Growing Carrots: Beating the Carrot Fly

The bain of growing carrots in my garden has always been the Carrot (rust) Fly.  From late summer and through the winter storing, my carrots had suffered the brown holes and bruised markings from the maggots of the carrot fly.  The damage would get worse as the season progressed and eventually these number 3 carrots would be totally unusable.

Over the many years I’d tried a number of things to alleviate the problem.  In the ‘80’s I tried some polyester row cover.  It was too light and tore easily.  I then went to wooden frame panels with window screen vinyl.  That started out better but soon I had aphid buildups with no way for the ladybugs to get at them.  I had to abandon these frames. 

Another year I’d heard if one had wild carrot growing nearby, the carrot fly would be attracted to that instead of your carrots.  I even brought one wild carrot plant (free of soil) over the USA border with me from just a few miles away.  That didn’t work either.

For several years I just didn’t grow carrots.  When I finally started back up I did quite well for the first couple of years and then it all came back.  I tried different landscape fabrics between the rows.  And heavy leaf mulches.  Nope.

Finally, about five years ago, my son TOG was talking with a fellow grower at the local farmer’s market.  He asked what they did (organically) for Carrot Fly.  The fellow said: “Oh, you don’t know?”  and then explained they always rotate their carrots in the beds between their long hoop houses.  It turns out the fly can’t fly higher than 2 feet and they set up a barrier at the ends of the beds that are sandwiched between the hoop houses, blocking the access to the flies.

The barrier can be made of anything: plywood, row cover polyester, screening, black or clear plastic.  It just has to physically block the way for the flies. 

And so I built my first four Carrot Frames to surround my carrot beds.  Made of ripped 2 X 4’s and 2 X 2’s and stapled on old pieces of clear greenhouse plastic, I’ve surrounded my carrot beds and have had good success for three years.  Until last year.

Last year had a few extra variables.  In the rotation, my carrots follow the greenhouse.  That means every other year the carrot frames must butt onto my new, larger greenhouse.  And I need to be able to open the northern doors of the greenhouse for ventilation which then open into the carrot beds.  I had constructed a screen door for the greenhouse that was 3 feet high but somehow the flies still got in.

I did have one side of my carrot frames that was only 2.5 feet high plus I wasn’t as careful with anchoring the plastic at the bottom of the frames.  Perhaps they went over or under the plastic?  Also, I now till old leaves into the bed before planting.  Could I have used leaves that had been sitting on the previous carrot bed all winter that contained eggs or larvae that infiltrated the new bed?

This year I’ve battened down the hatches (of flies).  The frames are not next to the greenhouse and I raised my one shorter frame to 3.5 feet like the rest.  I’ve weighted down the 6 inch plastic skirts on the paths and on the surrounding lawn.  I made sure I had virgin, aged leaves for digging into the bed. (Remember, those leaves tilled in increased my poundage by 50%).

For the winter and spring, I store my carrot frames against the back fence.  To set up I just wash them, screw them together in their corners and wrap and staple the extra plastic at the corners.  To access the beds, I step over the frames using two 5-gallon pails as stile steps.  For weeding and maintenance and reaching the outer half of the beds, since I only have one centre path, I have a nice, portable, plank “bed bridge’ that spans a bed so I can get at all of the two 50 square foot beds without stepping in them.

 

This year I was surprised with the poorer germination of my carrot seed.  This June was exceptionally cool and I may have covered the furrows with a bit too much sifted soil.  It wasn’t the older seed since I did some rows with my brand-new seed with the same result.  Thankfully, I got enough growing to fill most of the rows.  Although it is nice to have the option of thinning the weaker seedlings out – just not this year.

TOG uses a set of hoops with some polyester row / bed cover to cover his carrot beds to keep the fly out.  It seems to work for him.  I’m hoping this year’s changes will solve last year’s glitch.  There’s nothing like bright, clear, clean carrots fresh from the garden all winter until April.

Happy Gardening.