Flea beetles are here. But need warmer and drier weather to get more active. They make many many tiny holes, about the size small sewing needle. They dont stay at one spot to graze. I have found a solution for this probme: FRENCH NYLON TULLE. Just throw it on any thing. It is wind proof, super light. And air, light and water goes throgh it. AND it is inexpensive. My observation is that FBs like mostly egplants, Chinese lantern, Horse nettle(a weed, eggplant relative. What is more, is that the can only harm small young seedlings.

Wow - bunch of new responses. Where have I been? nygardener - I wonder if the clay has something to do with it. I've heard that Arugula has a lot of calcium in it. Maybe it likes a more minerally soil? When you buy it at the store, there tends to be some sand on it, but I don't generally add sand to my soil (which, last year and this,is mostly mushroom compost). Feijoas - None of my arugula has jumped ship. I let a lot of it go to seed last year - the flowers actually tasted better than the leaves- but I don't seem to have any volunteers anywhere. Natal - Some arugula is spicy but also has a deeper, rich green flavor. Some arugula is just spicy, but not much else. Or at least that's what my tastebuds think.

Assuming from your terminology that you’re in the northern hemisphere, if you sow it soon, then it will grow rapidly over spring and, depending on your climate and soil type, it should be ready for cutting by mid- to late spring. Keep cutting and it will keep regrowing, but will probably go to seed by late summer so it really depends on your zone as to how long into summer it lasts. In my climate, it goes to seed by start of summer. Because winter is mild here, I sow in autumn and it grows all through winter and then kicks it when it starts getting really hot.

The problem is that they grew in August heat, these are not good crops for July- August. These grow best in cooler mild weather, not hot summer weather and grow better in spring. You can try to grow lettuce in September as the weather cools, but I don't think autumn lettuce is as good to eat as Spring lettuce. You could plant more Arugula seeds now, they should grow better and taste better in cooler weather, they don't take long to grow something before winter.