Citrus mites

a bronze, rust-brown or silvery sheen spreading smoothly over the skin of the fruit and the leaves — as if the fruit has been lightly dusted or 'sun-tanned' all over. The fruit is not rotten and is still good to eat, but the colour is spoiled and buyers pay less for it.

fine pale speckles or 'stippling' — as if someone sprinkled pale pepper or dust across the leaf — turning it dull and bronze. Look for fine silky webbing on the undersides of leaves and where a leaf touches a fruit, then yellowing and early leaf and fruit drop when it gets bad.

— you need a cheap hand lens (a 10-times magnifier). Rust mites look like a faint pale-yellow 'dust' or fog creeping on the green fruit. Spider mites are moving specks the size of fine sand — brick-red, or pale-green with two dark spots — mostly on the underside of leaves, in among their webbing. Tip: tap a leaf over a sheet of white paper and watch for tiny specks that crawl.

wind-scar or sunburn (rough, corky patches only where branches rubbed, or damage only on the sun-facing side — rust-mite bronzing is smooth and even, all over the fruit); or a plain nutrient shortage (leaves go an even yellow with no tiny specks and no webbing, and the paper-tap test shows nothing crawling).

start checking from the time the little fruits have set and are growing, and keep it up right through to harvest — the whole fruit-growing and ripening season. Look once a week, and step up to twice a week during any hot, dry, dusty, rainless spell — that is exactly the weather mites love. Carry your hand lens every time.

walk a big 'W' across the orchard so you cover all four corners and the middle — and check the dusty edge rows and roadside trees first, because mites build up there first. Make about 10 stops. At each tree, eye 5 fruit and turn over about 10 leaves, checking the undersides with your lens for mites, stippling and webbing.

the moment you see bronzing or silvering starting on the fruit of even 1 in 10 trees, treat those trees now. On the fruit the scar is permanent and spreads fast, so waiting straight away costs you the crop's grade.

if you find live mites with fresh stippling or webbing on about 2–3 of every 10 trees, and the numbers are higher than your last check, act now. Old speckling with no live mites under the lens is a past attack — don't spray for that.

water the trees well so they are not drought-stressed (thirsty, stressed trees flare up with mites), and knock down the dust that shelters them — wet the orchard roads, keep a grass strip or mulch along the edges, slow down vehicles, and in dry spells hose plain water over the leaves to wash dust and mites off.

the worst mistake is spraying a broad-spectrum insecticide (a poison that kills many kinds of insect) on a fixed calendar. It wipes out the tiny predator mites and ladybirds that normally keep mites down, and the mites then flare back far worse. Scout and spray only when you actually find them, never by the calendar.

predator mites, lacewings and ladybird beetles eat pest mites and usually hold them below damage level when you don't poison them, so conserve them. A hard jet of plain water onto the leaf undersides knocks spider mites and their dust straight off — cheap, safe, and it buys you time.

only at threshold, spot-treat the affected trees with a horticultural mineral oil (a light spray oil that smothers the mites) or a selective acaricide (a mite-killer chosen to spare the predators — 'acaricide' just means a spray that kills mites). Wet the leaf undersides and the whole fruit thoroughly, or you miss them. Safety: cover your skin, eyes, nose and mouth; spray in the cool of morning or evening with the wind behind your back; keep it off food, water, children, animals and bees; do not spray oil in the heat of the day or on a thirsty tree (it will scorch the leaves and fruit); wait out the pre-harvest interval — the number of days you must leave between spraying and picking the fruit — before you pick; and wash yourself and your clothes afterwards. Resistance: mites get used to a spray very fast, so rotate to a different chemical group each time and never use the same mite-killer twice in a row.

if mites carry on after a spray, don't just repeat the same product — switch to a different chemical group, check your coverage (undersides and fruit), and make sure dust and water-stress aren't still feeding them. If the fruit is already bronzed all over, accept that this season's fruit is downgraded — the russet will not wash off or heal — so pick and sell it as juice or lower-grade fruit, and put your effort into saving the leaves and the tree: stop the broad poisons so the predators come back, and fix the watering and dust now so next season starts with low numbers.