Web forming caterpillars

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KatG

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Web forming caterpillars
« on: August 20, 2016, 01:36:04 PM »
Recently I have noticed several Euphorbia have been damaged by web forming caterpillars. They seem to be particularly attracted to Euphorbia rigida, and have destroyed around 50% of those I planted earlier this summer. They have also inhabited a Euphorbia umbellata 'Ruby' which is in a pot. The advice gleaned on-line is that one should pick off the web, but I have found this to be ineffective. By the time the web becomes noticeable the damage is done, and some eggs always remain and develop into more caterpillars. I have tried washing them off with a jet of water, but I suspect this just creates favourable conditions for the previously invisible caterpillars which have already burrowed into the stem. I suspect the occasional watering of young plants may have encouraged the pest too. Any ideas?
Katerina Georgi. Interior designer and Garden designer. Has lived, worked and gardened in the southern Peloponnese for the last 26 years. MGS member and head of MGS Peloponnese Branch.

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MikeHardman

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Re: Web forming caterpillars
« Reply #1 on: September 10, 2016, 10:17:35 AM »
Tricky!
I suspect a systemic insecticide may be needed, and preferably applied just before the caterpillars hatch from the eggs - so their first bite of the plant is their last. Your experience will be the best guide as to the right time.
Yes, with photos we might be able to ID the moth species. That might be interesting to know, but it won't change the tactics significantly methinks.

Mike
Mike
Geologist by Uni training, IT consultant, Referee for Viola for Botanical Society of the British Isles, commissioned author and photographer on Viola for RHS (Enc. of Perennials, The Garden, The Plantsman).
I garden near Polis, Cyprus, 100m alt., on marl, but have gardened mainly in S.England

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KatG

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Re: Web forming caterpillars
« Reply #2 on: September 30, 2016, 11:22:33 AM »
Thanks Mike. The caterpillars are minute, and enclosed in a hideous mess of web/eggs/dead foliage, and I haven't knowingly seen a moth yet. Very tricky!
Katerina Georgi. Interior designer and Garden designer. Has lived, worked and gardened in the southern Peloponnese for the last 26 years. MGS member and head of MGS Peloponnese Branch.

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MikeHardman

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Re: Web forming caterpillars
« Reply #3 on: September 30, 2016, 09:01:33 PM »
The caterpillars may be minute now, but presumably they are still growing. From previous experience, can you say how big they get?

Of course, the spectacular spurge hawk moth's caterpillar is found on Euphorbia. But they are big and solitary.

I'm curious to know which species of moth you have, but I recognize that it might be difficult to determine.

Mike
Mike
Geologist by Uni training, IT consultant, Referee for Viola for Botanical Society of the British Isles, commissioned author and photographer on Viola for RHS (Enc. of Perennials, The Garden, The Plantsman).
I garden near Polis, Cyprus, 100m alt., on marl, but have gardened mainly in S.England