Black fly on plants? Blackfly is a species that will actively destroy your plants, but can you get rid of blackfly without damaging your plants? Fortunately, there are many natural ways that you can remove blackflies without causing any harm to your plants. Furthermore, there are things gardeners can do to prevent an infestation in the first place. Knowing how to control the blackfly population in your garden is imperative if you want it to remain healthy and happy. In this short guide, we will be detailing everything you need to know.

Aphid Infested Plant
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What Are Blackfly?

Blackfly are small, sap-sucking insects from the aphid family, notorious among gardeners and farmers for their destructive impact on plants. Characterised by their dark colouration, which can range from black to dark green or brown, they are most commonly recognised in their infestation of the broad bean plant, hence the name ‘black bean aphid’. These pests are particularly problematic because they not only drain the vital fluids from the plants, causing wilting and stunted growth but also excrete a sticky substance known as honeydew. This secretion can lead to the growth of sooty mould, further impairing photosynthesis and plant health.

How Fast Do Blackfly Spread?

One of the most alarming characteristics of blackfly is their reproductive capability. Female blackflies can give birth to live young without the need for male fertilisation, a process known as parthenogenesis. This allows their population to explode during the growing season, with each female potentially adding hundreds of offspring to the colony. Beyond physical damage, blackflies are also vectors for plant viruses. Once a plant is infected, viruses can spread rapidly, compromising the health of the entire garden or crop.

How To Get Rid Of Blackfly Safely

If you have recently noticed more and more blackflies appearing in your garden, it is essential that you handle the problem sooner rather than later. The longer you leave it, the more problematic it will become and the more likely it will be that your plants become infected.

1 – Home-Made Aphid Spray

  • 1 teaspoon of mild liquid soap (like castile soap)
  • 1 litre of water
  • Mix and spray directly onto the aphids and affected parts of the plant.

When using homemade sprays, always test a small area of the plant first to ensure it does not cause damage. Apply during cooler parts of the day to avoid burning the plants, and reapply every few days or after rain.

2 – Water

You can simply wash the blackfly away but this is something that you will need to keep on top of. It is a good idea to rinse them off your plants at least every couple of days until the infestation clears. However, you should also keep in mind that a relatively strong jet of water is needed so this may only be suitable for less delicate plants.

3 – Essential Oils

While essential oils may come from plants, they can also help your plants when there is an outbreak of blackflies. Some of the best options include clove oil, thyme, rosemary and peppermint; these are all incredibly strong.

You should place between three and four drops into a spray bottle and finish off the solution with water. This can then be sprayed onto the affected plants and the blackfly, along with their eggs will be killed. Make sure that you get the whole of the plant including the undersides of the leaves.

4 – Bird Water Bath

One of the best natural methods of removing blackfly is to encourage predators. Birds will make a meal of an infestation but they first need to be encouraged to your garden. Leaving out a bird feeder or a bird water bath (Amazon link – opens in a new tab) will bring more attention and once they spot those blackfly, they’ll soon gobble the lot.

5 – Squash Them

It may seem obvious, but one of the most effective ways to remove blackflies is to simply pick them off the plants and squash them between the thumb and forefinger. Of course, this will take a little longer than other methods and you’ll have to be patient, especially if there is a larger presence, but it can be incredibly effective.

Blackfly Infestation on a Tomato Plant
Blackfly Infestation on a Tomato Plant

What Do Blackfly Eat?

These aphids feed on plant sap, particularly favouring young, tender growth. As they feed, they excrete a sticky substance called honeydew. This sugary residue attracts sooty mould fungi, which coat the leaves and stems, hindering photosynthesis and weakening the plant. While blackfly can target a wide range of plants, some of their preferred hosts include:

  • Cucumbers: These garden staples are particularly vulnerable to blackfly, which can stunt their growth and reduce yield.
  • Strawberries: The sweet fruits and tender leaves of strawberries are attractive to blackfly, potentially ruining the harvest.
  • Tomatoes: Aphids can quickly colonize tomato plants, spreading viruses and attracting sooty mould.
  • Tulips: Even ornamental plants like tulips are not immune, with blackfly affecting both the aesthetics and health of the blooms.
  • Raspberries: These bushes can become overrun with aphids, leading to poor fruit development and fungal issues.
  • Dahlias: The lush foliage and vibrant flowers of dahlias can be marred by the presence of blackfly.
  • Runner Beans: These climbing plants can be heavily impacted, with aphids affecting both the leaves and the beans themselves.

How to Prevent Blackfly?

Preventing blackfly infestations in your garden involves a combination of proactive measures and vigilant monitoring. Here are some strategies to help keep these pests at bay:

  • Encourage Beneficial Insects: Introduce or attract natural predators of blackfly into your garden, such as ladybirds (ladybugs), lacewings, and hoverflies. These beneficial insects can significantly reduce blackfly populations.
  • Use Companion Planting: Planting certain plants that repel aphids, like marigolds, garlic, chives, and nasturtiums, can help deter blackfly from settling on your crops.
  • Regular Inspection: Check your plants frequently for early signs of blackfly infestation, especially on the undersides of leaves and on new growth. Early detection is key to preventing a full-blown infestation.
  • Maintain Plant Health: Keep your plants healthy and stress-free, as strong plants are less susceptible to aphid attacks. Ensure they have the right nutrients, water, and sunlight.
  • Water Spray: A strong jet of water can dislodge aphids from plants. This can be an effective immediate remedy, but it may need to be repeated since it doesn’t prevent blackfly from returning.
  • Prune Infested Growth: If you notice blackfly on a particular part of a plant, prune that section away to prevent the spread. Dispose of the infested plant material securely.
  • Reflective Mulches: Using reflective mulch around the base of plants can disorient aphids and deter them from landing.
  • Sticky Traps: Yellow sticky traps can catch flying aphids and reduce their numbers.


Blackflies are a species of aphid, a small, flying insect that loves to feed on the sap from your favourite garden plants. While they are a part of the UK’s wildlife, and won’t ever be completely eradicated, there are ways that you can control them and prevent them from damaging your plants. However, it is important to choose methods that will not cause further damage to your plants, that is what we are trying to avoid in the first instance. Using essential oils, encouraging predators and simply squashing the bugs between your fingers are all viable methods. Furthermore, it is imperative that you take preventative action to avoid future infestations.

Garden Doctor Tips

Garden Doctor Trev

“Dilute a few drops of peppermint oil in a spray bottle and coat your plants!”

“Give your ants something sweet away from your plants so they are not tempted to farm the aphids!”

“Be careful if washing down your plants, some plants are extremely delicate and won’t cope too well!”

“Having a good variety of plants in your garden is a good way to keep down the number of aphids as it increases the number of predators too!”

Frequently Asked Questions

How do you get rid of black flies naturally?

Black flies are common pests that can be frustrating and difficult to kill. The best way is by using peppermint oil, which will repel the insects from your plants without any harsh chemicals or toxins. Dilute a few drops in water and spray liberally.

How do you get rid of black aphids?

You will see that many people recommend using neem oil or other horticultural oils. These are not necessarily good for the environment and in fact, neem oil is banned in the UK. We recommend using diluted natural peppermint essential oil. 

How do I keep blackfly off my runner beans?

The best way to keep blackflies off your runner beans is to dilute a few drops of peppermint essential oil and spray them over your beans. Remember to spray the underside of the leaves too!


Trevor Wright is not just a seasoned horticulturist; he’s the esteemed Garden Doctor. With a BSc in Horticulture and years of hands-on experience in the soil, Trevor has become a trusted mentor for all things gardening. As the founder of Garden Doctor, he’s committed to clarifying the intricacies of gardening, offering straightforward advice that’s rooted in years of practice. His writing is a garden of how-tos, savvy insights, and comprehensive guides that enable individuals to nurture and grow their garden dreams. When he’s not knee-deep in garden beds, Trevor is at his keyboard passing on his green-thumbed wisdom to budding gardeners, ensuring that the legacy of sustainable and joyful gardening blossoms far and wide.

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