Plant Pests: Know Your Enemy!
Updated: Oct 26, 2020
Pests! At some point we all have to contend with them.
It's important to stress that our indoor gardens suffer far less from attack than our outdoor ones, but when bugs do appear they can spread rapidly owing to warmer conditions and the absence of any natural predators.
The good news is that our otherwise healthy plants can tolerate a pest providing they have been well tended; watered properly, fed regularly and given favourable light and temperature levels. Houseplants that are already struggling with some form of neglect aren't going to fight off an attack quite so readily, so the first line of defence is to keep your plants in tip top condition. A regular spot of houseplant maintenance should alert you to any emerging problems and in the first instance you should physically remove a pest by showering it off or dabbing it with a cotton bud soaked in alcohol.
We would always advocate for natural pest control because frankly there are too many chemicals in our homes already, so here are the key offenders and the appropriate remedies to limit or remove them.
1) Blackfly, Greenfly and Aphids.
These sap-sucking insects attack the soft tissue of a plant. Growing tips are their favourite gathering point. They excrete sticky honeydew over nearby leaves and surrounding surfaces and this residue may be your first indication of their infestation. They are easily showered off. Taking care to avoid the soil, direct a strong blast of lukewarm water at the affected areas. Repeat a few days later. An alternative is to purchase Ladybirds through the post and watch with macabre fascination as they feast on your unwanted guests bottom first!
2) Compost Gnats.
Compost Gnats or Sciarid Flies lay their eggs in the surface of your plant's soil. Their larvae are maggots that can damage the roots of seedlings. The adult flies are simply annoying whilst the maggots can be harmful. To deter them, sprinkle gravel or vermiculite over the soil surface. (Adults look for moist conditions to lay their eggs)
Bacillus Thuringiensis is their biological control.
3) Mealy Bugs.
These pests resemble fragments of cotton wool, but they are not the innocuous bits of fluff they appear! A serious attack can lead to wilting, yellowing and leaf fall. Dabbing their backs with a cotton bud soaked in vodka should destroy them, but they can be persistent, and early detection is key to treating them successfully. With a major infestation, you might want to consider composting your plant to prevent them spreading in the home.
4) Scale Insects.
These immobile insects cling to the undersides of leaves and resemble small, rusty brown discs. Their outer waxy shells protect them from liquid spray but you can destroy them with alcohol just like the Mealy Bugs. Dab their backs with a vodka soaked cotton bud.
5) Red Spider Mite.
These miniature pests are very hard to spot; not so the damage they cause! They infest the underside of leaves, sucking sap which causes yellow, mottled blotches and eventual leaf fall. Small white webbing is sometimes produced between the leaves and stems. Since they thrive in hot, dry conditions, it's best to give your plant the opposite. Sit them on a water-filled pebble tray to raise the humidity and spray and water frequently to keep the soil moist. Their biological predator is another (plant friendly) mite called Phytoseiulus Persimilis.
Thrips are tiny black insects - Thunderflies just 2mm long. Left untreated they can stunt the growth of your plant and cause silvery streaks of damage across the leaves. Use a predatory mite such as Amblyseius to treat (These eat eggs and larvae too.) Ladybirds and Lacewings are also effective predators.
Blue sticky traps can be used to catch adult Thrips, which, attracted to the blue, fly straight into them. Just like Spidermites, Thrips prefer dry conditions, so by keeping the soil moist and increasing the humidity you can create an environment that is hostile to them.
These pests resemble tiny white moths. Again they suck at the sap and excrete honeydew and prolonged infestations cause yellowing and leaf drop. A parasitic wasp named Eucarsia Formosa will make short work of a Whitefly infestation.
Safe insecticidal soap sprays can be made from naturally occurring plant oils and fats. (They are effective because the oils suffocate the insect pest without causing damage to any of their predators or adversely disrupting the food chain.)
To make a Neem oil spray, mix a litre of warm water with 1 teaspoon of organic Neem oil and a quarter teaspoon of mild liquid soap. Shake it up well and spray all affected areas - especially the undersides of leaves. A few applications of this mixture ought to be enough to treat most pest problems without having to resort to chemicals.