They Saved the Peanut Industry

Every year, it seems a different factor is thrown in with this virus, and it’s a challenge to keep it in check. But thankfully, there are people from all over contributing to the management of this virus.

Recalling a visit to a peanut field outside of Tifton, Georgia, in the late 1980s, Timothy Brenneman, Ph.D., University of Georgia (UGA) plant pathologist, says, “I remember walking out of that field scratching my head because this was a new type of beast that we were not used to dealing with.”

Brenneman was responding to a report of an unknown disease infestation. He and Albert Culbreath, Ph.D., a fellow UGA plant pathologist, walked the field but could not identify the disease, let alone the cause. The unknown beast turned out to be tomato spotted wilt virus (TSWV). That day set the stage for a three-decade war between the disastrous disease and a cross-discipline team of researchers, extension personnel and industry leaders. This collaboration brought the Southeast’s peanut industry back from the brink of disaster. The team won the battle, but the war continues.

Detection of Threat to Peanut Industry

First discovered in Texas in 1971, TSWV didn’t pose a significant threat to the rest of the U.S. peanut crop until it moved into the Southeastern peanut states. Severe outbreaks of TSWV in peanuts occurred as the insect vectors for the virus — most commonly tobacco thrips (Franklinella fusca) or western flower thrips (Frankliniella occidentalis) — transmitted TSWV. In some regions of Georgia, peanut fields saw infection rates ranging from an estimated 40% to nearly 100%.

Culbreath remembers that when he began working with Jim Demski, Ph.D., UGA plant virologist, and Jim Todd, Ph.D., UGA entomologist, they suspected the horrendous possibilities of TSWV. “We really didn’t know exactly what the potential damage was,” Culbreath says, as he recalls that first encounter with TSWV. “Ultimately, we suspected it had great potential, and, unfortunately, we were correct.”

The disease spread rapidly, and leaders in the Southeast feared losing the region’s peanut industry, which is a significant economic driver. However, an interdisciplinary team known as the Spotted Wilt Eradication Action Team (SWEAT) rose to the challenge.

Hard Work and SWEAT

SWEAT, an acronym that Culbreath notes is highly fitting when he recalls the team’s long hours in the field, quickly garnered support from Southeast peanut researchers determined to find solutions for the puzzling disease.

“It was not like we all got together and said, ‘We’re going to put this team together to work on spotted wilt,’” Culbreath says of SWEAT’s origin. “Most of us involved recognized the necessity of it [SWEAT], both in terms of the scope of the problem and because, early on, no single project had the resources to achieve the progress we’ve since made with spotted wilt. The teamwork was born out of necessity. We didn't have a choice.”

SWEAT has gone through many changes in the past 30 years, with notable players in the peanut industry pitching in and creating management strategies for the challenges the virus poses each year. Many management strategies developed by the team, such as the discovery of resistant varieties, remain successful today.

Solutions for TSWV

William Branch, Ph.D., UGA endowed seed development professor in peanut breeding and genetics, developed Georgia Green, the first popular cultivar with resistance to the virus. Georgia Green worked in concert with the other practices identified for managing TSWV such as mid-May planting, increased plant population, at-plant insecticide (phorate) application, twin-row-pattern spacing and strip tillage. This integrated approach was critical in reducing disease losses since no single component provided the protection needed. The genetic resistance in Georgia Green was a key component, and peanut breeders in the Southeast responded by developing more cultivars resistant to spotted wilt.

Investments in molecular studies have improved researchers’ understanding of the virus. “But there's still a lot we don’t know,” Brennemen explains, “and in many ways, we still rely heavily on genetic resistance.”

Although management strategies haven’t completely eradicated the virus, research over the last few decades has produced tools to identify peanut disease pressures throughout the growing season.

Risk Index Established 26 Years Ago

The Spotted Wilt Risk Index for peanuts, created in 1996, assigns risk values based on the symptoms of TSWV to determine the most effective integrated approach to manage the virus. Culbreath helped develop the index, but credits Steve "Bug" Brown, Ph.D., UGA extension entomologist, as the “father” of the project. Using the index, now known as Peanut Rx, farmers can determine a field’s disease and TSWV risk level. Peanut Rx was initially developed and is reviewed each year by peanut specialists at the University of Georgia, the University of Florida, Mississippi State University, Clemson University and Auburn University. Today, Peanut Rx helps growers evaluate their risk not only for TSWV, but also for leaf spot and white mold.

TSWV Today

Wilson Faircloth, Ph.D., Syngenta agronomic service representative, explains that, even after all these years, the common challenge for growers managing TSWV in peanuts remains the unpredictable factors that initially cause the disease.

"Last year, some peanut fields had trouble with germination, and that was a big contributor,” Faircloth says. “But this season, seed germination and quality were better, which led to good stands and just a perfect early season. We also had some adequate rains. Then one day we walked out and went, ‘Oh no, what's going on?’ Every year, it seems a different factor is thrown in with this virus, and it’s a challenge to keep it in check. But thankfully, there are people from all over contributing to the management of this virus.”

The day of TSWV’s eradication isn’t here yet, but the progress made so far is a testament to a successful, ongoing collaboration within the peanut industry.