I am finding it impossible to grow Rocket and Mizuna. Something begins munching away at it soon after it emerges to the point where its not worth planting out. Tiny holes. I cant see any slugs. What could it be? Is there a remedy?
Mark its flea beetles, the classic spring and early summer pest of young brassica leaves. Especially nowadays with oilseed rape everywhere.
Hence my oft repeated advice to wait until early August before sowing these brassica salads, for healthier leaves and also longer harvests through autumn. See the timeline http://www.charlesdowding.co.uk/wp-content/uploads/2014/12/Sowing-timeline.pdf and there is a link to it on second para home page.