Overview
London rocket flea beetles are small jumping beetles that feed on leaves, particularly in young plants. Their feeding creates small holes in foliage, which can be especially damaging to seedlings. In severe cases, entire plantings may fail due to repeated feeding.
Flea beetles are known for their ability to jump when disturbed, making them difficult to control. Their damage is often most severe during early plant growth stages.
They are part of a larger group of chewing pests covered in the Garden Pests section.
The Spring Jumper: London Rocket Flea Beetles
The London Rocket Flea Beetle (primarily species in the genus Phyllotreta) is a small, energetic pest that becomes highly active in the early spring throughout the American Southwest, including the Tucson area. These beetles are named for their primary wild host, London Rocket (Sisymbrium irio), a common winter weed. However, once the desert heat dries up their weed hosts, these beetles quickly migrate to vegetable gardens in search of fresh greens.
Identification and “Flea-Like” Behavior
These beetles are tiny—usually less than 3mm long—and are typically a metallic black or dark bronze. They earn the name “flea beetle” because of their enlarged hind legs, which allow them to leap great distances when disturbed. If you reach toward a leaf and the “black dots” suddenly vanish, you are likely dealing with flea beetles.
The “Shothole” Damage Pattern
The damage caused by London Rocket Flea Beetles is highly characteristic and easy to diagnose. Unlike caterpillars that eat from the leaf edges, flea beetles chew small, circular holes right through the middle of the leaf. This results in:
- Shothole Appearance: Leaves look as though they have been peppered with miniature buckshot.
- Seedling Vulnerability: While mature plants can tolerate some “lacing,” young seedlings can be stunted or killed overnight if the beetles consume too much photosynthetic surface area.
- Target Crops: Beyond London Rocket, they favor Arugula, Radishes, Kale, and Bok Choy.
Management in Gardens
The best way to manage these pests is to manage their habitat. Since they overwinter in London Rocket weeds, removing winter weeds before they go to seed can significantly reduce the local beetle population. In the garden, Floating Row Covers are the most effective physical barrier for young crops. For an organic spray option, Neem oil or Pyrethrin can be used during peak activity, though they must be applied directly to the beetles to be effective.
Damage
- Small holes in leaves
- Seedling death
- Reduced plant vigor
- Stunted growth
Management
- Protect seedlings with covers
- Monitor early growth stages
- Encourage beneficial insects
- Use targeted treatments if needed