Tiny but not insignificant: Flea beetle

Nothing in gardening is simple. There is always a catch to almost anything you try. The nicest plants always seem unattainable or expensive, that plant you have always wanted will be sold out an hour before you get to the nursery and the most fragrant rose will also be the gangliest and most prone to disease. Well that’s how it sometimes seems.

Nowehere is this more evident than in the veg garden. We know that cauliflowers are difficult to grow, that celery is almost impossible and that asparagus takes years. So hooray for turnips and radishes. They are easy and quick to grow. Nothing could be simpler.

Well, not quite.

Both are brassicas, meaning they are related to cabbages, mustards and pak choi. We know these are good for us. They are packed with sulphur-containing mustard oils and these have masses of health benefits.

That hot taste does us good. I can only assume that the plants developed these chemicals to prevent attack by grazers. This is not unknown  among plants: many produce chemicals that inhibit insect attacks. The most famous are salvestrols which are chemicals produced by plants when they are attacked by pest or disease. They have a bitter taste and help protect the plant. Incidentally, these have anti-cancer properties and it would not be unreasonable to extrapolate that it is better for you to eat cabbages that have caterpillar damage than perfect veg that is pumped full of fertiliser – veg that has had to struggle may be more bitter than force-fed sweet veg but that very bitterness does us good.

That is an interesting theory – what we actually know is that eating more veg is good for us so eat more veg, however it is grown.

While these mustard oils may put off some pests (though I can’t think of many pests that will not attack a cabbage), they also attract others. Cabbage white butterflies home in on brassicas to lay their eggs and another pest that is very fussy about what it eats are flea beetles.

There are dozens of flea beetle species and though most like brassicas, some have a more catholic diet. But it is the brassica-eating species that most affect gardeners. Those I found in the garden yesterday are Phyllotreta undulata (I think) the turnip flea beetle or small striped flea beetle. It is a tiny thing, just 2mm long, black with two yellow ‘go-faster’ stripes down the side. And true to their name, they were on turnips.

These tiny creatures get their name from the way they use their (comparatively) large hind legs to jump great distances when disturbed. They feed by chewing small holes in the upper surface of the leaf. This results in small holes and sometimes dead patches. The trouble is that they seem to appear from nowhere and attack the seedlings as soon as they appear. If they waited till the plants were bigger there would be plenty of leaves for all of us. But they don’t and they can decimate rows of radish, turnip, swede, rocket, mizuna seedlings and so much more.

The damage is not really critical for rootcrops if it is minimal but it is a problem on salad leaves which look far from appetising when full of holes.

The beetles overwinter in leaf litter and rubbish and come out to feed in spring. They mate and the grubs feed on brassica roots and hatch as adults again in late summer. It must be really tough in winter if you are a tiny beetle 2mm long! If you live in a rural area you will probably get zillions of the beetles off nearby rape fields.

Control is difficult. Because the beetles jump up when disturbed you can run a yellow greenhouse ‘sticky trap’ over the young plants to catch them. How you let them die after that is up to you! There are pesticides that may give some control. What is important is that you water and feed the crop so it gets a chance to grow out of the damage. This is helpful for radishes and turnips anyway which are best when grown fast – drought-stressed radishes are not pleasant.


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8 Comments on “Tiny but not insignificant: Flea beetle”

  1. derrickjknight
    July 17, 2019 at 9:18 am #

    Interesting facts about turnips, radishes, and beetles

  2. Kathy Larson
    July 17, 2019 at 12:42 pm #

    In our Iowa garden,flea beetles mostly attack the eggplant.If we don’t dust with Sevin as soon as the first drill holes appear,they rapidly kill the plant.Only a couple of treatments needed,then they’re gone (till next year).

    • thebikinggardener
      July 17, 2019 at 1:12 pm #

      That is interesting. They must be a different species and in Northern Europe we don’t have that problem. ‘Just as well since we don’t have Sevin (carbaryl) either. The range of insecticides available to amateurs is very limited compared to the USA.

  3. Anne Cullen
    July 17, 2019 at 5:12 pm #

    I had this beetle on Rhubarb leaves earlier in the year

    • thebikinggardener
      July 18, 2019 at 7:36 am #

      Despite the fact that rhubarb leaves are commonly regarded as ‘poisonous’ many pests will attack them, including some flea beetles though I am not sure they are the same species as the ones that attack brassicas. Green dock beetles (which are bright green) attack rhubarb, which is closely related to dock and there is also a new pest beetle in the UK which may be present in Ireland.

  4. Meriel
    July 18, 2019 at 12:25 am #

    Oh how true regarding ‘gardening not being simple’. How often have I thought ALL of those things! Some years ago I had, what I now know (from you) were some type of flea beetle on veg and many other plants in the vicinity. They practically stripped all the leaves & were quite difficult to catch. I did eventually & posted to Teagasc but never got a response. Nobody I asked seemed to know them. They persisted for another year or more but thankfully disappeared – are at least kept to reasonable numbers! I will at least know now if there is a next time. Thanks.

  5. tonytomeo
    July 22, 2019 at 5:49 am #

    These supposedly have potential to be a serious problem where cruciferous vegetables are grown in the Salinas Valley, but I have not heard anything about them in a long time. They do well in the naturalized wild turnip and mustard here, but do not ruin all of it. No one mines a few nibbles in their greens.

  6. Marie OLeary
    July 26, 2019 at 12:49 pm #

    Thank you for that very interesting information it is much appreciated.

    Regular follower Marie.

    On Wed, Jul 17, 2019 at 7:11 AM The Biking Gardener wrote:

    > thebikinggardener posted: “Nothing in gardening is simple. There is always > a catch to almost anything you try. The nicest plants always seem > unattainable or expensive, that plant you have always wanted will be sold > out an hour before you get to the nursery and the most fragrant ros” >

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