Bill Curran has devoted 18 years to a mystery that’s new to many of us. As lead scientist for Pioneer’s LaSalle, CO, Goss’s wilt hybrid development and screening program, he preaches prevention because there is no remedy.

“Hybrid resistance is the key defense strategy for Goss’s wilt,” Curran advises.He urges growers to scout fields for unusual lesions, and randomly stunted or wilted plants. “Send suspicious leaf samples to a certified university or seed-company laboratory to verify what you have,” he says.

“That part is key because there has sometimes been an overblown assumption that any leaf damage is Goss’s wilt,” says University of Minnesota associate professor 
of plant pathology Dean Malvick. These days he spends a lot of time advising crop consultants and growers on Goss’s wilt. “Everyone wants to know how it became so widespread in two years.

Why has it finally crossed the Missouri River and headed east after first being found in Nebraska in the 1960s? Found in Iowa in the early 1980s, why has it re-emerged in the central Corn Belt after a 30-year hiatus?

For Goss’s wilt to explode the way it has in the Corn Belt, “either something brought it in a big way or we’ve had it at low levels for a few years, and weather conditions and increased corn on corn production now fuel its development,” Malvick says.

“Clearly, our farming practices have played a role in the recent outbreak of Goss’s wilt,” says Alison Robertson, Iowa State University Extension plant pathologist.

She describes the perfect storm for Goss’s wilt: Hundreds of thousands of acres of susceptible germplasm. “Add to that warmer temperatures, more continuous corn and high-residue environments hospitable to overwintering inoculum. We’ve done a lot less tillage the past two years,” Robertson says.

“It’s getting wetter in our part of the world, which is more favorable for bacterial production and infection,” Robertson says. “Rain spreads those pathogens. We’ve also had more severe weather. Goss’s wilt requires plant injuries to inoculate the plant with disease.

The earlier in the growing season the disease occurs, the greater effect it will have on yield. Generally, the earlier the infection the greater the risk of a significant yield loss. The bacteria grow inside the plant once the infection has occurred. It doesn’t matter when in the growing season plant injury occurs: “Anytime we get injury, we can get infection if the bacteria is present, Robertson says. “In Nebraska young seedlings can get Goss’s wilt from sandblasting.  If we have a hailstorm come through mid-grainfill, we could get Goss’s wilt."

 The Goss bacteria (Clavibacter michiganensis subsp. nebraskensis, or Cmn) can spread from field to field in rain droplets or on windborne soil particles and residue, Robertson says.

 

Prevention

“One prevention measure is burying your residue with more aggressive tillage. Yet, if you do that but your neighbor doesn't, you could still be at risk for Goss's wilt. We hope to collect more data on this in the next growing season,” Robertson says.

Malvick adds, “There’s minimal evidence that more aggressive tillage will make a big difference in avoiding Goss’s wilt in a particular field, yet people do it because it’s something they can actually do that might make a difference.”

Weed control, especially of grasses, is also vital since grasses are alternate hosts,” Curran says. barnyardgrass, for example, is an alternative host.

But your first line of defense is selecting resistant hybrids and rotating with non-host crops.

One challenge in hybrid selection is the lack of a universal resistance scale across seed companies, Malvick says.

Sprayer damage is what Pioneer Agronomist Jerome Lensing suspects first introduced Goss’s wilt on one farm near Hastings, MN. “Plants were damaged where the sprayer turned around, and then some severe weather splashed the bacteria on the damaged plants.” He speculates that Goss’s outbreaks in other areas are from the movement of residue from infect fields via equipment similar to how weeds and SCN have been spread.

“There’s a lot of concern about Goss's in the countryside, but we really can’t predict what will happen in the future,” Minnesota’s Malvick says. “There is no way to predict what the risk is this year. Weather is part of the equation, like having a lot of rainfall and severe weather through late-July. And the more of the disease already in a field or area the previous year, the higher the risk is. But we don’t really understand all the factors.”

There’s a fine line between vigilance and hysteria, says Pioneer Agronomist Lensing. “I know one grower who reduces his Goss’s risk by burying the residue with tillage, only to have a less vigilant neighbor’s chopped stalks blow onto his fields, potentially contaminating his fields with that blown residue. And then other growers don’t scout so they don’t know if they have a problem till way late in the game.

“I walk a line between too much awareness and not enough, depending on whose farm I’m on.”

 

What we know about Goss’s wilt

  • The Goss bacteria (Cmn) spreads by wind, residue movement or with tillage implements. Infection occurs when the plant is wounded and the bacteria splash onto the plants from infected residue.
  • Disease severity is related to May and June average daily temperatures and rainfall.
  • The optimum temperature for bacterial growth is 81° F. Recent warmer temperatures may explain part of the increased incidence of Goss’s wilt.
  • Stress in a field can cause the disease to act more aggressively.
  • It can wipe out a field of corn.
  • There are very susceptible hybrids and very tolerant hybrids.
  • An infection early in grain fill can reduce yields by 50+%.
  • It has a systemic wilt phase and a more common and damaging leaf blight phase.
  • Goss’s wilt bacteria on surface crop residue can survive for at least 10 months.
  • Pure cultures of the bacterium in soil only survived for two weeks or less. However the bacterium survived for at least 10 months in infested surface crop residue. When the crop leaves, stalks, cobs and ears were buried at 4 in. or 8 in., the bacterium was only detected in stalk residue after 10 months.
  • Rotating to a non-host crop, such as soybeans, allows time for infested residues to break down and inoculum levels to decrease. Also, heat, competition with other microbes and low pH reduce the bacteria’s survivability.
  • These weeds are known secondary hosts of Goss’s bacteria: green foxtail, shattercane, sudangrass, barnyardgrass and eastern gamagrass.
  • These species are resistant to Goss’s wilt infection: oats, wheat, sugarbeet, barley, bromegrass, orchard grass, crab grass, proso millet, yellow foxtail, Johnson grass.
  • Seed transmission of Goss’s wilt is not very common. One study found only one naturally occurring transmission in 12,864 seedlings.
  • It develops on the tops of plants.
  • It is most commonly transmitted at growth stage R5 or later.
  • University of Nebraska research found 19% of newer Goss’s wilt isolates have changed compared to older samples of the bacteria.
  • Our most reliable control tools in the meantime are:

          A resistant hybrid

          Crop rotation

          Residue management

–Courtesy of Iowa State University Extension Plant Pathologist Alison Robertson and Bill Curran, Pioneer lead scientist for its Goss’s wilt hybrid development and screening program