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Identification
Small dark fly whose larvae tunnel inside bean stems near soil level; entry marked by tiny yellow-brown puncture spots on leaves.
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Life Cycle
Adults lay eggs in leaf tissue; larvae mine down into the stem to pupate; several generations occur through the growing season.
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Damage Signs
Larval tunnelling girdles the stem base, causing wilting, stunted growth, and seedling death, especially in young bean plants.
healing
Treatment
Remove and destroy affected seedlings promptly. Mound soil around stem bases to encourage secondary rooting above the damage.
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Prevention
Rotate bean crops, avoid early-season planting stress, and use fine mesh covers on young seedlings.