Flea beetles are incredibly destructive in the garden. They can also be very hard to control. Learn my multi-pronged flea beetle control method here. It is broken down step-by-step.
Identify The Flea Beetles
First things first, you need to know what you are looking and if it is actually flea beetles you are dealing with. They are tiny little black beetles approx. 2.5 mm. They are often in large numbers and when disturbed they appear to pop off the plant in a frenzy.
Flea beetles can be all black, black with a stripe, brown or even tan in colour. There are many different flea beetle species: pale striped flea beetle, tuber flea beetle, spinach flea beetle, sumac flea beetle, red-headed flea beetle, corn flea beetle, sweet potato flea beetle, horseradish flea beetle. These will be unique to where you live and your climate.
Identify Flea Beetle Damage Symptoms
It starts out with tiny pin hole type marks all over the leaves. This will eventually grow to the entire leaf being consumed.
Flea Beetles Favourite Plants
Flea beetles LOVE the tender young seedlings in the Brassica family (cabbage, kohl rabi, kale, bok choi, radish, cauliflower, broccoli, brussels sprouts).
Some of their other favourites are nasturtium, some varieties of lettuce, mustard.
It’s important to note that flea beetles do not typically like the older plants once the leaves have grown more tough. Once your plants mature they typically become much less of a problem. However, I have found that the exception to this is plants that always are tender such a bok choi, mustard, alyssum and some lettuce varieties.
When Are Flea Beetles A Concern?
Often their is two generations that will affect your garden.
Typically in the early part of spring. They are are often the first pest to show up as they tolerate cooler temperatures. They are partial to drought conditions which makes them prevalent longer into the season and they may show up earlier in the fall.
The larvae overwinter in the soil and will emerge right at the same time as your seedlings as adults.
Once the temperatures start to cool in the fall they will often reappear. If this is combined with dryer august temperatures than they can be particularly tenacious in the fall.
Organic Flea Beetle Control
Prevention is much easier that trying to kill or control them so we will start there. Also a multi-pronged approach I have found to be most beneficial. Ie. don’t place all your eggs in one basket but rather implement several methods as flea beetles are very tenacious.
1. Row Cover
A row cover fabric places on your new seedlings as soon as they emerge can create a barrier over the plants. Two things to note here. First, if you have had flea beetles in that same spot last season the could emerge under your cover. Second, flea beetles are teeny tiny and can get in to some extent anyways from my experience.
2. Diatomaceous Earth
I use this ALWAYS and OFTEN when the flea beetles present themselves in the spring to get my seedlings through their first weeks to maturity. I use this in conjunction with row cover fabric.
It is very simple, you just dust the plants thoroughly. It can be washed off by irrigation and by rain which will then require reapplying. There is just no way around it. It is worth the effort though.
DE (diatomaceous earth) is made from the fossilized remains of tiny, aquatic organisms called diatoms these cut the bodies of the flea beetles (and any other insect that comes into contact) when it is dry. It also works as great deterrent. The flea beetles stay off where ever the plant is covered.
Please note this is not selective to just flea beetles it will affect anything that comes into contact with it. Always use only when necessary.
This is what I use in my garden:
3. Neem Oil
Neem oil is used a natural insecticide in a lot of organic gardens. It is a oil that is produced from the neem tree in India. You dilute it in water & soap and spray down the plant with it. You can find my full detailed recipe by clicking this link here.
You can purchase neem oil online at this link. You can also usually find it at your local Indian grocery store.
Neem oil is not palatable and one the plant is coated deters the flea beetles. It all also affect their reproductive capabilities to reduce future numbers. Please note this is not selective to just flea beetles it will affect anything that comes into contact with it. Always use only when necessary.
4. Trap Cropping
This basically means use another more tempting plant to attract the flea beetles to instead of the ones you don’t want them to destroy. Some common examples are using nasturtium or alyssum as trap crop plants. You will basically be sacrificing one plant for another so you need to understand that going into.
5. Crop Rotation
Don’t plant the same plant in the same spot year after year, especially if you have had a pest or disease problem in that spot before. The bugs & the disease could just be overwintering in the soil. If you plant the same thing again in the same spot, you have just made a very easy dinner for them.
Move your plants around the garden from year to year. Perhaps even give a rest to a certain crop for a season or two if you don’t have a big garden to rotate your crops in.
6. Cultivating The Soil
The larvae can be killed with cultivating and hoeing the soil. Also be sure to remove old plant debris from the garden that they can use to overwinter under. Keep the garden weed free as much as possible in the spring to limit their food as they love those tender young seedlings.
7. Parasites & Predator Insects
Generalist predators such as larvae of lacewing (Chrysopa spp.), adult big-eyed bugs (Geocoris spp.) and damsel bugs (Nabis spp.)are known to feed on adult flea beetles. Planting a home to attract these beneficial bugs to your garden is a good best practice. They are attracted to chamomile, dill, clover and marigold as they are both nectar and pollen-producing.
8. Insecticidal Dust
Beware, these will say they are naturally derived but still a chemical control and not an organic method to control flea beetles. It is not a once and done either, which means you will need to keep applying it as the flea beetles are very mobile. I would rather yank the plant than apply this in my garden but please do your research and decide for yourself and garden.
Always look for ways to attract the so called “good bugs” to the garden. The predators will keep the unwanted “pests” that eat our precious garden at bay.
9. Keep Transplants Indoors Longer
A great option but certainly not for everyone. If you have an indoor grow set-up and extra space (we all know that is limited in the spring), then you can consider keeping flea beetle prone plants indoors longer. Typically you will need to have them in bigger pots of accommodate more grow time, grow lights to keep them healthy and strong and adequate feeding schedule so they don’t fall behind.
I have done this in seasons past for things like bok choi that get devoured no matter their size. Once I saw the flea beetles eased up on some of the hardier plants like kale then I transplanted them outdoors. This could mean an additional month indoors which can be a lot. Again you to decide. Maybe test it out with a few plants and see how it goes.
Now you do want to ask yourself if it is worth your time and effort to continuously treat the plants. Depending on where you are in your season you may want to harvest everything you can and then pull the plants.
If it is early spring and your seedlings just sprouted or you just transplanted then likely it is worth your effort and time to get them through those first weeks. This you will have to decide for yourself.
You may also have to make the hard decision of just pulling the really damaged plants and moving on with something else in it’s place.
Lastly you can be a total garden nerd like myself and do nothing but watch the predator insects eat the bugs that are eating my garden lol. Here is a little video of me nerding out over the predator insects in my brassica’s.