What are these little black bugs on my arugula in Denver CO?

Question

There are little black bugs slowly eating away my Arugula. I live in Denver CO. The weird thing is, we have a pot of Arugula ~50ft away from where the other Arugula is planted and it's completely fine. The plants are watered using micro-sprinklers twice a day. The soil was mixed with compost from a local ranch (horse manure).

My only hypothesis is the weeds growing in the planting area (crab grass and purslane, which we are struggling to keep up with) are somehow attracting the bugs.

Any ideas on what we can do to eliminate these bugs?

Answer 1

These are possibly flea beetles. They enjoy warm dry weather and particularly like brassica crops of which of course arugula is a member. So one way to reduce the attacks is to sow as early as possible during cool and wetter conditions. One thing to try is to sow radishes to try to attract them away from the arugula, they might just like the disposable crop better.

I remember one year the spring was particularly dry here and the population exploded; no matter what I tried, irrigation, covering, nothing seemed to work until the weather broke and the rain put an end to their fun. The early leaves were quite damaged but the plants went on to produce new green leaves later in the season.