1. No, in fact that is risky in terms of perpetuating pests/disease... some crops such as strawberries, you should actually do a BURN across your planting spot to eliminate pests and diseases. Generally a rule of thumb in any sort of cultivation, you want to keep dead plant parts away from living plants.

2. Baby powder (talc) is not soluble in water... that would technically be a suspension... but what purpose would that serve? Diatomaceous earth is a more common dust type pest control; it has sharp particles that kill bugs; talc, on the other hand, does not.