Broad Mites

Broad mites are the pest people chase for two months while treating something else. They are roughly a fifth the size of a spider mite, effectively invisible at the magnification most growers own, and the damage they cause looks exactly like several much more common problems.

If you have been adjusting pH, changing nutrients and moving the light for weeks and the new growth keeps coming in wrong, read this page carefully.

What you are seeing#

The damage is always on new growth. Older leaves lower down stay normal, which is the single most useful clue and the one that rules out most deficiencies.

New leaves emerge twisted, curled upward at the edges, and narrower than they should be. They often look wet or lacquered, with a distinctive glossy sheen that catches the light. Growth tips may blister, go bronze or brown, and stop developing entirely.

In flower, buds stop filling and the sugar leaves around them twist and brown. A plant that was fine in week three can look like it has been scorched by week six.

You will not see the mite. This is the defining feature. At 30x through a loupe you will see nothing at all. They live on the newest tissue, in the growing tips and tight between emerging leaves, and they are translucent. Confirming them visually requires 100x or more, which almost nobody has.

So diagnosis is by pattern, not by sighting.

How to tell it apart#

The pattern that points at broad mites rather than anything else:

It is only the new growth. A deficiency moves through the plant. Zinc or calcium problems show on multiple leaf ages and often follow the veins. Broad mite damage is confined to whatever the plant has produced most recently, and older leaves stay clean.

The glossy look. Zinc deficiency twists new growth and shortens the gaps between nodes, but the leaves look dull and chlorotic rather than wet and shiny.

It does not respond to feeding changes. If you have corrected pH, flushed, and adjusted nutrients with no improvement over two weeks, stop treating it as a deficiency.

It does not respond to environment changes. Wind burn and light burn both twist and crisp new growth, and both improve within days of moving the fan or raising the light. Broad mite damage keeps getting worse.

It spreads to neighbors. A deficiency affects the plant with the problem. Broad mites move, and the plant next to it starts showing the same thing a week later.

Russet mites are the closest match and need their own page. Broadly: broad mites hit the growing tips and make leaves glossy and twisted; russet mites work up from the bottom of the plant and leave leaves dull, brittle and bronzed.

Why it happens#

They almost always arrive on a plant. A clone, a cutting from a friend, a plant brought in from outside, or an infested plant from a shop.

They do not appear spontaneously in a clean indoor room. If you have them, something came in, which is worth knowing because it tells you what to change afterward.

Warm conditions speed them up considerably. A tent in the high seventies with a dense canopy is ideal for them.

How to fix it#

Treatment is harder than for spider mites because you cannot see progress, which means you must run the full schedule on faith.

1. Isolate immediately if you can, and stop moving between plants without washing your hands and changing your shirt.
2. Remove the worst growth. Badly twisted tips are not going to recover and they hold the highest mite population. Bag them, carry them out.
3. Raise the temperature deliberately, if your plants can take it. Broad mites are unusually heat sensitive. Several days at 95 to 100F will suppress them significantly, though it stresses the plant and is not an option in flower.
4. Treat every plant, every 3 days, for at least 3 weeks. In vegetative growth: insecticidal soap, or a light horticultural oil, applied until dripping, concentrating on growing tips and the undersides of new leaves. Coverage is everything.
5. Rotate products between applications. Broad mites develop resistance quickly, and the same product four times is how a treatment stops working halfway through.
6. In flower, do not spray oils. Past about week two, oil on buds traps moisture, invites rot and ruins the taste. Predatory mites, specifically Amblyseius swirskii or Neoseiulus cucumeris, are the realistic flowering option and they work.
7. Keep treating for two weeks after it looks fixed. New growth coming in clean is the only indicator you have, and it lags the actual population.

When to give up on a plant#

Worth saying plainly, because it is sometimes the right call.

A heavily infested plant in mid flower, in a room with other plants you want to save, is a reservoir. Removing it may cost you one harvest and save the rest. Growers who try to nurse the worst plant through routinely lose the whole room.

Afterward#

Clean the space properly before anything else goes in it: wipe the tent interior including seams, replace or wash pots, change the medium.

And quarantine everything that comes in from outside for two weeks in a separate room, with a preventive spray on arrival. That is the only reliable protection against this, and it is the thing nobody does until the first time they meet broad mites.