Spider mites can be a menace to both outdoor and indoor plants. Their miniature size makes them practically invisible to the naked eye, so you will need a magnifying glass to spot them. This, of course, makes it also difficult, even for an experienced gardener, to detect a spider mite infestation early on. And unfortunately, one often notices their wilting and struggling plants far too late, once the damage has been already done.
So, if you suspect that your houseplants or greenhouse crops have been attacked by the little critters, read on!
This article will help you learn how to recognise the early signs of spider mites nesting on your ornamental flowers or organic veg, as well as teach you about the most effective treatments to get rid of these creatures and keep your plants safe and thriving.
Spider mites are members of the Acari family Tetranychidae. There are over 1000 species, which differ in their colour (from white to red, brown, etc.), size and habitat. These garden pests have eight legs and are often smaller than a millimetre in size. They love dry and hot conditions and feed on the sap of leaves and blossoms.
The minuscule critters have a relatively short life cycle (between 2 and 4 weeks) and can reach adulthood within 5 days. They can hibernate in the soil, plant debris and crevices in structures when cold weather sets in. This, however, doesn’t apply to protective environments, such as greenhouses or your heated home.
Once infested with these hard-to-spot destroyer pests, your hydroponic vegetable crops or houseplants may suffer all year round if not treated on time.
The pests’ rapid breeding skills and genetically passed-on resistance to pesticides are the reasons why even keen horticulturalists often feel out of depth when trying to get rid of a spider mite infestation.
Different spider mite species are attracted to different plants but almost any type of indoor-grown veggies are susceptible to their damaging activity. On that note, there are various indicators, showing that a specific plant has been affected. The specificity of the signs, again, depends on what type of spider mite species are feasting on your greens, strawberries and decorative plants.
In general, these may include:
Furthermore, badly affected plants will eventually shed their discoloured leaves. Another common denominator for a severe infestation is the typical webbing, always present on the plant, which gives the ‘spider’ name of the pesky acarid. These silken threads are visible to the naked eye, so you can’t miss them at close inspection. The mites produce and use them as a means of moving, usually upwards, from leaf to leaf.
The best way to find out if your house plants have been invaded by spider mites is to get into the habit of inspecting the stems and underside of the leaves on a regular basis. Get a magnifying glass and check for white-yellow, orange-red, black or red “specks” on the surface. These are the colours of common spider mites that can be both native or exotic to Australia.
Another way to check if two-spotted, tomato russet, bean, red-legged or broad spider mites have plagued your indoor garden is to shake the plant over a white piece of cloth or a sheet of paper. The tiny crawlies should fall and appear looking like moving specks of dust. If you get a magnifying tool, you may also notice black frass, white skin-sheddings, white larvae or light-orange eggs.
The symptoms of a spider mite infestation are also not too hard to spot if you look closely at the foliage and assess the overall state of your plants, which may look underwatered and withered.
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So, let’s explore the ways to fight a spider mite problem and save your delicious greenhouse edibles or indoor ornamentals and evergreens.
There are some biological methods that are effective in exterminating or preventing a spider mite infestation on plants. Which one you should use will depend on the size of your garden.
For instance, you can introduce a type of predatory mites (Phytoseiulus persimilis), widely available in specialised stores in Australia, to destroy a colony of spider mites and their eggs in your greenhouse. Ladybugs and praying mantis will also keep your plants safe if you place them in your garden.
Understandably, however, it doesn’t sound feasible or wise to invite any insects, even beneficial, when you are trying to kill spider mites on indoor plants. So, to keep the little crawlies at bay and protect your houseplants, you can grow pest-repellent plant varieties, such as Chrysanthemum, dill and coriander. Companion plants, of course, are more of a preventative measure and won’t do much if your entire greenhouse strawberry crop has been infested with nuisance pests.
If you are looking for a natural solution to the spider mite problem, there are a few you can try.
Note that you can treat a single houseplant, for instance, with just pure water. Wipe the leaves or wash the plant under the tap or shower to kill off any spider mites on it.
As spider mites like a dry and hot environment, raising the humidity level in your grow room or greenhouse will affect adversely their ‘well-being’. You can resort to daily misting or water-spraying, as long as the plants you grow can tolerate humid conditions and are not susceptible to fungus infections.
Not a very popular control measure but growers can also use a hand-held vacuum cleaner to remove manually the pesky pests from their plants.
If you wonder how to get rid of spider mites during flowering, there is an effective organic acaricide, which may help you in the quest. Purchase a product that contains pyrethrin from any organic garden pesticide store and read carefully the label instructions before proceeding with the application.
Derived from certain Chrysanthemum species, the substance is toxic to insects. Note, however, that beneficial insects will be also affected if you intend to use it outdoors. Furthermore, it can cause skin and respiratory reactions in people, especially kids, so keep the product out of children’s reach and use it with caution.
A mixture of 2% rosemary oil and water can also reap successful results with moderate infestations.
The most effective chemical insecticides that can be useful against spider mites, as well, are two synthetic pyrethroid substances, called permethrin and bifenthrin. Both match the properties of the above-mentioned natural pyrethrin but differ in their susceptibility to UV light and changes in pH.
Again, their application may be contraindicated indoors if you have young children or allergic family members but can be used to treat plants grown in a greenhouse. Apply carefully and bear in mind that spider mites may become resistant to the product over time, due to their short life cycle, which prompts growers to repeat treatments excessively.
Surely, prevention is always better than cure, so here’s what you should know, in order to keep your plants spider mite free.
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