Combining biological control and winter cover cropping to mitigate insect damage in organic sweet potatoes

Insect pests pose a significant challenge for organic sweetpotato producers in the Southeast. These pests include the WDS complex, which is comprised of wireworm, Diabrotica, and Systena species, sweetpotato flea beetle (Chaetocnema confinis), and sweetpotato weevil (Cylas formicarius). These insects cause damage that reduces the yield, quality, and marketability of sweetpotato roots. However, there is a lack of knowledge of effective organic integrated pest management practices for sweetpotatoes. To combat this, we established field trials in Brewton, Alabama and Dobson, North Carolina to test the efficacy of selected winter cover crops in the suppression of belowground insect pests and plant-parasitic nematodes. This was accomplished by planting sweetpotatoes into the footprints of selected winter cover crops. Additionally, we applied three species of entomopathogenic nematodes (Steinernema feltiae, Steinernema carpocapsae, and Heterorhabditis bacteriophora), the biological product Majestene, and the insect pathogen Beauveria bassiana to half of each plot to determine their combined ability to suppress insect pests and reduce insect damage. Upon harvest, marketable yield and incidence of insect damage of sweetpotato roots were determined. Ultimately, we found that a winter cover crop mix of crimson clover, daikon radish, elbon rye, and wheat was associated with high marketable yields, low insect damage, and low plant-parasitic nematode populations. Results of the application of biological insecticide products were mixed, indicating low efficacy.