Approaches to Organic Sweetpotato Cultivation: Managing Nematodes, Insects Pests, and Soil Health with Winter Cover Crops and Biopesticides

Claire Schloemer¹Scott Graham¹Koon-Hui Wang²Brent Sipes²Bisho R. Lawaju¹Kathy S. Lawrence^1*

• ¹Auburn University, Auburn, United States
• ²University of Hawai'i at Manoa Hawaii Research Center for Futures Studies, Honolulu, United States

Growing demand for organic sweetpotato production underscores the need for sustainable pest management and soil health strategies. This study evaluated six winter cover crop systems followed by summer sweetpotato, with and without biopesticide applications, to manage Meloidogyne incognita and insect pests while assessing soil health indicators. Marketable yield was highest after wheat (20,679 kg/ha), exceeding the fallow treatment by >2,000 kg/ha. Biopesticide use further increased yield (+700 kg/ha), reduced insect damage by 36–40% (P ≤ 0.05), and enhanced crop value by $33/ha. At planting, M. incognita densities were similar across treatments, but by midseason they were lowest following rye. Wireworm damage did not vary by cover crop, though biopesticides provided significant protection. Cover crops also shaped nematode communities, with crimson clover, wheat, and mixed systems supporting higher structural index values later in the season, while enrichment index and fungal-to-bacterial ratios remained unchanged. Soil microbial respiration peaked at planting, especially after wheat and the cover crop mix, and microbial biomass increased across all cover crop treatments, with rye supporting the highest growth. Radish and wheat showed trends toward lower M. incognita populations and greater economic returns, though effects were not statistically significant. Canonical correspondence analysis revealed nematode communities, microbial abundance, and soil CO₂ flux as key drivers of yield. In 2022, yield was negatively associated with M. incognita but positively correlated with fungal-to-bacterial and GP:GN ratios; by 2023, yield was instead negatively associated with fungivorous nematodes and microbial respiration, and positively with protozoa biomass and protozoa-to-bacteria ratios. Overall, combining cover crops with biopesticides improved yield, reduced pest pressure, and enhanced soil biological function, demonstrating a promising strategy for sustainable organic sweetpotato production.