Answer: Probably the most common reason for defoliated seedlings is slug damage. Since slugs work at night you don't see them, but you might notice trails of shiny slime in the area. They will hide under mulch or rocks or a similar location during the day. You can control them by a number of methods: sprinkling the soil surface with horticulture grade diatomaceous earth seems to stop the immediate damage, using traps baited with stale beer helps to reduce the overall population. You can also hand pick them at night and drop them into soapy or salty water, or you can spray them one by one with a mixture of ammonia and water (a squirt gun works well).
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