great things about growing kale is that every season comes with a second chance. After your spring kale become history, you can set out vigorous young seedlings that will mature in autumn’s cooler weather.