What follows is from the Kentucky extension service. These moths devastated my two baptisias last year - I cut them to the ground and to my surprise they have come back just fine.
Genista caterpillar larvae (nocturnal moths) lay their eggs in spring; they hatch begin feeding on the tender new baptisia plant growth. The larvae work fast and can completely strip the foliage of a mature baptisia in a few days...fortunately, this shouldnâÂÂt cause permanent damage to the plant. The larvae have 5 stages before they pupate for overwintering. Since the moths are quite prolific, they can actually lay several generations of eggs each year, so youâÂÂll need to monitor your baptisias all summer. When the caterpillars are young they can be easily killed with organic BT (Bacillus huringensis) products.

Seems like you would see chewed leaves if caterpillars were working on it. When any plant has leaves turning yellow then black I always suspect too much water or poor drainage. If you are over watering or getting lots of rain that could be the cause. They do like moist soil but again, too much water is a problem. If its drainage issues, the roots could be suffocating/drowning from lack of oxygen. Often an overwatered plant looks like it needs more water because the leaves wilt just like when a plant is too dry so it can be confusing what to do.