If the leaves of your tomato plants appear as though they have been used as target practice at a rifle range, then chances are you have flea beetles. They are a common pest of tomato seedlings. Other plants that can be damaged include: peppers, melons, potatoes, corn, spinach, eggplants, radishes and members of the brassica family (like cabbage, cauliflower, broccoli and brussel sprouts).
Flea beetles can be hard to spot as they are quite small, between 1/16 and 1/8 of an inch and quickly jump when disturbed. They come in a variety of colours from black, bluish bronze, metallic grey, or brown.
Tiny holes peppered over the leaf. This characteristic damage is called ‘shot-holing’. Young seedlings are most vulnerable and can receive enough damage to kill the plant. Mature plants can usually sustain significant leaf damage. Other damage can include blemishes or pimples to root crops like radish, daikon or turnips. Flea beetles are common vectors for bacterial and viral diseases and plants attacked by these pathogens will need to be destroyed.
Flea Beetles over winter as adults, in leaf litter and garden debris. They re-emurge in mid to late spring (roughly mid-May in Ontario) and soon begin mating. The females lay their eggs either singly or in clusters in the soil around the base of host plants through-out the spring and early summer. The larvae then feed on the root hairs and roots of the plants for about 1 month then pupate in the soil. The adults emerge from the soil (about the end of July) feed and then seek hibernation sites in the fall.
There are several natural controls that help reduce flea beetle populations. If your populations are high enough you may want to use a pesticide. Check first when in doubt what is permitted in your local.
Integrated Pest Management
- Beneficial’s: The braconid wasp (Microcotonus vittage Muesebeck) is a predator of flea beetles. They are attracted to anise, cilantro, dill and fennel.
- Flea beetles lay their eggs in the soil and prefer bare soil. Using mulch can help to make it difficult for them to lay their eggs.
- Delay your spring planting by a couple of weeks and plant larger healthy plants. This is especially advisable if you have had a very mild winter or a large flea beetle population the year before. Note: A later plant is ideal for tomato plants anyway as they love the heat and hate the cold. If your tomato seedlings are planted out to early the cool temperatures can set back their development by as much as 2 weeks.
- Crop rotation is recommended when possible.
- Clean up garden debris and fallen leaves in the fall to minimize overwintering.
- Turning over the soil in the fall will help to expose the fleas to birds and may destroy their winter hangout.
- Diatomaceous Earth (Silicon Dioxide) is said to work for fleas (although I have not tried it myself for this purpose). Diatomaceous Earth is the ground up fossilized remains of one celled diatoms. Their razor sharp edges are capable of piercing the outer surfaces of the insects causing them to dehydrate. It usually used for soft-bodied insects. Diatomaceous Earth comes in a powder form and is sprinkled on dry.
- Covering your plants with row covers or cheese cloth will help to keep beetles away (ensure the holes are small enough to prevent them from getting through).
- Insect repellents that contain garlic, mint, or hot peppers are said to be help ward off flea beetles, these will need frequent reapplication.
Photo credits: all photos have been taken by the author.
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For photos: Kimberley Pacholko Flea Beetle Damage to Tomato Plants – Horticulture For Home Gardeners
For content: Kimberley Pacholko 2021, Ornamental Garden Specialist, Flea Beetle Damage to Tomato Plants – Horticulture For Home Gardeners