Blossom drop in beans is usually an environmental problem. The causes include: high temperatures, over 90°F; soil moisture too low.
Solutions - plant early in the season so the temperatures are more moderate; pick the pods regularly to encourage more fruit set; do not let the soil dry out between watering.
Read more about managing problems with beans.
If you notice holes in leaves, skeletonized areas on leaves, or chewed leaves, you might have Cucumber beetles on your bean plants. Adults also feed on blossoms.
Solutions - management is difficult. Place protective cloth over young plants until they are large enough to withstand some damage.
If you notice that your bean seeds rot in the ground and do not sprout, or if the bean seedlings collapse soon after they come up, then the problem likely is a soil fungal disease known as Damping off.
Solution – plant bean seeds when the soil temperature is moderately warm, about 60°F or higher. Do not overwater.
Read more about planting dates for beans.