Answer: Fungicidal treatment of bean seed isn't necessary if you plant your beans at the appropriate time (when soil temperatures are above 60F) and are careful with watering. The damping-off fungi need lots of moisture to grow. Even if there's no danger of damping off, large, starchy seeds like beans, peas, and corn can easily rot if there's too much moisture in the soil. If your soil tends to drain slowly, form a hill of soil or a raised bed before planting.
There's another type of "dust" used with legumes -- a bacterial inoculant (Rhizobium species). This dust helps bean plants to "fix" nitrogen from the air and make it available to the plant. Many gardeners wouldn't plant a bean without it, but others don't and their crops are just fine.
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