Spider mite spray for plants: inspect under the leaves
Updated: October 2026
Your houseplant or greenhouse cucumber develops fine pale mottling, so you reach for a spider mite spray for plants and wet the upper leaves. That can miss the pest. Glasshouse red spider mite usually feeds and lays eggs on the lower leaf surface. This guide follows Royal Horticultural Society advice, then the one plant soap in the [mite spray comparison](/hub/pest-control/mite-spray). It is not a guide to mattress aerosols or poultry products. Verify the current UK authorisation and follow the physical label for the crop.
Your houseplant or greenhouse cucumber develops fine pale mottling, so you reach for a spider mite spray for plants and wet the upper leaves. That can miss the pest.
Your houseplant or greenhouse cucumber develops fine pale mottling, so you reach for a spider mite spray for plants and wet the upper leaves. That can miss the pest. Glasshouse red spider mite usually feeds and lays eggs on the lower leaf surface. This guide follows Royal Horticultural Society advice, then the one plant soap in the mite spray comparison. It is not a guide to mattress aerosols or poultry products. Verify the current UK authorisation and follow the physical label for the crop.
Our top picks
| Badge | Product | Host | Named active | Authorisation | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  READY STEADY DEFEND READY STEADY DEFEND 1 L plant soap | Red spider mite on plants | Potassium salts and soya oils | No MAPP number in the file | 8.0 | about £14.99 | View offer |
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The mite under the leaf
Despite its common name, glasshouse red spider mite is often yellowish-green in spring and summer, with two darker patches. Adults are tiny, up to about 1 mm, so the first sign may be pale speckling on the upper leaf. Turn the leaf over. Mites, eggs, shed skins and webbing underneath make the diagnosis more convincing than yellowing alone.
Glasshouse red spider mite, often called two-spotted spider mite, is not fruit-tree red spider mite on apple and plum. A biological control for the glasshouse pest does not control the fruit-tree mite. Nutrient problems, drought and thrips can also mark leaves, so identify before treating. A contact liquid has to reach the sheltering mites. Spraying the upper surface until it runs off leaves the underside dry.
Humidity and a predatory mite
Hot, dry, crowded glasshouses favour glasshouse red spider mite. The RHS recommends raising humidity and syringing plants where the plant tolerates it. Humidity alone does not control an established infestation. Overwatering the compost is not the same as humidity around the foliage.
Phytoseiulus persimilis is a predatory mite released onto infested plants. It needs suitable temperature and humidity, and it works best before the plant is overwhelmed. Incompatible pesticides can kill the predator. If you add a contact spray, confirm the crop, reach the lower leaf surface and inspect again at the label interval. The how to use mite spray guide separates a label-led repeat from spraying again because the first treatment dried.
The one plant soap in this set
READY STEADY DEFEND is the only retained listing aimed at spider mites on plants. It is £14.99 for a listed 1 litre, covering indoor and outdoor plants, including fruit, vegetables, ornamentals and houseplants. The bullets name potassium salts and soya oils, plus red spider mite, two-spotted spider mite, aphids and whiteflies. That makes it the relevant type here. It does not prove every listed crop use is authorised.
The item-form field says aerosol, while reviewers describe a trigger or pump. Some texts discuss 500 ml beside this 1 litre listing. Check the delivered pack. One cucumber grower reports improvement after spraying beneath the leaves. Others say mites returned after the liquid dried, mini roses worsened, or a pepper treatment leaked and failed. “Reapply as needed” and “until harvest” are seller bullets, not a universal interval. Do not use the household Zero In aerosols. Their bullets concern mattresses, frames and furnishings. Why the rows cannot be swapped is in the mite spray buying guide.
A MAPP number, or you cannot verify the use
The Health and Safety Executive says plant-protection products used in gardens must be authorised. A MAPP number lets you search the HSE garden database and compare the authorised uses with the label. If the listing hides the number, ask for a readable photograph. Check the number, not only the product name, because permissions change.
The retained READY STEADY DEFEND file shows no MAPP number. That does not prove the bottle is unauthorised. The listing evidence is insufficient. “Natural”, “soap” or named oils do not make an application permissible. Safer’s Insecticidal Soap, MAPP 06573, appears in the HSE database with an expiry of 30 June 2018. A historical number or a similarly named product cannot authorise a different bottle today. “Until harvest” is not a crop assessment. The best mite spray by job does not waive that gap.
Common questions
What does glasshouse red spider mite look like?
In spring and summer it is commonly yellowish-green with two darker patches, not bright red. Look for fine pale mottling above and mites, eggs, skins or webbing beneath the leaf. Adults reach about 1 mm.
Does raising humidity clear spider mites?
No. Higher humidity and syringing can reduce risk where suitable for the plant, but the RHS says humidity alone does not control an infestation. Combine prevention with identification, monitoring and an appropriate control.
What is Phytoseiulus used for?
Phytoseiulus persimilis is a predatory mite used against glasshouse red spider mite on infested plants. It needs suitable conditions and does not control fruit-tree red spider mite on apple or plum.
What is in the plant spray compared here?
The READY STEADY DEFEND bullets name potassium salts and soya oils. The retained listing says 1 litre, although the form field conflicts with trigger-bottle reviews and some reviews refer to 500 ml.
Why does a missing MAPP number matter?
Without a MAPP number, you cannot check the product’s current UK authorisation and permitted uses in the HSE garden database. The number may be on the delivered label, so request clear evidence before buying or applying.
Does “until harvest” prove food-crop approval?
No. In this file it is a seller bullet, not a displayed authorisation record. Verify the MAPP number, crop and harvest directions on the current label before treating an edible plant.
Can a bed-bug aerosol be used on plants?
Not unless its authorised label specifically includes that plant use. The retained Zero In aerosols are aimed at indoor mattresses, frames and furnishings, so they are the wrong row for a crop or houseplant.
Related pages
Sources
Public UK sources from the research digest, last checked on 15.10.2026.
- Cambridge University Hospitals — Dust mites in your home (retrieved 15.10.2026)
- Allergy UK — House dust mite allergy factsheet (retrieved 15.10.2026)
- HSE — Regulated biocides (retrieved 15.10.2026)
- HSE — Using biocides (retrieved 15.10.2026)
- HSE — Pesticides in the garden and home (retrieved 15.10.2026)
- RHS — Glasshouse red spider mite (retrieved 15.10.2026)
- GOV.UK — Poultry welfare recommendations (retrieved 15.10.2026)
- BPCA — Secondary infestations from birds (retrieved 15.10.2026)