How to spot it

Seedlings pinch in at the soil line, go thin and dark there, and fall over. Or seeds rot before they come up. White mold may grow on the soil.

What it does

It kills seedlings, usually in their first week or two.

What to do now

• Throw out sick seedlings and their mix; don't reuse it.
• Let the surface dry between waterings and run a fan for airflow.

Keep it away next time

• Use fresh seed-starting mix and clean trays (rinse used ones in 1 part bleach to 10 parts water).
• Water from below and keep the mix moist, not soggy.
• Give bright light and warm soil so seedlings grow fast.
• Thin crowded seedlings, and sow outdoors only when the soil is warm enough.

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Plants it affects

Almost any plant, especially seedlings.