Pest
Flea beetle
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Watch for | Watch for in April | Watch for in May | Watch for in June | Watch for in July | Watch for in August | Watch for in September |
What it is
Flea beetles are tiny beetles, about 2 to 3 mm long, that jump like fleas when disturbed. Several species attack the cabbage family. Most are shiny black or metallic blue-green, and some have a yellow stripe down each wing case.
Symptoms
Leaves are covered in small, round holes or shallow pits, often so many that seedlings look as if they have been hit by shot. The beetles are easy to see on a sunny day: tap a leaf and dozens spring away. Badly hit seedlings stall and may die, especially in hot, dry weather. Slugs and caterpillars make larger, irregular holes, and slugs leave slime trails.
Cause
Adult beetles spend the winter in leaf litter, hedges and plant debris, and become active as the soil warms in April and May. They feed hardest in warm, dry, sunny weather. A new generation appears in late summer. The larvae live in the soil and nibble roots, but rarely do noticeable harm in gardens.
Control
Most damage is cosmetic once plants have several true leaves, so the aim is to get seedlings past the vulnerable stage. Water seed drills and young plants regularly, as the beetles dislike damp conditions, and a light liquid feed helps plants grow away. An old trick that works is to pass a board smeared with grease just above the leaves; disturbed beetles jump and stick to it. Sprays are not needed.
Prevention
Cover seedbeds with fleece or fine insect mesh immediately after sowing. Raise brassicas in modules and plant them out once they are sturdier. Sow radish and rocket in early spring or late summer rather than in the hottest weeks, and clear plant debris in autumn where the adults would shelter.
Plants often affected
Could it be something else?
These problems share some of the same symptoms. Compare them, or run the symptom checker with these signs ticked.
Months to keep an eye out: April, May, June, July, August and September.
Sources
Identification and life-cycle details were checked against the references below. Text and advice are our own. See our editorial policy.