Blackfly Damage: How to Identify and Treat

Spotting and fixing blackfly damage in your garden

June 21, 2025 | 10 min read
A close-up of blackfly on a plant stem

As a gardener and hedge cutting contractor working in Staffordshire for over 15 years, I've seen my fair share of garden pests. Among them, blackfly are particularly bothersome, especially during the warmer months. These small aphids can create big problems if not addressed promptly. In this article, I'll guide you through identifying blackfly damage and offer practical solutions to treat it.

Quick Answer

Blackfly are small, dark aphids that cluster on plant stems and leaves. Treat them by spraying with soapy water or using a hose to dislodge them. Regular checks from April to September are key.

Identifying Blackfly Damage

Blackfly, or black bean aphids, are typically found in clusters on the soft young stems of plants, such as broad beans, nasturtiums, and sunflowers. They can cause curling leaves, stunted growth, and a sooty mould appearance due to their sticky honeydew secretions.

When and Where to Look for Blackfly

In the Midlands, blackfly are most active from late spring through to early autumn. They thrive in warm, dry conditions, so you'll often spot them during our increasingly hot summers. Regular inspections from April to September are crucial. Check the undersides of leaves and the growing tips of plants, where they tend to congregate.

Month Activity Action
April - June Early infestation Begin regular checks
July - August Peak activity Treat promptly
September Declining activity Continue monitoring

Treating Blackfly

Natural Remedies

For those who prefer natural solutions, a simple mixture of water and a few drops of washing-up liquid can be effective. Spray this directly onto the affected plants. Another technique is to blast them off with a strong jet of water from a hose.

  • Use soapy water to smother and kill blackfly.
  • Blast them off with a strong water jet.
  • Introduce natural predators like ladybirds.

Encouraging Natural Predators

Ladybirds and their larvae are voracious consumers of aphids, including blackfly. Encourage these helpful insects by planting pollen-rich flowers and avoiding broad-spectrum insecticides that could harm them.

Preventing Future Infestations

Prevention is often the best cure. Regularly inspect your plants, especially young shoots and leaves. Keep your garden healthy by avoiding over-fertilisation, which can make plants more appealing to blackfly. Rotate crops, especially if you grow beans, to disrupt the lifecycle of these pests.

Frequently Asked Questions

How do I know if my plants have blackfly?

Look for clusters of small, black insects on young stems and leaves. Leaves may curl or become sticky from honeydew.

Can blackfly harm my plants permanently?

While they can cause stunted growth and damage, most plants recover well if blackfly are controlled promptly.

Are there any plants blackfly prefer?

Blackfly are particularly fond of broad beans, nasturtiums, and sunflowers, but they can appear on a variety of garden plants.

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