Firstly, he says that some dahlias are more likely to attract earwigs than others. The big decorative dahlias with their layers of petals offer good hiding places for earwigs. So they are more likely to suffer.
But the simpler single and collerette dahlias don’t offer so much cover. So if you really don’t want earwigs, don’t grow the big decorative dahlias.
However, that seems a bit sad. Steve suggests that if you do want to grow them, smear some Vaseline around the main stems. The earwigs won’t be able to get past it.
Steve also says that earwigs may be a pest on dahlias, but they are otherwise an asset in the garden. They feed heavily on aphids, blackfly and greenfly.