Why is my kale covered in grey powdery aphids?

This is the aphid that ruins winter brassicas. It is not the green one people are used to: it is grey, coated in a white waxy powder that sheds water and sprays alike, and it colonises the growing tip and the inside of sprout buttons where it is protected from weather, predators and anything you might apply.

Step by step

1. Identify it properly.Dense grey colonies with a mealy white waxy bloom, packed on leaf undersides and clustered in the growing point. Leaves above them are distorted, yellow-mottled and curled. The wax is what distinguishes it from ordinary green aphids.
2. Check the growing points weekly from midsummer.Catching a colony while it is confined to one tip is the difference between cutting out a shoot and losing the plant. The tip is where they start.
3. Cut out and bin infested growing points.Do not just squash them. Remove the affected tip or leaves entirely and put them in the bin, not on the compost heap.
4. Jet the colonies off with water.A strong spray from a hose knocks colonies off the leaves and they largely fail to climb back. It has to be repeated every few days, but it works and it costs nothing.
5. Squash small colonies by hand.On leaf undersides, a gloved finger and thumb deals with an early colony in seconds. Check under every leaf while you are there.
6. Strip and bin badly infested lower leaves.It reduces the population and improves airflow. Do not strip the plant bare — leave the healthy upper growth.
7. Clear old brassica stumps and debris in spring.This is the important preventive step. The aphid overwinters on brassica plants and stumps left on the plot, and moves onto the new crop from them. Clearing the old bed properly breaks the cycle.
8. Encourage predators.Ladybirds, hoverfly larvae, lacewings and parasitic wasps all take mealy cabbage aphid. Flowers near the vegetable bed and a tolerance for a few aphids early in the season is what keeps them present when you need them.
9. Net with fine insect mesh from planting.Insect mesh fine enough for cabbage white also excludes winged aphids arriving in summer, so the same cover does two jobs. It has to go on before they arrive.

Tips

• Sprouts are the worst affected because the aphids get down inside the buttons, where nothing reaches them and where you find them at the sink in December.
• Kale and cavolo nero recover well if the growing point is saved — cut out the tip and the plant produces side shoots.
• Wash harvested kale and sprouts in salted water to bring out anything hiding in the crevices.
• Aphid numbers explode in warm dry late summers. A wet August genuinely reduces the problem.
• Do not spray a plant in flower or covered in ladybird larvae — you will remove the predators that were about to solve it for you.

Common mistakes

• Waiting until the plant is covered — Once colonies are inside the growing point and the sprout buttons, nothing you apply reaches them. Weekly checks and early removal is the whole strategy.
• Leaving last year's brassica stumps standing — They carry the population through winter and reinfect the new crop in spring. Clearing them is the single most effective preventive measure.
• Composting infested material on a cool heap — It survives and returns. Bin it or use council green waste.
• Relying on a spray — The waxy coating sheds liquid, and the colonies sit in protected crevices. Physical removal and hygiene work far better.

Questions people ask