Citronella and Tea Tree for Horses: Grooming Actives Against Fly Bother

Citronella, lemongrass, eucalyptus and tea tree are cleansing, scent-based actives that make a freshly washed coat smell far less appealing to flies and midges — for a while, anyway. They're not insecticides, and they won't replace rugs, sprays and good stable hygiene. What they do offer is a useful layer of summer comfort, built right into the bath itself.

Citronella, lemongrass, eucalyptus and tea tree are the botanical actives you'll most often meet in insect-repelling horse washes, and for good reason: flies and midges are put off by their sharp, volatile scent, and all four have a long history of use in skin-friendly grooming products. Used in a proper wash such as repel-oil-shampoo, they help make a horse smell and feel less inviting to biting insects during a bath, while tea tree in particular leaves the coat feeling clean rather than greasy. None of this makes a shampoo a substitute for a fly rug, a repellent spray, or good stable hygiene — it's one useful layer in a wider summer routine, not a standalone fix.

Why these particular botanicals turn flies away

Citronella oil is distilled from lemongrass-family grasses and has been used for well over a century as an insect deterrent, in everything from candles to skin lotions. Its strong citrus-and-grass aroma masks the scent cues flies and midges use to find a host, which is why it turns up so often alongside actual lemongrass oil in grooming products aimed at summer use. Eucalyptus works on a similar principle: its sharp, medicinal note is pleasant to us but disorienting to small flying insects, and it has a long folk history as a natural fly deterrent around stables and paddocks.

Tea tree oil brings something slightly different to the blend. Rather than being purely about smell, it's prized in grooming for its light, almost squeaky-clean feel on the coat, and its long association with keeping skin and hair looking fresh. In a wash formulation it pairs well with citronella and lemongrass because it rounds out the fragrance and adds to the sense that the coat has been properly cleansed, not just doused in something insects dislike.

What a repelling wash can realistically do

It's worth being honest about what these ingredients are and aren't. A citronella-and-tea-tree shampoo is a grooming aid, not a systemic insecticide and not a registered pesticide. It won't kill flies, and it won't eliminate insect activity around a horse for a set number of hours the way a chemical spray-on repellent might claim to. What it does is leave a scent trail on the coat that many horse owners find genuinely reduces bother during and shortly after a wash — useful on a hot, fly-heavy afternoon, or for getting a horse comfortable before turnout in a buggy paddock.

Because the effect comes from a topical scent rather than a lasting chemical barrier, it fades. Sweat, rain, rolling in the field and simple time will all shorten how long a horse smells of citronella and tea tree after a bath. Sensible expectations matter here: use the wash as one part of a summer fly-management plan alongside rugs, repellent sprays formulated for longer wear, muck management, and shade — not as the only line of defence.

Cleansing and insect-bothering in one step

The appeal of building citronella, lemongrass, eucalyptus and tea tree into a wash rather than a separate spray is efficiency. A summer bath is already on the to-do list in hot weather, particularly for a horse in hard work who is sweating and needs regular washing down. Formulating that wash with insect-repelling botanicals means the fly-deterrent step happens at the same time as the actual cleaning, rather than as an extra product and an extra ten minutes. Repel Oil Shampoo is built around exactly this combination — citronella, lemongrass, eucalyptus and tea tree in one cleansing formula — so the coat comes out of the wash smelling sharp and citrusy rather than sweet, which is precisely the scent profile that tends to put flies off in the short term.

Want the technique right — wetting, working the shampoo through, and rinsing thoroughly so nothing dries tacky on the coat? It's worth following how to wash a horse step by step rather than assuming any bath will do. A rushed rinse can leave residue that attracts dust and undoes some of the freshness you were after.

Building it into a summer routine

On its own, one bath a week rarely does much against a serious fly problem. The horses who seem most comfortable through summer tend to have a routine: rugs and fly masks fitted early in the season, a repellent spray topped up daily, and a wash day that includes an insect-deterrent shampoo rather than a plain one. Our guide to summer fly grooming sets out that fuller routine in more detail, including how to time washing around turnout so the coat is at its freshest when flies are at their worst — typically dawn and dusk.

Grooming for insect bother isn't limited to leisure horses either. Competition horses standing at a busy summer event, tied to a trailer for hours with limited shade, are arguably under more pressure from flies than one turned out in an open field. Our piece on eventing grooming: the three phases touches on keeping a horse comfortable and settled between phases, and a citronella-and-tea-tree wash the evening before or morning of competition is a small, sensible addition to that kind of prep.

When it is not just flies — call the vet

There's an important line to draw here. A horse rubbing its mane and tail raw, or one that reacts badly to midge bites with hives, weeping skin, or hair loss along the topline, may be dealing with sweet itch or another allergic response rather than simple everyday fly bother. Grooming products, however well formulated, are cosmetic aids — they clean, they freshen, and they can make a horse smell less appealing to insects for a while. They're not medicated treatments, and they won't resolve an allergic skin condition. If you suspect sweet itch, genuine insect-bite hypersensitivity, or any skin reaction beyond ordinary irritation, that's a conversation for your vet, not something to manage through shampoo choice alone.

The same caution applies to any horse showing signs of mite infestation, mud fever, or unexplained sores — these need proper veterinary diagnosis. Where skin is simply a little dry or mildly irritated from heat, sweat and general insect activity, a soothing cosmetic balm can help the coat and skin feel more comfortable as part of aftercare. But it's not a treatment for disease, and it should never substitute for veterinary attention when something looks genuinely wrong.

The bottom line

Citronella, lemongrass, eucalyptus and tea tree earn their place in summer grooming because they combine two jobs a horse owner already needs done — washing the coat and making it less pleasant for flies to linger on — into a single, pleasant-smelling step. Treat the result as a genuine but time-limited aid, pair it with the rest of a proper fly-management routine, and keep an eye out for anything that looks like more than ordinary bother. That's where grooming stops and veterinary care needs to start.