Improving plant-parasitic nematode management with crop rotation and cover crops in sweetpotato production.

Commodities

Practices

This 3-year project will evaluate how integrating crop rotation and cover crops influences plant-parasitic nematodes and soil health in sweetpotato production. The U.S. is one of the major producers of sweetpotato in the world, with over 148,200 acres and a value of over $600 million (USDA-NASS, 2024). Sweetpotato growers suffer from increasing plant-parasitic nematode problems, especially root-knot nematode (Meloidogyne spp.) and reniform nematode (Rotylenchulus reniformis). Current nematode management heavily depends on chemical control, which is expensive and not safe to operate. An economically viable and integrated nematode management program is desperately needed by sweetpotato producers.

Reniform nematode is a severe threat to sweetpotato production in the southern region of the U.S. (Overstreet 2013). It can cause reduced storage root size, cracked tubers, and lead to reduced marketable yield (Abel et al., 2007). Different from the southern root-knot nematode, there are no reniform nematode-resistant sweetpotato cultivars available. Recently, several reniform nematode-resistant cotton cultivars entered the market, suggesting that sweetpotato-resistant cotton rotation may be a profitable system for managing reniform nematodes in sweetpotato production. Besides commodities, some growers are interested in adding a specialty crop to their rotation. Unfortunately, reniform nematode has a wide host range; most specialty crops, including leafy greens, cucurbits, beans, and peas, are all hosts, making it difficult to find a good rotational crop that can bring a good economic return for growers. Sesame is a viable crop in Mississippi and a poor host to reniform nematode. Demand is rising for products such as hummus, baked products, and pharmaceuticals, which has intrigued increasing interest for growers.

Besides crop rotation, cover crops can be useful in integrated management as well. Growers use cover crops for multiple purposes, including pest and weed suppression, soil fertility improvement, and soil erosion control (Kaspar et al., 2011). Cover crops can be useful in nematode suppression if a cover crop is a non- or poor host to the targeted plant-parasitic nematode, or if a cover crop is a trap crop that can be destroyed before nematode reproduction (Wang et al., 2008). Cover crops can also reduce soil erosion and increase soil water-holding capacity. Cover crops can contribute to both weed and pest suppression to deal with increased temperatures. However, the host status of some cover crops to reniform nematode remains vague and needs further investigation.

The overall goal of this project is to (1) Assess 16 winter cover crops host status to reniform nematode in a greenhouse trial, (2) Investigate the integration of crop rotation and cover cropping in suppressing reniform nematode and improving sweetpotato yield in field studies, (3) Conduct on-farm trials testing the integration of crop rotation and cover cropping in both organic and conventional sweetpotato production systems, (4) Evaluate economic profitability of integrating crop rotation and cover cropping in sweetpotato production.

Objective 1. Determine the host status of selected winter cover crops for reniform nematode under greenhouse conditions.

This objective aims to systematically evaluate the host suitability of 16 winter cover crop species commonly used or potentially adaptable to the Mid-South region. Because the effectiveness of cover crops in nematode management depends largely on their host status, identifying non-host or poor-host species to reniform nematode is essential for designing suppressive systems. Existing information on reniform nematode host status is limited and often inconsistent across studies, particularly for newer or regionally adapted cover crops. This study will provide standardized, comparative data across plant functional groups.

For this objective, our hypothesis is: Winter cover crop species differ significantly in their host status to reniform nematode, and this variation is associated with plant functional group, with legumes and brassicas exhibiting lower nematode reproduction factors (Rf) than grasses and susceptible broadleaf species.

Objective 2. Evaluate the effects of crop rotation and cover cropping on reniform nematode suppression, soil health, and sweetpotato productivity under field conditions.

Integrating crop rotation and cover cropping is an agronomically sound production system, but work is needed to determine how well it manages reniform nematode. Reniform nematodes persist in the soil profile and affect crop yield. We will determine how effectively crop rotation and cover cropping manage nematodes throughout the soil profile. Soil is a living ecosystem with many microbes that contribute to soil fertility and productivity over time. This objective aims to assess the combined effects of crop rotation and cover cropping on nematode population dynamics, soil health, and sweetpotato performance under field conditions. This objective will be investigated in replicated, long-term plot-scale research as well as on-farm trials. Conducting this study at a research station allows for controlled implementation and consistent data collection across treatments. We will determine if rotation and cover cropping help suppress reniform nematode population densities, improve soil health, and increase sweetpotato yield.

For this objective, our hypothesis is: Crop rotation with poor- or non-host crops combined with winter cover cropping will significantly reduce reniformis nematode population densities, improve soil health indicators, and increase sweetpotato yield compared to continuous sweetpotato without cover crops.

Objective 3. Validate integrated management strategies through on-farm trials.

This objective focuses on validating research findings under real-world production conditions through collaboration with growers representing both organic and conventional systems.

Objective 4. Evaluate the economic profitability of integrating crop rotation and cover cropping in sweetpotato production.

Producer adoption of integrated nematode management practices ultimately depends on economic viability. This objective quantifies the full economic costs and benefits of each crop rotation x cover crop treatment tested at the MSU North Mississippi Research and Extension Center (Objective 2) and on all three cooperating farms (Objective 3), benchmarked against continuous sweetpotato monoculture. This component will be studied using an enterprise budgeting framework that captures transition costs, input savings from reduced nematicide use, revenue from rotational crops (cotton, soybean, sesame), and changes in sweetpotato yield and grade distribution. This objective directly addresses SARE's long-term profitability pillar and will produce practical decision-support tools growers across the Mid-South can use to evaluate these practices for their own operations.

Objective 5. Share research findings and collaborate with stakeholders through Extension efforts.

This project includes a comprehensive plan for disseminating research findings and actively engaging stakeholders. Research results will be shared with the scientific community through peer-reviewed publications and presentations at regional and national conferences. To ensure practical impact, findings will also be translated into accessible formats for growers and other stakeholders through Extension activities.