Why Are Tiny White Insects Flying Off My Kale?

Brush against your kale plant and a cloud of tiny white insects rises into the air — this is one of the most recognisable signs of cabbage whitefly (Aleyrodes proletella), a sap-sucking pest specific to brassica crops. Cabbage whitefly is different from glasshouse whitefly and is a persistent outdoor pest that can colonise kale heavily, particularly in late summer and autumn. Understanding the lifecycle is key to managing it effectively.

What you are seeing

The flying insects you see when you disturb the plant are the adult whiteflies — tiny (1–2mm), white, moth-like insects that feed on plant sap and lay eggs on the undersides of leaves. The eggs hatch into flat, scale-like, almost transparent nymphs that also feed on the undersides of leaves. The nymphs produce sticky honeydew, which encourages sooty mould — a black fungal growth that can coat the leaves. When you look closely at the underside of affected kale leaves you will see the flat scale-like nymphs, sometimes covered in a waxy white powder, alongside egg clusters.

How damaging is cabbage whitefly?

Cabbage whitefly is more of an annoyance than a killer for established kale plants. Unlike aphids, which reproduce explosively and can rapidly overwhelm a plant, whitefly colonies grow more slowly. The most significant problems are the sooty mould that builds up on heavily infested leaves (reducing photosynthesis) and the aesthetic impact on harvested leaves — a kale plant smothered in whitefly and honeydew is unpleasant to harvest and requires thorough washing. Young plants and seedlings can be more severely affected, with heavy infestations stunting growth.

Managing cabbage whitefly

Cabbage whitefly is difficult to eliminate once established, but populations can be reduced. Insecticidal soap sprayed directly onto the undersides of leaves kills adults and nymphs on contact — repeat weekly. Yellow sticky traps hung near the plants catch flying adults and also monitor population levels. The parasitic wasp Encarsia formosa, widely used in greenhouses, does not work outdoors. Natural predators including lacewings and some parasitic wasps will attack whitefly, so avoiding broad-spectrum insecticides helps these to build up. Remove and compost old, heavily infested lower leaves to reduce the nymph population on the plant.

Washing harvested leaves

Kale harvested from whitefly-infested plants should be washed very thoroughly in cold water — the insects float off. Submerging leaves and swishing vigorously removes adults, nymphs and sooty mould effectively. Multiple washes ensure the harvest is clean. The presence of whitefly does not make the leaves unsafe to eat once properly washed.