Field Surveys of Bush Lima Bean Reveal Shortcomings in Weed Management

To understand the scope of weed problems in commercial lima bean (Phaseolus lunatus L.) production, lima bean fields were surveyed for weeds that escaped control near the time of crop harvest (hereby called residual weeds) from 2019 to 2022 in the Mid-Atlantic and the Midwest, two major production regions of the United States. Overall weed abundance was determined based on relative density, frequency, and uniformity throughout surveyed fields. Density was the number of individual plants in overall quadrats in fields with that weed. Frequency was the number of fields with that weed species recorded in overall surveyed fields. Uniformity was the number of quadrats with a particular weed species in overall quadrats. Approximately 52 weed species were observed, and differences in weed communities were observed between the Mid-Atlantic and Midwest regions. Significant weeds in the Mid-Atlantic region included common chickweed [Stellaria media (L.) Vill], amaranth species (Amaranthus spp.), and morningglory species (Ipomoea spp.). Significant weeds in the Midwest region were foxtail species (Setaria spp.), common lambsquarters (Chenopodium album L.), and amaranth species. Crop management practices used in the fields were obtained from collaborating farmers and vegetable processors. Widely adopted mechanical weed control methods included spring (preplant) tillage and interrow cultivation. Common herbicides included preemergent applications of S-metolachlor and halosulfuron-methyl. Bentazon was the most common herbicide applied postemergence. Classification and regression tree modeling were used to determine linkages among residual weeds and management factors. Despite the adoption of multiple chemical and mechanical weed control methods, this survey revealed extensive weed problems in many production fields. Greater diversification of integrated weed management systems is needed, especially for the control of amaranth species. This survey will help guide future research efforts for weed control in lima bean production.