We live in Carrot Fly country. I’m not sure why, but it is commonly accepted in Western Washington that you will not grow a decent crop of carrots without some sort of barrier to protect them. (Talking about barrier methods of carrot protection makes me snicker.)
I’ve lost most of my unprotected carrot crops to rust fly. Last year I must have gotten my timing just right because my fall/winter crop was about 80% unblemished, but was also grown in virgin soil. That’s pretty good!
Here’s the culprit: Chamaepsila rosae, the Carrot Fly. This is one pest without an eco-friendlier pesticide option. There is no Sluggo or Bt equivalent for the Carrot Fly. The chemical options I saw for dealing with it were systemic toxins uptaked into the carrot itself. Oh joy, just what I don’t want my kids chewing on. Which is why you go with The Barrier Method, and try to keep the pest off your crop entirely.
My first attempt this year to thwart the Carrot Fly seemed promising: fine mesh fabric, draped over wire hoops and secured with clothespins and a tight rope around the mesh which dangling to the bottom of the raised bed.
Apparently the rope wasn’t tight enough. I don’t know how those bastards did it, but they got in. After I secured the mesh I started to see carrot flies trapped on the inside of the mesh. The first day or so it was a few, but by the third day it was hundreds. It was creepy, that many flies crawling around upside down, right over my sweet baby carrots. This bed had never previously grown carrots or related crops, so these flies got in, they were not born into this bed.