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About a week ago I noticed that some of our Boxwood plants (Buxus Sempervirens) contain a green caterpillar and a few days later the caterpillars had spread rapidly to almost all other Boxwood plants.

After I bit of Googling I found out it's the Box Tree caterpillar, an invasive species that was accidentally spread from Asia to Europe (and my country The Netherlands) 5-10 years ago. Some say that spraying with certain pesticides may help (which I'm reluctant to do because I try to do organic gardening as much as possible), but others say that once the caterpillars are spreading nothing really helps anymore.

Affected Boxwood

I tried to remove all caterpillars I could find by hand (at least 150), but the next day I found about 20 caterpillars which I probably missed. I'm not sure if this approach is effective and I suspect it will only delay the inevitable. I also noticed that almost all Boxwood shrubs in at least a 1 km radius around our block are affected.

So my question is: is there anything (handpicking or pesticide) that really helps against the Box tree caterpillar when they have already spread around the neighborhood?

THelper
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5 Answers5

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Well, there are some things you can do that are "Organic," and safe for the environment. #1 you are already doing.

Handpick caterpillars from plants as you find them. You may need to patrol your garden at night to find slugs and some caterpillars. Relocate the caterpillars to a different area, or kill them by dropping them into a bucket of soapy water. Or feed them to your birds.

Spray the foliage of plants with neem oil. Neem oil controls caterpillars and other pests, including whiteflies, leafminers, and thrips. It may also kill beneficial insects such as bees and earthworms, however just don't spray you plant when they ar are blooming, and you can avoid much of this. To make a longer-lasting mixture purchase Neem Oil and Agricultural Oil to mix with water. You can also, spray with peppermint, lavender, or other essential oils, but for your problem, this would get expensive.

Dust plant foliage with Bacillus thuringiensis, or Bt, powder. Bt is a natural bacteria that kills caterpillars, but it does not harm most other beneficial insects. One of my favorites.

Invite birds and predatory insects into your garden. Hang a bird feeder to attract birds to the area. Ducks and chickens also enjoy eating caterpillars. If your garden lacks predatory insects, such as praying mantises, you can usually purchase a box of them from a garden center. My favorite since I started feeding the birds is a troupe of sparrows that have taken up residence in my Boxwood Hedge, and there is no insect damage anymore. Also, introduce habitat for toads and frogs on your property, in the long run, you pest population will dwindle.

Plant herbs and flowers around your garden to repel caterpillars. Many insects dislike the scent of lavender, mugwort, sage and peppermint. I like to plant garlic cloves among my plants, which drives away pests.

Finally, predators and co-planting are the long term solutions. For now, I would spray and use the bacilli solution. Wasps are a great solution for caterpillars; one big wasp nest will eat a couple of pounds of caterpillars a week if you can stand them. Several plants weirdly attract wasps; my favorite is Sea Holly (Eryngium maritimum). Plant it around your border and see what happens. Remember to put up with some damage, but if this is an invasive species best to eradicate it.

CloneZero
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BT seems the way to go…but whilst I wait for delivery, I’m crushing the little buggers…not so much looking for the caterpillars as homing in on the webby foliage & letting my fingers find them. I’m also trying nettle tea (nettles in water left for a few days). Someone suggested it for cabbage white caterpillars & I was blown away with how effective it was. Caterpillars totally despatched and of course it’s also a feed. Time will tell if any of this helps though!!

Canalstar
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Spray the box plants with Zen Tari (available on line) Buy pheramone traps from dragonfli.co.uk

The lures in the trap attract the moth and this breaks the cycle. Zen Tari, sprayed onto the leaf means that the caterpillar dies within a day of eating the sprayed leaf. You have to be vigilant and check box plants regularly and spray again if necessary. Do this March-October I am afraid. Or swap your box for something they don't like!

user26098
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I have the most organic suggestion - do nothing. This will last just one year. Your boxwood will lose all leaves but will also recover the next season. More than half of your neigbors will take their boxes out, thinking they are dead. But they won' t be.

This is just one-year phenomenon, without long term effects at all!

Aleksandar M
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Last year my beautiful box was attacked. Only on one end I saved the rest, I brewed up garlic rosemary and crushed tomato plant leaves let it steep in boiling water for 24hours and sprayed the living daylights out of my box. I watched as the moths took flight you can see them leaving in droves seemed to do the trick and I’m doing it again now as the blighters are back

Victoria
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