- Flea beetles are common pests found on many vegetable crops including radishes, broccoli, cabbage, turnips, eggplant, peppers, tomatoes, potatoes, spinach and melons.
- Flea beetles chew irregular holes in the leaves.
- Severe flea beetle damage can result in wilted or stunted plants.
- Flea beetles are best managed through a combination of cultural and chemical control methods.
How to identify flea beetles
Most adult flea beetles are very small (1/16 –1/8 inch long). An exception is the spinach flea beetle, which is 1/4-inch long.
- Flea beetles can be black, bronze, bluish or brown to metallic gray.
- Some species have stripes.
- All flea beetles have large back legs which they use for jumping, especially when disturbed.
The most common flea beetles in Minnesota:
- Crucifer flea beetle (Phyllotreta cruciferae)
- Striped flea beetle (P. striolata)
- Western black flea beetle (P. pusilla)
- Potato flea beetle (Epitrix cucumeris)
- Spinach flea beetle (Disonycha xanthomelas)
Most flea beetles feed on very specific plants, but the pale-striped flea beetle (Systena blanda) feeds on a variety of plants, like squash, beans, corn, sunflowers, lettuce, potatoes and many weeds.
- Flea beetles live through the winter as adults in leaf litter, hedgerows, windbreaks and wooded areas.
- Adult flea beetles become active in early spring. Depending on the species, females lay single or clusters of eggs in small holes, in roots, soil, or leaves of many vegetables as well as occasionally on flowers and ornamental shrubs and trees.
- Small white larvae hatch from eggs and feed on the roots of the newly planted seedlings.
- Larvae then transform into pupae in the ground. There are usually one to two generations per year.
Damage caused by flea beetles
All types of flea beetles cause similar damage.
- Adult flea beetles cause the most damage by feeding on the leaves and stems.
- They create shallow pits and small rounded, irregular holes (usually less than 1/8 inch) in the leaves. This type of damage is unique to flea beetles.
- Plants started from seeds are less tolerant of feeding damage compared to transplants, but both can be severely injured if flea beetle numbers are high.
- The larvae usually cause little to no damage to the plants (with the exception of potato flea beetle larvae).
Managing flea beetles in home gardens
Flea beetles are most damaging in spring. It is important to monitor their activity as soon as seedlings have emerged.
- Place yellow sticky traps in your garden to see if you have flea beetles.
- Check your plants for flea beetles and their damage.
- Prevent severe damage to your plants by treating seedlings when there are more than five flea beetles per plant.
- Protect your crops if 10-30% of leaves on seedlings and transplants have dropped off.
It is generally not necessary to treat flea beetles during summer, especially at the end of the season. By summer, crops reach the 4- or 5-leaf stage and are strong enough to survive feeding damage. The number of adult flea beetles also goes down at that time.
- Control weeds in and around planting sites to limit food sources for flea beetles.
- Remove old crop debris so that beetles will not be able to get protection in the winter.
- Plant crops as late as possible. Plants grow faster in warmer temperatures and are more stable to resist damage from flea beetles.
- Use row covers or other screening to keep beetles out when the seedlings are growing.
- Remove row covers before the flowers come up so pollinating insects can reach the plants.
- Plant a highly-favored crop, such as radish, as a trap crop, before you plant your main crop.
- Adult flea beetles will be attracted to the tallest, earliest crops available.
- Once beetles are actively feeding on the trap crop, spray with a labeled pesticide.
Microctonus vittatae is a native braconid wasp (found more commonly in the eastern half of the U.S). This wasp kills the adult flea beetle. The wasp larvae develop on the female flea beetle and prevent the beetle from reproducing. They are not available for purchase.
There are many insecticides labeled for treating flea beetles. Be sure that the vegetable you wish to treat is listed on the label of the pesticide you intend to use. Also, be sure to observe the number of days between pesticide application and when you can harvest your crop.
Below are names of active ingredients that are commonly available in insecticides sold in stores that sell garden pesticides:
- lambda cyhalothrin
CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Be sure that the plant you wish to treat is listed on the label of the pesticide you intend to use. And observe the number of days between pesticide application and when you can harvest your crop. Remember, the label is the law.
Flea beetle management for farmers
- Shortly after planting, keep an eye out for flea beetle damage (beetles are highly mobile so looking for damage is easier).
- Feeding is similar across both plant and beetle species. Beetles leave numerous, small (less than 1/8 inch) holes across leaves, often referred to as “shothole” damage.
- Yellow sticky cards can also be used to detect flea beetles.
Planting later in the “normal window” may help plants avoid the first generation of flea beetles. For example, in cole crops, planting later can help avoid the overwintering of flea beetle generations. In potatoes, planting later, with warmer temperatures, helps potato plants grow quickly, minimizing the impact of flea beetle feeding.
Remove crop debris after harvest to prevent flea beetle feeding, hopefully reducing the strength of future generations. This is especially important at the end of the season, as cleaning up will help reduce overwintering sites.
Trap crops can be used as sacrificial planting that is intended to be highly attractive to insect pests and thus draw pests away from the main crop.
In cole crops, trap crops have been studied and used with success in other states.
- Trap crops must be planted earlier than the main crop to draw flea beetles into them (typically 7-14 days in advance).
- Trap crops should be planted to 10% of the crop area and can be planted along the field border or along a single side of the field.
- Variety is also important, with studies in Washington finding Pacific Gold Mustard and Pac Choi to be most effective in drawing flea beetles to them.
- There have also been studies suggesting that trap crops made of three brassica species were more effective than those made of one or two species.
As long as crops are being rotated, row covers can exclude flea beetles feeding. The row cover will make weeding difficult, and flea beetles may get under the cover whenever it is lifted. For eggplants, you will need hoops as the row cover cannot lay directly on the eggplant.
There are native parasitoids of flea beetles (Microctonus vittatae Muesebec), though they are not very common. They are not available for purchase.
Generalist natural enemies like lacewing larvae have been observed feeding on flea beetles
Treatment on all cole crops is recommended when 10-20% of a stand shows feeding damage. Seedlings are the most susceptible, though it will also be important for crops where they feed on the harvestable portion of the crop. Treatment may be needed sooner where cole crops are started from seed as heavy infestations will destroy seedlings before they emerge.
Eggplant seedlings are also preferred by flea beetles. When plants are small (less than 3 inches), consider treatments when there are two beetles per plant. As they grow, they can tolerate more damage. When plants are 3-6 inches tall, the threshold is 4 beetles per plant, and when they are more than 6 inches tall, an 8-beetle-per-plant threshold applies. Flea beetles will be slower in cool weather, scouting for them is easier on cool mornings.
Feeding damage and beetle populations can be spotty across a field (or along field edges) so spot-treatments within fields can be effective, reducing insecticide use and costs.
Kaolin clay can provide a physical barrier to feeding, though studies (and grower experience) with this method report mixed results. This will need to be applied after it rains.
To ensure proper use of insecticides, refer to the Midwest Vegetable Production Guide.
Reviewed in 2022