Alternaria has infected the pods of many hailed crops. (See photos below.) Keep watching these crops. When infected areas make up 50% or more of the crop, swathing early may be the best way to salvage the yield in those infected plants if a large proportion of pod surfaces are covered with the black spots. Otherwise diseased plants will shell out if left standing while you wait for healthy plants to be ready. If healthy plants are showing some color change or if the seeds are at least firm, they should mature in the swath.
Click here for an older article with more harvest management tips for diseases and damaged crop.