University of Florida study helps farmers find best fields for sweet potatoes

Wireworms won’t dampen the spirits of Florida’s sweet potato growers, thanks to ongoing research by scientists at the University of Florida’s Institute of Food and Agriculture Sciences.

Wireworms took center stage in Florida after some major sweet potato growers converted fields previously dedicated to grain crops to the sweet potato crop. Some acreage was initiated by a farm that had actually relocated to Florida after leaving California because of prolonged drought, hopeful to take advantage of Florida’s warm weather, abundant water resources and sandy soil.

Although North Carolina claims the title of sweet potato giant in the nation, Florida’s early warm springs gives the state’s growers an edge in planting—and cornering the early market for sweet potatoes. Earlier harvest means early arrival in the nation’s major grocery chains.

Wireworms live in the soil. Photo: S. Southern, NCSU

But when several growers noticed worm tunnels in their sweet potatoes, wireworms climbed to the top of the pest management priority list. Damaged sweet potatoes couldn’t be sold as fresh market produce, the most profitable market.

“Growers told us specifically that if we couldn’t solve the wireworm problem, they couldn’t make a profit in Florida,” said Robert Hochmuth, University of Florida Extension Agent and Director of the Suwannee Valley Agricultural Extension Center in Live Oak.

Repeated use of the major insecticide appeared to have begun to cause insecticide resistance in wireworms. Growers had only a few insecticide and several cultural pest management options available. Since wireworms had not previously been a major pest in North Florida, little research had been done on their prevalence or the pest management options that worked best.

Hochmuth and Florida IPM Coordinator Norm Leppla used funding from a Southern IPM Center IPM Enhancement Grant to test various trapping mechanisms on the Extension center in Live Oak to find a consistently effective trap. Several growers, eager to help solve the problem, also volunteered their fields for the study.

The first step involved determining the wireworm species present and the risk of wireworm populations in a field. Hochmuth and Leppla placed their traps in a field where sweet potatoes had not yet been planted.

“We were trying to predict whether the field would be at high risk for wireworms, to help them avoid infested fields,” said Hochmuth.

Hochmuth and Leppla also created a database of all sweet potato farms in Florida, to expedite communication among farmers.

The most challenging piece to the research was the fact that wireworm populations were not consistent in an area. Some farms would have several fields with no wireworms and two or three fields—in between clean fields—with major infestations.

The trapping gave Hochmuth the information he needed to tell a farmer which fields were safest for sweet potato planting and which were not.

“This is a new problem, so we’re trying to stay ahead of the curve,” said Leppla. “We’re doing prevention, which is a major component of IPM.”

The trapping project gave farmers the information they needed to continue confidently farming sweet potatoes—how to avoid an initial wireworm infestation. Now Leppla and Hochmuth are using a new Florida Specialty Crop Block Grant to continue to the next phase—finding ways to manage the pest for the long term.

To stave off resistance to the only insecticide that controls wireworms, the researchers are examining other management options, including cultural control and biological control, in addition to insecticide application timing to manage wireworm numbers without risking development of resistant wireworm populations.

For now, Leppla and Hochmuth have confronted their imminent crisis. Their goal is to prevent any future recurrence.

“We want to help them stay in business,” said Hochmuth. “When they don’t have success with an insecticide, we can now offer them some assistance.”

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