Mohrs rosinweed

Mohrs rosinweed (Silphium mohrii) is a perennial herbaceous plant belonging to the Asteraceae family. In agronomy, it is classified as a persistent taprooted perennial weed, which is characterized by its ability to store significant reserves in its root system, allowing for rapid regeneration even after attempts at mechanical removal or adverse seasonal conditions.

Native to specific regions in the southeastern United States, this plant typically thrives in limestone prairies and forest openings. Within agricultural environments, it can become a problematic weed in permanent pastures, hay fields, and neglected agricultural land where it competes directly with desirable forage crops or small-scale farming activities.

The biology of Silphium mohrii is defined by its deep, stout taproot system and strong, upright stems. The plant exhibits a vigorous growth habit, often reaching considerable heights during the summer months. It relies on a combination of vegetative propagation via root crowns and significant seed production to expand its footprint in disturbed soil environments.

The economic impact of this weed is primarily driven by its competitive nature for light, water, and soil nutrients. By forming dense stands, Mohrs rosinweed reduces the biomass of surrounding crops, leading to decreased yields and degradation of pasture quality. It acts as an aggressive competitor that can rapidly displace desirable vegetation if not managed proactively.

Effective control measures require a strategic, integrated approach. Mechanical control involves deep tillage to sever the primary taproot, which is most effective during the early stages of development. Chemical control is achieved through the use of systemic herbicides applied during the rosette or active growth stage, ensuring translocation to the root system to prevent regrowth in subsequent seasons.