Thrips
Thrips are narrow, fast insects about 2 mm long that rasp at leaves and flowers. Damage looks silvery or bleached, with black dots of excrement. Onion thrips streak allium leaves; western flower thrips mark petals under glass.
Pests
What it looks like
Look for a silver sheen rather than holes.
-
Silvery streaks Allium leaves develop pale silver streaks. -
Black specks Tiny black dots of excrement across the damage. -
Marked petals Flowers show pale flecks and distorted petals. -
Slender insects Narrow yellow or dark insects in leaf folds.
How to confirm it
Shake and look closely.
-
Tap onto white paper
Tiny slender insects fall and run.
-
Inspect leaf folds
Thrips hide where leaves meet the stem.
-
Blue sticky traps
Thrips are drawn to blue traps.
What to do
Keep plants moist and humid.
-
Water and damp down
Keep plants watered; thrips favour dry stress.
-
Hang blue sticky traps
Monitor and catch adults under glass.
-
Use predatory mites
Amblyseius mites control thrips in greenhouses.
-
Wash off
Hose leaves and remove badly damaged ones.
Prevent it next time
- Water alliums well in hot, dry spells.
- Clear weeds and debris where thrips overwinter.
- Check new houseplants.
What not to do
Do not spray flowers that bees are visiting; use traps and predators instead.
In the growing guides
Where the guides mention it, with plant-specific advice.
Sources
- Thrips, Royal Horticultural Society