Coping with Carrot Root Fly

Organic carrots are one of the organic movement's big selling points. They simply taste so much better than those grown with chemical fertilisers. Generally speaking they are easy to grow. You do need to keep them weed free but growing them in deep beds in rows that are 10 cm apart so that the foliage makes its own mulch sorts that problem out. The soil needs to be fertile but should not have received any manure or compost for 12 months or the roots will fork; giving interesting results that may look comical but are difficult to prepare for the kitchen. It is best to sow them thinly - and I mean thinly - aim for one seed every 2 cm or so. This cuts down on the need to thin.

The big problem I have with growing carrots is the pest carrot root fly (psila rosae). These little flies lay their eggs on the carrots and the larvae burrow into the roots making them pretty useless and inedible. The flies are difficult, if not impossible, to get rid of as you need to remove not only all carrots but also all members of the carrot (umbelliferae) from your garden and surrounds. That means parsnips, parsley, various herbs such as perennial fennel and angelica; essentially not a realistic solution.

The carrot root fly hunts initially by smell and once it is within range of the carrots it hunts by sight. It flies close to the ground - below 60 cm or so. This gives two defence strategies. The first is to confuse the smell by companion planting. You need to grow a barrier of onions or chives around your carrots. If you have a big plot of carrots it is a good idea to intersperse the carrot crops with breaks of onions. This method has met with some success although not in my garden. From what I hear it works sometimes but if some flies get in then your crop is finished. And once they are in you have got them.

The other, and I think more reliable method is to use a physical barrier. Some people erect a screen around the crop about 60 cm high. They use plastic sheeting or fine mesh. This method is actually more reliable than the companion planting method. However, it is possible for a gust of wind to blow some flies over the top and there you go again - no carrots.

After years, of poor or no crops I have resorted to completely enclosing my carrots. I have used garden fleece and enviro-mesh. These fine coverings keep the flies out but let the air and rain in. Both have been almost 100% successful. I guess there has been a hole or when I was taking a peek one of the little creatures slipped in - I don't know really. The point is it is nearly fool proof. It does have to be a complete seal and you do have to minimise lifting the covering. If you have to weed it is best to do it when it is raining as the flies go to ground and the rain keeps the smell of carrot down too.

So, if you have lost your crops to the root fly give this method a try and you can be enjoying your own buttered baby carrots, carrot salad or vichy carrots once again.