Bean Fly (Bean Stem Fly)

Ophiomyia phaseoli

Small shiny black fly whose maggots tunnel down seedling stems. Worst in the first 3 to 4 weeks after the seedlings come up.

Background

Adults are about 3 mm long, shiny black with clear wings. The larvae are cream maggots with dark mouthparts that tunnel through the stem tissue, which weakens seedlings and can kill them. Seedlings are most at risk for 3 to 4 weeks after they come up. It is most common in tropical and subtropical coastal regions and is generally not a problem inland. Weeds and volunteer plants in the legume family can carry it between crops.

How to identify

• Adults: about 3mm, shiny black with clear wings
• Larvae: cream-coloured maggots with dark mouthparts, about 3mm, tunnelling in the stem
• Seedlings yellow, droop or die in the first 3 to 4 weeks, with swelling and cracking at the stem base

Affected vegetables & crops

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Climate zones at risk

Prevention

• Clear weed hosts such as phasey bean and volunteer legumes before sowing
• Do not plant beside an older crop of beans or other legumes
• Sow a little thicker to allow for losses
• Hill soil up around the stems 2 to 3 weeks after the seedlings come up, and mulch, so damaged plants can root from the stem
• Check seedlings twice a week and act if you find more than one larval tunnel per plant
• Dig in, bury or burn crop residue after harvest

Know when Bean Fly (Bean Stem Fly) is actually about

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