Cyclamen and broad mite

What you are looking at

The old leaves are fine. That is the first thing, and it is most of the diagnosis.

Everything new comes out wrong. Small, thickened, curled hard downwards at the edges, with a stiff brittle feel where a young leaf should be soft. Turn one over and the underside has a bronzed or russeted sheen, almost varnished, quite unlike the matt green it should be. The growing point clenches into a tight knot and the plant stops getting bigger.

The flowers go the same way. Buds brown and drop before opening, and the ones that make it through are streaked, one-sided or fail to expand properly.

Then you look for the cause and there is nothing there. No webbing, no black specks, no insects on the undersides, nothing that moves when the leaf is tapped. That combination, severe distortion of new growth with nothing visible causing it, is the signature.

Why you cannot see them

Broad mite is around 0.2 mm long and cyclamen mite is not much bigger. Both are translucent. A hand lens of the kind sold for reading a map will not resolve them, and even a 20x loupe shows little more than a moving speck. Anything you can comfortably see and identify on a leaf is something else.

They also hide. These mites live in the folds of the unopened growing point, deep inside the crown, pressed against tissue that has not unfurled. That is why they are hard to spray, hard to wash off and easy to carry to the next plant on a finger.

Their feeding does the damage through what they inject rather than through what they take. Saliva from a few dozen mites on a leaf primordium a millimetre across disrupts how the whole leaf develops, so the visible result is enormously out of proportion to the number of animals present.

The three-way misdiagnosis

You will reach for thrips or a virus first, as most people do, and there is a clean test for each.

Thrips leave evidence. Tap an affected leaf over a sheet of white paper and thrips fall off as dark slivers that run rather than fly. They also scatter tiny black specks of excrement, like flecks of varnish, across the leaf surface, and their stippling appears on mature leaves as readily as on new ones. Broad mite leaves no specks, drops nothing onto the paper, and never marks a leaf that was already fully expanded when it arrived.

A virus keeps going. Cut out every distorted shoot and a virused plant produces more distorted growth from whatever is left, indefinitely, because the virus is in the sap throughout. Mite damage stops once the mites do. Virus symptoms also tend to be mottling and colour breaking without much thickening, where mite damage is a change in texture and shape more than in colour.

Herbicide drift hits several unrelated plants downwind on the same day and tends to strap and twist leaves into narrow cupped shapes. A mite problem moves plant-to-plant over weeks, always by contact.

What recovery looks like

Slower than it should be, which catches people out and makes them conclude the treatment failed.

The mites attack tissue before it has expanded. A leaf that emerges distorted this week was damaged when it was too small to see, so growth keeps coming out wrong for a fortnight or more after the population has been dealt with. Judge by the third or fourth new leaf rather than the first.

Cyclamen and African violets, whose leaves all come from a single tight crown, often never look right again even when the mites are gone, because the crown itself was the thing damaged. Those two are usually best replaced. Peppers, begonias, fuchsias and ivies grow out of it once they start pushing clean growth.

What to do about it

Look at the newest leaves in the centre of every plant you buy, and refuse the ones with a clenched bronzed growing point.

Isolate anything suspect the moment you notice, and wash your hands after touching it.

Water and handle the clean plants before you touch an affected one.

Throw away a badly affected cyclamen or African violet rather than trying to rescue it.

On a plant worth keeping, cut out every distorted shoot and leaf, bagging as you go.

Introduce Amblyseius predatory mites early, and repeat two or three times a fortnight apart.

Space the plants out, drop the temperature and get air moving.

Wait for the third or fourth new leaf before deciding whether it worked.

What it gets mistaken for

Thrips leave black excrement specks, damage older leaves too, and can be shaken onto white paper.

Red spider mite webs the shoot tips and can be seen with a hand lens.

Aphids distort young growth and are plainly visible, with cast white skins and sticky honeydew left behind.

A virus goes on producing distorted growth forever and mottles the colour without hardening the leaf.

Herbicide drift arrives on one day across several unrelated plants.

Boron shortage also puckers and stunts growing points, and it shows across a whole bed of one crop grown on the same ground rather than spreading from a single plant.