There’s nothing more disheartening than starting your first spring vegetables – salad greens and all kinds of seedlings – and seeing them thrive, only to find them riddled with hundreds of tiny holes, seemingly overnight. Flea beetles are one of the most aggressive and persistent pests that we have to deal with in our home gardens.
You may be one of the lucky ones and not have this problem in your area, but I know from firsthand experience that the UK and much of Europe has been hit with the “flea beetle plague” in recent years. So how do we get rid of them? Can we even kill them at all? Or, most importantly, how do we keep flea beetles away from our beloved plants?
While flea beetles can be very difficult to get rid of, there are sprays that can deter them and barriers to keep them off your plants. The most effective methods are timing your crops during times when flea beetles aren’t active and protecting brassica seedlings with mesh covers from day one.
In this article, we’ll dig into different types of prevention – from timing and sowing strategies – to various types of flea beetle control – row covers, sprays and natural pesticides. So if you’re interested in better protecting your garden this season, read on.
What are flea beetles?
Flea beetles are small jumping leaf beetles that are part of the Chrysomelidae family. They’re as small as a poppy seed and mostly black, although you can find them in brown and similar colours. They’re rarely visible on plants unless you’re intentional and know where to look.
The first thing you’ll probably notice when dealing with flea beetles is the damage they can quickly plague your crops with – tiny holes everywhere. When touching the plant, you’ll notice these beetles jumping off all at once, like fleas jumping off a stray cat – hence the “flea” nickname.
Life cycle – when are flea beetles most active?
Now, since you’re probably not a biologist interested in learning more about insects, here’s the only fact about flea beetles that matters, in my opinion: When are they most active in the season?
This matters, because rather than fighting with nature (a fight that you can’t win, by the way), it’s best that you work with it, and be more prepared during those months when flea beetles are most rampant.
Flea beetle eggs overwinter in the soil and come back to life when temperatures start exceeding 50°F(10°C). By the month of May, you’ll have an army of adult flea beetles that lay eggs and multiply. The eggs then hatch in 7-14 days, and the entire process repeats itself for 1 to 3 generations.
So it’s safe to say that the months of May and early June are the most susceptible to flea beetle attacks.
Unfortunately, these are also the months when many of our seedlings go in the ground, and they’re sitting targets for our flea beetle menace. Don’t worry, there are ways to protect them, but first, let’s see what flea beetles like to have on their menu.
What do flea beetles like to eat – and why should you care?
There are certain plants flea beetles like to eat more than others. And you should care because they’ll either stunt your crops or decimate them completely. Here’s what to keep an eye out for:
- Radishes. Flea beetles and radishes almost go hand in hand. They won’t destroy radish crops though, but sometimes they will get so hungry that they’ll even start to munch on the outter radish skin.
- Asian greens. Arugula, in particular, is another crop that doesn’t stand a chance in May. Other related crops are mustards, mizuna and pak choi. Forget about growing these in flea beetle season.
- Brassicas. All brassicas fall prey to the dreaded flea beetle if left unchecked. Older plants recover just fine, but there are certain seedlings – like rutabaga (swede) – that can become permanently stunted by flea beetle damage. Keep a close eye on your cabbage, kohlrabi and brussle sprouts seedlings.
- Nighshades. Tomatoes, eggplants, peppers and potatoes are also on the flea beetles’ blacklist, altough I haven’t personally had that much damage. I do sow them late and transplant them as large, established plants.
Flea beetles can also attack corn, sunflowers, squash, different types of flowers, and even shrubs – but to a lesser degree, at least not one that makes a difference in the plant’s development.
Three main methods to keep flea beetles off your plants
1. Time your sowings
All gardeners are eager to start sowing in spring, but with certain crops, fighting against flea beetles is too much of a battle. For this reason, certain vegetables are simply best sown in summer, when the danger of flea beetles has passed:
- Sow arugula, mustards, mizuna, and pak choi in early august. They thrive as a fall crop.
- Grow winter cabbages and plant them out in June or July. You’ll still have to deal with the dreaded cabbage white butterfly, but nothing a little BT spray can’t fix.
- Transplant larger tomato, eggplant or pepper seedlings that can easily withstand pest atttacks.
2. Start seedlings indoors or undercover
Starting certain types of seedlings – like most brassicas – outdoors, is neither practical nor recommended. So many things can go wrong – frosts, slugs, and eventually flea beetles will get to them.
That’s why the best way to start these seedlings, in my opinion, is under grow lights, indoors, or in a greenhouse, safe from harmful insects.
Make sure to pot them on at least once and grow them to a decent size. Brassica seedlings should be at least 1 month old, have at least 3 sets of true leaves and be well hardened off before transplanting outside.
3. Use floating row covers for targeted crops
Even if you’ve followed methods 1 and 2, you’ll still need the extra measure of a physical barrier when planting your seedlings out.
This barrier could be either a fleece cover or a mesh floating row cover. I use both, for different purposes. Here’s what I mean:
I use a fleece row cover early in spring to protect my radishes and arugula from frosty nights. The fleece cover, while not perfectly pinned down to the ground, also reduces the chance of insect or bird damage. When flea beetles start to come out, it slows them down, but not significantly. At this point, radishes are strong enough to withstand attacks, while arugula is cropping for the 2nd or 3rd time, and I don’t mind the ruined aesthetics.
You shouldn’t, however, use a fleece cover as a reliable barrier against flea beetles, because it rips so easily. Not to mention that May is way too hot to keep fleece cover on your plants.
The second barrier I use is mesh floating cover. This can be a garden mesh – a tight, UV-resistant insect netting – but it only comes in certain sizes and can get quite expensive. If you’re thrifty, you can purchase tulle fabric and use it as mesh on top of hoops. Whatever mesh you buy, make sure it’s dense enough so that it prevents the tiny beetles from getting through.
I use garden mesh (or tulle) to protect brassica seedlings just as soon as I plant them out. Before planting them out, I make sure the soil is weeded and do my best not to remove the cover (or do so very quickly) until the plants are mature.
An added bonus when using this mesh is that it not only stops flea beetles, it also prevents cabbage butterflies from laying eggs and pigeons from destroying your brassica crop, so it’s basically useful all season long.
In case you trap a family of flea beetles under your cover, you can spray or sprinkle some of the options I’ll describe below, but continuing to use a mesh cover is still your best bet.
Semi-effective ways of deterring flea beetles
Below is a list of measures I’ve tried with varying degrees of success. Some organic pest control methods – like spraying – are labour intensive, and all efforts will be lost at the first chance of rain, which in spring is quite often.
- Spraying with soapy water and peppermint oil. It sounds good in theory (and it smells amazing), but I didn’t find this effective, and studies agree it doesn’t work. Spraying this mixture on greens may get you some results, but the effort of thoroughly washing the peppermint off isn’t worth it.
- Hot pepper spray. I’ve tried this once – beware of the wind direction when using it. Add garlic to it, and you’ve got a spicy bomb that truly does deterr flea beetles…for a little while. Until the first rain comes.
- Diatomaceous earth. Another popular option is sprinkling food grade DE on top of the affected plants’ foliage, and around their base. And while coffee grounds seem to have no effect on flea beetles whatsoever, diatomaceous earth does repel flea beetles to some degree. I would use it in conjunction with mesh row covers, if you see damage underneath.
- Planting a decoy crop. You’ve probably learned by now, as a gardener, that you need to make some offerings to the flea beetle gods if you want them to leave your other crops alone. Have a patch of radishes or arugula left uncovered and hope that the flea beetles will stop there and forget about the rest of your garden.
When it comes to flea beetles, established plants can recover, and other than a few unsightly leaves, there’s nothing to worry about. Potato plants quickly outgrow flea beetle damage, as do squash and corn. It’s the small brassica seedlings you need to worry about, as well as Asian greens (luckily, lettuce isn’t subjected to flea beetle damage).
Hopefully, you’ve learned the importance of perfect timing, planning your garden and making use of mesh garden covers. You can choose to fight annoying flea beetles or simply keep them out and away from your plants using covers. In my opinion, prevention is far more valuable than time-consuming and even harmful “natural pesticides.”