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I have had a Senetti (more info) for about 18 months, and last year it was attacked by aphids. Initially the leaves had a worm like discolouration, as if something was attacking or eating them. Are the two things linked?

Some soapy water and some insect spray seemed to eliminate the aphids. I cut off many of the 'infected' leaves which almost killed the plant. I bought some new Senetti recently and they seem to have suddenly exhibited the same worm like attack. I want to save the plants from the same worm like attack

worm like attack

What is it, and how do I get rid of them?

A couple of other things in case they're relevant

  • Balcony is south facing and so I tend to give them a load of water every few days, depending upon weather
  • I do put plant food into the soil to help them grow
  • I seem to have a lot of very delicate spider's webs across some of my other plants (although I've not seen any spiders)
  • I'm on the 7th floor so a fair way up for small flies to come
  • the bees keep coming all the way up, so the plants must be doing ok
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That is leafminer damage. You can control leafminers by cutting off affected leaves, to improve appearance, and remove existing leafminers before they mature (for minor infestations) Spraying with neem oil for the adult insects early in the season before they lay their eggs (this is what I usually do), or using a stronger insecticide to knock out existing larvae. Leafminer damage is not usually very hard on the plant, but it is unsightly. From the picture, it seems that most of the leaves were hit, so I would not recommend cutting them all off. :) That would be worse than the infestation itself. The fastest way is a strong insecticide, but wait until the plant is through flowering, for the bees.

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I'm a grower in a nursery and we have the same problem. This is a leafminer. It would be interesting if you can check if the pupae are still in the leaves or if they fell into the ground, because even if you take off affected leaves the problem can persist as the adults emerge from the ground. These pupae are normally about 5cm deep. Cut and destroy the affected leaves, and try to control if there are pupae under the ground. There are natural predators for this insect, but maybe as you are up there, it is difficult for them to fly.

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