The Barrier Method Of Carrot Protection

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.

I sure as hell wasn’t going to open up the mesh and let them out – I’d rather know where the enemy is, even if I don’t want her there – and at that point it was pretty clear that that carrot crop was toast. I’m just letting the flies expire naturally in the carrot bed – most seem dead at this point so I think we’re close. I’m considering that bed a catch crop and will yank all the carrots before the maggots can hatch, starve them and hope to seriously disrupt future population levels.
Meanwhile, I knew I had to replant, and fast. Homebrew Husband pulled out a Garden-Spouse-Of-The-Year move and made me new, more form-fitting carrot protection (again with the snicker) with some scrap lumber we had lying around (Total Cost: $0). And he did this on Father’s Day, as if he needed extra bonus points.
As you can see the new structure is a simple wooden frame designed to fit inside our 4’x8′ beds. We covered the whole thing with mesh netting and secured it with staples. The mesh overlaps to avoid any holes and aprons-out at the bottom so it can be covered with dirt to create a secure seal at the bottom.

My only concern with this new barrier is access for weeding, etc. We’ll see how it works. What have you tried to grow a decent crop of carrots? Any tips on what to do and what to avoid?


  1. says

    geez, all fer the love of carrots. gardening is so crazy.
    did you put compost on that bed? could your compost have been carrying the eggs from last years carrot fly crop? that has happened to me in alaska with slugs, i think. under plastic hoop covers. total bummer. i thought i'd be keeping slugs out and warming things up all in one deft maneuver. instead i had the worst slug problem ever, and i think they were from compost, hatched and then just trapped in there. ick.
    good man, that home brewer. i sure did enjoy his father's day post. building carrot screen enclosures is just too much. tell him to knock it off or you're going to get spoiled and ungrateful.

  2. says

    We also have radish root maggots. Me, right after I seed I dust on a combination of fireplace ash and diatomaceous earth, in a good thick layer over the top of the damp soil. Then I put on a layer of lightweight white fabric barrier, low over the tops of the carrots and radishes. It's stapled to one side of my raised beds, then on the other side it's secured with long strips of wood that hold it tight to the ground. Raised beautiful root veggies that way last year. Works to deter leaf miners, too. I leave more fabric than needed, so as they get taller I just loosen it a little so there's enough to allow the plants to stand up straight.

  3. says

    Absolutely nothing. If I've seen a rust fly I couldn't pick it out from the other flies I've seen. I do try to rotate my carrot crop, but that means the new bed is 2 feet away.

    Frankly I haven't seen any carrot damage. This year there were no new carrots, but I will plant now for Fall. Good luck with your pest problem. We all have them, some have organic solutions, others elaborate protection schemes. Great work Nick!

  4. Cathy says

    To protect carrots, I use a floating row cover that I buy from West coast seeds or Lee Valley tools. You lay it over the bed and push the cover's edges down under the soil all around the border of the bed. If your soil is loose and fluffy, you can just use your hands and it takes 5 minutes or so to do. You can reuse the cover if you're careful not to tear it.

  5. Mary W. says

    Did your barrier method work, or do you find the fall planting is the best prevention? I have terrible problems with carrot maggot, and am close to giving up.

  6. Nancy Sutton says

    Yeah, I ditto Mary’s question…. so, how’d it go? for spring planting? summer-for-fall planting? weeding? And, thanks a big bunch! ;)

    • says

      Ah….how did it go? The mesh tore into a zillion pieces (wind? cats? chickens? rodents? I don’t know) and then my cats decided that bed was their most favorite place in the whole world to sit and soak up sun. In short: I am still looking for my maggot-free carrot salvation, and if I find it, I swear I’ll share. Man I hate those teeny little flies. Grrrr.

  7. Nancy Sutton says

    Okay, so glad you’re on it, too … the flies’ days are numbered ;) With my woodchip mulch, I’m also raising many generations of seedling-devouring pillbugs. I’m going to try religious trapping/removal with overturned melon, orange, apple halves… hmmm ;)

    Sooo…. maybe you could do the 18″ (or 24″ ?) high fly barrier… they’re not supposed to go any higher ;) You could staple something tougher on the sides of your lovely… and ‘loving’ ;)… ‘carrot frame’ …. even 6 mil plastic might work and survive the ‘shredders’ (maybe an outer ‘protection’ of 2×4″ wire (I’m sure you have some scraps lying around :) For the cats, two or three or four (or more?) catnip plants, also protected, but “sacrificed” one at a time, to distract the felines. (They recover from the ‘nibbling’ pretty quickly ;) Might be able to ‘bend over’ the fence for weeding? Or reaching with a stirrup hoe, or shortish collinear hoe? Or, let ‘em duke it out ;)

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