Goss’s wilt spreads across Nebraska, biggest corn disease
Goss’s wilt continues its spread unabated across Nebraska, with more than 60 counties in which the disease had been officially confirmed as of 2010. But Tamra Jackson, University of Nebraska-Lincoln plant pathologist, figures it pretty much exists statewide.
“It’s just not yet confirmed by plant pathologists or seed company representatives in most of the remaining counties,” Jackson says.
Since it reappeared in Nebraska in 2006 after a more than 40-year absence, the bacterial disease has now spread to at least a dozen states and one Canadian province, according to Jackson.
At a glance
• The return of Goss’s wilt remains a serious problem in Nebraska.
• It’s caused by bacteria, so fungicides won’t work.
• Be on the lookout this year for gray leaf spot, too.
“It’s the corn disease we are most worried about,” she says. “It definitely remains the biggest disease concern in Western Nebraska.” Management recommendations have not changed, she says.
First, fungicides won’t work since it’s caused by bacteria, but that hasn’t stopped some from treating Goss’s wilt with those products anyway.
“One producer called saying he had twice applied fungicides, and infection worsened,” she says. “He could have saved about $50 an acre by not applying fungicides.”
A crucial step
Hybrids with resistance to Goss’s wilt are a crucial step.
“More than 60% of the companies that market hybrids in Nebraska have resistance ratings for the disease. You’re taking a risk planting susceptible hybrids,” Jackson says.
Rotations and tillage can suppress Goss’s wilt, but not eliminate it. Rotating to soybeans, dry beans, small grains or alfalfa can help reduce the pathogens in corn residue. “The longer the rotation out of corn, the better,” she says.
Jackson says that foliar treatment products have not been found effective against Goss’s wilt.
Two categories of symptoms characterize the disease, with leaf blight most common. 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 the infected area. Bacterial “ooze” may also appear shiny in the sunlight after drying.
The wilt phase is rarer. That’s when the pathogen spreads throughout the plant, which can happen early in the year on seedling corn after a hailstorm or strong winds that blow sand. These wounds allow the bacteria to enter the plant and become systemic, usually killing the plants before they mature. Systemic infection can cause losses up to 50% in severe cases in susceptible hybrids.
In 2009, a Scotts Bluff County field had 75% yield loss over 40% of the field, and in the same county a year earlier, an entire quarter sustained 65% loss.
You first need to identify the disease. For quick confirmation, send in leaf samples to the University of Nebraska Plant and Pest Diagnostic Clinic. Go to pdc.unl.edu to learn how to submit samples, or call 402-472-2559.
A company called Agdia has developed a test strip, called an immunostrip, to diagnose Goss’s wilt. Check with your crop consultant, agronomist or seed dealer to see if they know of it.
Gray leaf spot
A bit of good news on the corn disease front last year was the lack of gray leaf spot infection, although that’s no indication the same will happen in 2011.
“In spite of all the rain early last year, humidity levels were somewhat low,” says Jackson. “This is a good lesson on the importance of humidity in leading to diseases. Wet leaves are not the same as humidity.”
Southern rust, a severe problem for Nebraska corn in 2006, began to appear too in late August 2010 in southeast and south-central parts of the state, but it was late enough to avoid a major impact on yield.
A Web-based monitoring program for Southern rust, like the one for soybean rust, will be available in 2011. “We will report to that website counties where samples showed Southern rust activity,” she says.
Go to www.ipmpipe.org.
Early-season stresses, such as heavy rains that led to standing water, shallow rooting and nitrogen deficiencies, led to stalk rot problems. So did higher temperatures and lack of rain midseason in some areas, says Jackson. However, she adds, a dry fall and timely harvest helped prevent lodging.