Drought and extreme heat in 2012 detoured what could have been another bad year for Goss's wilt infestations in Nebraska corn. But heed this warning from Tamara Jackson-Ziems, University of Nebraska-Lincoln plant pathologist: "Don't let your guard down."
The disease continues its march east and north in the Corn Belt and has become one of top disease pests of corn.
It first became prevalent in Colorado and western Nebraska in the 1970s and 1980s, but from the late 1980s to 2006 it resurfaced only sporadically. Then, according to Jackson-Ziems, it returned in western Nebraska and parts of Colorado and Wyoming in 2006, then quickly spread east, and two years later it was detected as far east as Indiana. "It now has been found in 13 Midwest states and two Canadian provinces."
Yield losses in heavy infestations have been reported as high as 100 bushels an acre.
Since Goss's wilt is caused by a bacterium, fungicide applications are not effective.
Jackson-Ziems and her plant pathology colleagues recommend planting corn hybrids that carry resistance to Goss' wilt as the best management strategy. About 30 companies marketing corn hybrids in Nebraska publish ratings for Goss's wilt resistance, she says.
She points out that the bacterium survives in corn residue, so rotations to soybeans, dry beans, small grains or alfalfa and avoiding continuous corn can reduce pathogens.
Two categories of symptoms are associated with the disease—leaf blight, which is most common, and the wilt phase. Leaf blight appears as large gray to tan lesions. Dark green to black water-soaked spots, referred to as freckles, occur on the surface of the leaf within an infected area. Bacterial "ooze" may also appear shiny in the sunlight after drying.
The wilt phase, while rarer, is more common in the Panhandle and western Nebraska. But it was confirmed last June in several fields in York County. "That's the earliest we've seen the wilt stage that far east in Nebraska, Jackson-Ziems says.
The wilt phase usually occurs as a result of early-season wounding of seedling corn from hail, sandblasting or high winds. But she says the bacterium can also enter the plant through natural openings.
Goss's wilt is around to stay, but not always severe every year, Jackson-Ziems says. "If you had it before, you'll have it again."
Plant pathologists have found some additional alternate hosts for the disease. Green foxtail had been the only foxtail species identified as host for Goss's wilt bacteria, but Tamara Jackson-Ziems, UNL plant pathologist, says that recent greenhouse trials show that yellow foxtail, bristly foxtail and giant foxtail also are hosts and could provide a reservoir of bacterial inoculum. Other known hosts are eastern gama grass, barnyard grass, sudangrass, grain sorghum and volunteer corn.