Companion planting guide › Carrots and onions against carrot fly

Carrots and onions against carrot fly: does it work?

Promising Some peer-reviewed or extension evidence, but limited, conditional or mixed.

Onions reduced carrot fly damage in one field study, but only while onions were young and when onions outnumbered carrots.

1. Uvah I.I.I., Coaker T.H. (1984). Effect of mixed cropping on some insect pests of carrots and onions. (FAO AGRIS record).

Mechanism

Onion volatiles may mask carrot odor and disrupt host-finding by female flies.

What the research found

• Uvah & Coaker (1984): carrot fly damage fell with onion intercropping, strongest with young onions and higher onion:carrot ratios; the effect became negligible once onions began to bulb. French marigold intercropping was ineffective.

Caveats

Narrow window and high onion ratio needed. Row covers are the more reliable control.