Defending Sweet Potatoes From Fearsome Pests

By Claire Schloemer

Sweet potatoes are beloved for their delicious taste, health benefits, and bright colors, and they are ranked as the seventh most important food crop in the world. Sweet potatoes are grown in tropical and subtropical areas around the world, serving as food, animal feed, and a source for biofuel production. They are also a good pick for a low-input farming style because they are well adapted to sandy soils and drought conditions. In the United States in 2022, farmers harvested over 130,000 acres of sweet potatoes, generating nearly $600 million in revenue, with the southeastern U.S. leading domestic production.

But, beneath the surface, there is more to the story. This resilient crop faces relentless threats from pests and diseases, particularly in regions like the southeastern U.S., where soil and weather conditions also favor its adversaries. In an article published in March in the Journal of Integrated Pest Management, my colleagues Scott Graham, Ph.D., and Kathy Lawrence, Ph.D., and I detail various pests of sweet potato and their management options.

Among the most powerful foes are plant-parasitic nematodes, specifically root-knot nematodes. These tiny parasites attack the root system, causing the formation of galls that diminish the plant’s ability to take up water and nutrients. This results in stunted growth, reduced yields, and unattractive, cracked roots. To make matters worse, these nematodes can interact with other pathogens, exacerbating the damage.

Insect pests also pose significant challenges. The sweetpotato weevil (Cylas formicarius),known for its devastating ability to ruin storage roots, inflicts over $7 million in annual losses in the southern United States. Feeding by wireworms, cucumber beetles, and flea beetles further compromises root quality, leaving growers grappling with economic losses.

Thankfully, farmers have their own arsenal of defenses. The battle begins with selecting hardy sweet potato varieties. Varieties like ‘Covington’ and ‘Bonita’ have shown resistance to southern root-knot nematodes, withstanding nematode attacks better than traditional varieties like ‘Beauregard.’ Meanwhile, newer varieties like ‘Orleans’ are gaining traction for their high yields and robust performance. However, while some varieties can resist most nematode pests, they remain vulnerable to the guava root-knot nematode, a newer species spreading in the U.S. This highlights the need for continued research and breeding efforts to develop varieties capable of opposing evolving threats.

After selecting a sturdy variety, cultural management strategies like crop rotation and cover cropping are farmers’ next line of defense. Taking a year off from growing sweet potatoes and rotating with non-host crops like peanuts or bahiagrass has proven effective in reducing nematode populations. Farmers can also use cover crops to breathe life into the soil between sweet potato cropping seasons. These crops are grown during the winter to improve soil health, suppress nematode populations, and prepare the fields for spring planting. For example, mustard contains compounds called glucosinolates that, when broken down, release substances that are toxic to nematodes. However, farmers must be wary of the “green bridge effect”—when cover crops provide winter habitats for insect pests.

Biological control represents another method of attack against pests of sweet potato. Harnessing the natural properties of microbes can help farmers win the battle against pests. For example, the spores of the fungus Beauveria bassiana infect and kill many types of insect pests, including sweet potato weevils. Biological agents like Beauveria have been formulated into environmentally friendly products to make them more effective and easier for farmers to apply. Similarly, farmers have tapped into the potential of a different type of nematode. These beneficial entomopathogenic nematodes are microscopic animals that parasitize and kill insects—plus, they are effective against sweetpotato weevils and wireworms. We can also use microbes to combat plant-parasitic nematodes. These biological nematicides, like Purpureocillium lilacinum, are gaining attention for their ability to parasitize nematode eggs and reduce their populations. These biological solutions aid farmers in the fight against sweet potato pests while minimizing environmental impact.

Despite advances, questions remain in the war against these pests. Biopesticides, winter cover crops, and resistant varieties require further evaluation to maximize their potential. Research into nematode-resistant cultivars that can also combat the guava root-knot nematode is particularly urgent, as this pest poses a growing threat to U.S. sweet potato production. Developing comprehensive IPM strategies is key to enhancing the sustainability of sweet potato farming. This approach integrates cultural practices, biological control, and selective chemical use to balance productivity and enable natural processes.

Sweet potato’s versatility and nutritional value make it an essential crop for global food security. In regions like the southeastern U.S., its cultivation supports livelihoods while providing nourishment to millions. By addressing its pest pressures with innovative, sustainable strategies, we can ensure sweet potato lives on despite many formidable threats to its production. Although coming face to face with the threats of pest and disease, sweet potato is a resilient crop that is able to defy difficult growing conditions and menacing pests.

Claire Schloemer is a Ph.D. student in entomology at the University of Wisconsin-Madison. She conducted research on sweet potato IPM strategies while earning her master’s degree in entomology at Auburn University. Email: [email protected].

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