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How to remove brown ants in old wisteria?

We have moved to a different home and I have an old wisteria vine on my verandah, which I have been pruning back because it was a bit wild. I have discovered ants have been making nests in the old trunk, and making a "slurry" of the timber. I've been digging the "slurry" out a bit and taking off the old layer of bark, which is how I discovered the ants. They are big ants, light brown in colour and not aggressive. I did a bit of google searching and they appear to be coast brown ants.

My question is, how do I get rid of them without damaging the plant? This old trunk is about 10cm thick and there are other trunks only about 2 -4cm in diameter, which appear uninfested. The old trunk still has some shoots coming off it and I also don't want the ants to hop across from the old trunk to the healthy ones.

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Comments

EricL

Hello @Gemma2

Welcome to the Bunnings Workshop community. It's sensational to have you join us and thanks for sharing your question about your old wisteria.

To get rid of the ants without harming your wisteria, you’ll want a targeted approach. Since the ants are inside the old trunk, a borax-based ant bait would be a good option. You can find liquid ant baits at the store, which the ants take back to the nest, gradually eliminating the colony. Placing the bait near the base of the wisteria should encourage them to take it without directly applying anything to the plant.

If you want a more natural method, you could try diatomaceous earth (DE), which dehydrates insects on contact. Sprinkling food-grade DE around the base of the plant and into the cavities where the ants are nesting might help reduce their numbers without affecting the plant. Just reapply after rain.

Since you've already been digging out the "slurry," you might also consider using a garden hose with strong pressure to flush out the nest, then letting the area dry out fully. Ants like dry, undisturbed wood, so keeping the area damp for a few days might encourage them to leave. You could also apply horticultural oil or neem oil lightly to the exposed wood, as ants dislike it.

If the old trunk is badly damaged, it might be worth considering whether removing it entirely would be the best long-term solution. But if it's still supporting new shoots, then baiting and making the environment less attractive should help keep the ants from spreading to the healthier trunks.

If you need further assistance, please let us know.

Eric

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