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The five most common insects to invade your hydroponic garden

A lot of work goes into producing a healthy, high-yielding, hydroponic crop. It is both an art form and a science, and the more you do it, the more your intuition and judgement tells you what the plants you’re growing need to thrive.

But no matter how much experience you have, or how many successful crops you’ve produced, there’s always something waiting in the wings to thwart your best efforts. So, let your guard down at your peril, because if you do, you may just find a range of pesky critters taking up residence in your indoor garden.

Check out our range of insecticides here!

Although there are a large range of insects that blight crops grown indoors and out, some are more prolific than others. So, with that in mind, we’re looking at the top five you’re likely to encounter in hydroponic growing.

Spider mites

Spider mites are arachnids; relatives of spiders, ticks and scorpions. They are renowned for causing havoc in indoor and outdoor gardens. Measuring less than a millimetre in length, they can be very difficult to see, despite their red colour. Spider mites tend to live in colonies on the underside of leaves, and this is where they do their most damage.

Spider mites are a problem because they feed by making a hole in the leaf and sucking out the plant fluid. If left untreated, the leaves turn yellow, dry up and drop off.

Spider mites are very prolific breeders, so left unchecked, populations can build up to significant levels before plant damaged becomes apparent, which is a real headache for growers.

How to tell if you have spider mites

Establishing if you have spider mites can take a bit of detective work. Firstly, like their larger cousin the spider, they spin webs, so look for any webbing on the underside of the leaf. Take a magnifying glass and examine the leaf too, and if you have a heavy infestation, you’ll likely see them moving around.

Another test is to take a tissue and carefully wipe on the underside of the leaf. If this yields any blood, chances are you have spider mites.


Thrips is the name given to an order of small, winged insects, many of which feed by sucking sap from leaves and flowers. Unfortunately for hydroponic growers, thrips thrive inside.

Adult thrips are about 2mm in length and have two pairs of strap-like wings which are fringed with hairs. Because of this, they can fly or jump between plants, meaning they can soon infect an entire crop.

The most damaging thrip species to indoor growers is generally regarded to be the Western flower thrip. Although a North American species, it has been present in the UK since the mid-1980s. It attacks a range of plants causing silvering of the leaves, stunted growth, flecking and premature deterioration of flowers.

How to tell if you have thrips

Certain species of thrip will be visible with the naked eye as small brown specs, although different species do vary in colour. Unlike spider mites, there is no webbing. Another way is to shake the foliage over a white sheet of paper and then examine with a magnifying glass. If thrips are present, they should be easily visible.


Aphids will be familiar to practically every grower and non-grower alike. They are tiny, soft-bodied insects that can appear in a range of colours, from black and brown to pink, but are generally are mostly commonly green. They have pear-shaped bodies and most species have two short tubes, called cornicles, projecting from their hind end.

One interesting fact about aphids is that although most species are wingless, adults can develop wings when populations are high and food is scarce, to enable the population to disperse, travel to new plants and start a new colony.

Aphids feed on the plant juices, taking it from every part of the plant – stems, leaves, buds, flowers, fruits and roots, depending on plant species. Damage generally includes misshapen or stunted, yellow leaves; flower and fruits distorted or deformed and; gall formation on leaves or roots.

How to tell if you have aphids

Generally, aphids are visible to the naked eye. And like other pests, they tend to congregate on the underside of leaves and then move about the plant to feed. Another tell-tale sign is sticky leaves or stems. This occurs due to ‘honeydew’, a sugary substance excreted by the aphids as waste.

Honeydew can itself cause other problems. Other insects such as ants and ladybirds are attracted to it to feed, and it can encourage sooty mould to develop, so these are secondary signs of aphids too.


Whiteflies are pretty easy to identify. They truly live up to their name. A close relative of aphids and mealybugs, they are white flies that look triangular in shape and can often be found in clusters on the underside of leaves.

Whiteflies can quickly overwhelm a plant, sucking it dry and rendering it unable to carry out photosynthesis. The leaves soon turn yellow and become misshapen and stunted.

Like aphids, whiteflies produce honeydew and it is a sign that they have been feeding for several days.

How to tell if you have whitefly

Whitefly are among the easiest pests to identify because they are visible to the naked eye and often, when a plant is disturbed, will fly off in a swarm. But if you are unsure, check the underside of leaves, especially near the veins, and feel the leaf surface for honeydew. Also look out for eggs, which vary between pale yellow and brown in colour. The female lays around 400 and young start sucking the plant juices as soon as they hatch.

Fungus Gnats

Adult fungus gnats grow up to between 2mm and 8mm so are easily visible with the naked eye. Some species are exceptionally hardy, being able to tolerate cold conditions due to antifreeze proteins. Adult gnats are harmless to healthy plants, it is the larvae that cause the problems. The larvae feed on the roots of a plant and the feeder roots, which slows growth and opens up the plant to bacterial infection.

The presence of fungus gnats can be a sign of over-watering. The gnats feed on roots which have been sat in water too long and are thus beginning to rot. Or they are maybe attracted to fungus feeding on the saturated top soil, so if you find you have fungus gnats, it is a good idea to check your watering routine.

How to tell if you have fungus gnats

Due to their size, fungus gnats are easy to see and identify. Most are weak flyers and are often seen walking on plants and soil rather than flying. They are typical gnat size, shape and colour, so if you see this type of insect on your plants, chances are they’re fungus gnats.

Controlling pests

Control comes in two forms – chemical or biological.

Chemical control, as the name suggests, is the application of various insecticide chemicals on to the plant to kill and pests. These may come in the form of sprays or plant washes, organic and non-organic.

Biological control involves using beneficial predators, such as nematodes, to hunt down and eat the pests.

Both have advantages and disadvantages. Chemical control, for example, is low cost, effective and quick acting. However, in their non-selective form, they can be toxic to other organisms beyond the pest species, including those that are useful. This is why chemical and biological methods are rarely used together.

Long term use of chemical pesticides can cause resistance too, which is a huge problem for farmers and growers all over the world.

Biological methods have several advantages. Firstly, they tend to be effective over the long term as pests cannot become immune to being eaten! It is also a very targeted approach, with only the pest species being affected.

However, it has disadvantages too. Firstly, the species introduced to kill the pest will never fully get rid of it. This is because it depends on it to live, so knows that if it wipes that pest out, it too will die. Also, biological control can only be applied once the pest is there, not before, therefore it is likely the grower will have already experienced a level of crop damage before introducing the biological solution.

Whichever method you use, it is essential you choose the right products for the job. Once damage has been detected, ensure you prune all the dead or discoloured leaves from the plants before application, and dispose of these thoroughly, and not on the compost heap.

Managing your grow room and keeping a close eye on your plants is the best way to prevent, identify and treat insect invasions, so be sure to keep vigilante. And if you do spy any symptoms of these pests or any others, go to our Pest Controlpage to find the right product, or get in touch for advice on what to do next.

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