Every vegetable garden has to deal with pests. Some types of pests can cause problems for a
wide range of different crops, and others are more specific, affecting only certain types of
plants, and causing more damage during at specific times during the growing season.
Like so many growers, I've had to deal with brassica flea beetles in my vegetable gardens,
and their impact can be quite problematic, especially in the spring with the young
seedlings of this diverse range of cabbage family vegetables, I have tried a number of different
methods of preventing these tiny beetles from chewing tiny holes in all of the young leaves,
but have not had great success. More recently I have been trying a much more direct method at
reducing the population of flea beetles in the gardens, and it seems to be fairly successful.
I like to sow a wide range of the brassica family crops into the gardens in the spring,
especially the fast growing radishes, turnip, rocket, arugula, Pak Choi or other greens which
can be the first crops available to harvest in the new season. But all of these plants
seem to also be the preferred food for the flea beetles, especially when they come out
of hibernation in the spring. And I also like to get crops like broccoli or Calabresi, cauliflower,
kale and kohlrabi in the ground quite early, and they can also be affected by the flea beetle.
But I usually transplant these plants as larger seedlings into the gardens and are apparently
less attractive to the flea beetle, if the other faster growing direct sown crops are nearby. If
there is a bad infestation of these beetles, and the conditions are not great for quick growth of
the plants, so many tiny holes can be chewed in the leaves that the plants can really suffer. Most
of the time the plants are able to eventually grow out of the damage,
but the more holes there are in the leaf or salad crops, the less we want to eat them. There
are of course a number of different options for dealing with this pest, apart from the pesticides
that I want to avoid. These include covering the crop with very fine netting or other barriers,
using sticky traps to capture the beetles when they jump, providing good growing conditions for
the plants so they can quickly grow out of any damage, growing companion plants that deter the
beetles or which could attract or host beneficial predators, or growing a trap or sacrificial
crop of plants that the beetles prefer, so that the other brassica crops are spared.
I have often used barriers to try to prevent the flea beetles from getting into the crop, including
horticultural fleece or a very fine mesh. But I have not found these to be overly successful,
mainly because I think the beetles simply crawl underneath the edge of the material. I
have tried sealing off this access by weighing down the edge with even more stones and pieces
of wood, and I found that it was easier to dump a line of soil over the edge of the netting to
properly seal off any gaps. This did seem to be a more effective barrier but it needed to be re-done
every time I wanted to get to the crop underneath for weeding, thinning or harvesting. And it only
worked at keeping beetles out, and if they were already hiding in the soil of the bed or among the
older plants, weeds or debris, then the mesh was only keeping them in. So I have found barriers
like this to be useful, but not ideal for the small scale and diverse context I'm growing in.
The idea of growing a trap crop or a sacrificial crop to attract the flea beetles away from the
main crop is an interesting one, but I've been hesitant to give up part of the garden for this
kind of approach. But more importantly the radish, rocket, turnip or other crops that
would be ideal to attract this particular pest are also crops that I really want to
grow. But in the past I have reverted to this trap crop approach unintentionally,
by abandoning the crops that were badly impacted, effectively leaving them for the pest. But
then I got the idea of starting to treat them as an actual trap crop and I used my flame weeder
to singe or burn the abandoned crops, hoping to kill many of flea beetles in the process.
I have done this occasionally for the past few years, sometimes torching older crops that are
badly affected, and sometimes scorching seedlings that are already showing signs of damage,
giving up on a crop early and hopefully killing the flea beetles in the process,
so that I could get a replacement crop sown instead. I have also transplanted clumps of
brassica greens like rocket or arugula from the polytunnel into the bed of the outside gardens
before sowing the other crops to intentionally attract any flea beetles that were around. And
then a few days later I used the flame weeder to singe or burn the clump of plants. And
this seems to work, or at least it can reduces their numbers quite a bit.
I have been experimenting with this type of trap and burn approach, and have been more focused and
successful with it this year. Early this spring I sowed several clumps of a mix of radish and rocket
or arugula seeds in most of the beds where I was planning to grow brassica crops. These
are both fast growing plants that are quick to germinate even in the cool conditions of
the spring, and the flea beetles seem to find particularly attractive, and which I also had
lots of seed of. When I saw signs of holes in the leaves of the seedlings, I used my flame
weeder to burn the small patches, killing many of the flea beetles in the process. And
in some cases I sowed a second series of clumps in the same manner,
to attract and kill any other flea beetles that were missed with the first batch.
This basic approach seems to work, and I think is particularly useful early in the spring in
killing the adult flea beetles just as they're becoming more active after the long winter,
and hopefully before they've a chance to reproduce. And I think this is one of the key
beneficial aspects of this approach, with a focus on reducing the numbers of pests at the beginning
of the season which will hopefully lead to a significantly lower population later in the year.
As a basic strategy I think this works, attracting the flea beetles to a particular
spot and then killing them. But of course it isn’t perfect and I still haven’t figured
out the variations of this particular method that works best in my context.
I like the small clusters of seedlings, and it seems that the flea beetles will travel quite far,
so perhaps a few scattered clusters throughout the gardens is enough to attract in any flea beetles
that are around, assuming that there aren't any other plants or crops for them to eat. And
I think it's better to torch the plants when they are quite small rather than waiting until later.
The larger the seedlings get, the longer it takes to burn the patch, and I suspect that some of the
beetles might be able to survive under the more dense foliage or have the time to find shelter
in the soil. And the longer I wait the more of a chance there will be for the flea beetles to have
eaten enough to be able to reproduce. I also want to use less heat to avoid heating up the soil too
much, or increasing the chance of collateral damage with other insects or organisms in the
soil. And using less fossil fuel in general is preferable, but I want to make sure that I use
enough heat to actually kill the flea beetles. So, I think the small patches that are not too densely
sown, and that are singed with the torch when the seedlings are still quite small, or as soon
as there is significant signs of any flea beetle damage, is generally the better approach. And then
to sow another batch of trap crops or to have a continual succession of traps sown over the course
of the spring, and possibly even later in the year whenever there is enough space in the gardens.
This is the general strategy that I am working towards, to regularly use these trap and burn
crops, rather than the more conventional use of a trap crop which is there to simply distract
the pest away from the other crop. And this is a very different strategy than how I used to manage
things. Thinking back to the early years of the gardens, I don’t remember flea beetles being a
significant issue. And I think this is because there were very few of them in the landscape
as there didn’t seem to be very much for them to eat in the former
pasture. But over the years of growing an excellent food source for these tiny beetles,
their population increased to the point where they became a problematic and pervasive pest.
Effectively I was breeding the pests by giving them with lots to eat and a habitat to live in
and not using any barriers or other ways of limiting their numbers.
And I used to simply abandoned the damaged crops, leaving them in the ground for a lot longer that
I probably should have, and not dealing with the increasing problem. And all that just led to more
damage the next season.
So my strategy now is to actively work to reduce the population of flea beetles
in and around the gardens, and then to keep the numbers low, and I seem to be having significant
success with this strategy. The beds of the gardens were I had grown trap and burn crops
seem to have had less damage that the other parts of the gardens where I didn’t get around
to sowing the attractive clusters of seedlings for the flea beetles to eat. The crops of turnip,
rocket and radish that were sown at the same time in different parts of the gardens seem
to have fewer holes in the leaves in locations where there had previously been a trap crop. Of
course this correlation isn’t enough to prove anything, especially after just one season,
and there could be other factors that are contributing to this difference,
but it is enough for me to continue with this strategy. And I know that I'm killing at least
a few of the flea beetles with this method, and I haven’t figured out a better option yet. I am not
really aiming to eliminate the population of flea beetles in the area, which would be difficult in
the diverse landscape that we are creating. But I do want to get to the point where the damage that
they cause is inconsequential, or at least that I am not worried about it. And I can always use the
barriers or fine mesh covers as well, to not rely on just on method of pest control, especially if I
want to produce a crop of salad leaves that don’t have any holes in them at all. And I think these
barriers will be more effective if the population of this pest is lower, and any flea beetles that
around are given an easier food supply nearby. So these trap and burn crops have become part of the
preparation of the garden each spring and a tool to use periodically throughout the growing season.
Sowing a succession of these small patches of trap crops scattered across the gardens in the
spring and early summer, and then burning them a short while later, has become another of the
many tasks that we regularly do on the gardens. At least until I get a better sense of how well
it actually works at significantly reducing the damage caused by this pest in the long term,
or until I find a better or easier option to achieve the same result.