Flea Beetles: How to Protect Your Brassicas and Radishes

You know the drill, you’ve lovingly sown your radish and brassica seedlings, they sprout with promise, and then bam! Overnight, they’re riddled with tiny holes like someone’s taken a mini hole punch to them. That’s the calling card of the flea beetle: tiny, fast, and ferociously hungry. But don’t panic, there are ways to fight back. Here’s how we keep flea beetles at bay and our crops thriving.

Know Your Pest: What Are Flea Beetles?

Flea beetles are tiny, jumping beetles, usually black, bronze, or metallic blue. They love brassicas (like kale, broccoli, and cabbage) and radishes, especially when plants are young and tender. They chew small, round holes in leaves, and in large numbers, they can decimate a bed of seedlings. The good news? With the right timing and tactics, we can stop them in their tracks.

Cover with Fine Mesh or Fleece

Prevention is always easier than cure. We cover vulnerable crops with fine insect mesh or horticultural fleece from the moment seeds go in the ground. Flea beetles are small but not persistent, they won’t dig or push, so a physical barrier works wonders. Just be sure the cover is sealed at the edges with soil or bricks, no gaps!

Keep Soil Moist and Plants Growing Fast

Flea beetles love dry soil and stressed seedlings. We water regularly, especially in hot weather, and mulch around plants to retain moisture. Strong, fast-growing plants are more resilient and can often outgrow the damage. A bit of compost or liquid seaweed feed gives them the extra boost they need.

Sow Thickly and Successionally

We never sow all our brassicas and radishes at once. Flea beetle pressure is highest in spring and again in late summer, so we stagger sowings to avoid peak infestations. We also sow a bit thicker than usual, yes, we’ll thin later, but it gives us a better chance of getting a good crop even if some plants take a hit.

Use Trap Crops

Certain crops are flea beetle magnets. We often sow a row of mustard or pak choi as a decoy, they attract the beetles away from our main crop. Once the trap crop is infested, we remove and compost it (far away from the garden), breaking the beetle’s feeding cycle.

Disturb the Soil Regularly

Flea beetles lay their eggs in soil at the base of host plants. By hoeing lightly around the base of your crops or disturbing the surface with a hand fork every few days, you can dislodge larvae and reduce future populations. It’s a small step that adds up.

Keep It Clean Between Crops

After harvesting, we clear away all plant debris promptly and compost it properly. Flea beetles can overwinter in crop residue, so a tidy rotation helps reduce the next season’s population. We also rotate beds each year to avoid building up a flea beetle hotspot.

Flea beetles might be tiny, but they can do serious damage if left unchecked. Thankfully, with a combination of barriers, good soil care, smart sowing, and natural tricks, we can keep them from turning our brassicas and radishes into holey messes.