Prepare to face off against Goss’s wilt
By DON McCABE
For many Nebraska corn producers, Goss’s bacterial wilt and blight was like a scary, low-budget movie last year, but the sequel for 2010 could be even worse.
This bacterial disease has spread like prairie fire from west to east across the state the past three to four years, cutting yield in its wake, particularly in western Nebraska.
At a glance
• An old enemy returns to Nebraska’s corn fields.
• Goss’s wilt and blight continues its eastward march.
• Planting resistant hybrids is the best management strategy.
“In 2009, a Scotts Bluff County producer reported a yield loss of 75% in 40% of a field,” says Tamra Jackson, University of Nebraska Extension plant pathologist. “In 2008, a pivot circle in Chase County with a hybrid resistant to Goss’s wilt planted on half of the circle yielded 65% more than the susceptible hybrid planted on the other half.”
Based on leaf samples sent to the UNL Plant and Pest Diagnostic Clinic, the disease was identified in fields in almost half of the state’s counties. Jackson believes it infected corn in even more counties where leaf samples were not taken. Goss’s wilt and blight, first found in Dawson County in 1969 and a serious yield robber in the 1970s, subsided for years before resurfacing with a vengeance in 2006 in southwest Nebraska, the Panhandle, and parts of Colorado and Wyoming. It continues spreading eastward, even into Iowa, Illinois and Indiana.
“We are concerned about it for 2010 because the bacteria causing the disease is more prevalent in crop residue, and the bacteria can overwinter there and in soil,” Jackson says. “This is western Nebraska’s most important corn disease, and it could become that way in eastern Nebraska. ”Jackson’s blunt forecast: “If you had it before, you’ll have it again.” Goss’s wilt is a bacterial disease, so fungicides are not effective against it.
The main management strategy is to plant resistant hybrids. According to Jackson, 65% of the companies marketing hybrids in Nebraska rate them for Goss’s wilt resistance.
You can suppress Goss’s wilt and blight with practices such as crop rotation and tillage, but neither will eliminate it. Rotation to soybeans, dry beans, small grains or alfalfa can help to reduce the pathogens in corn residue. “The longer the rotation out of corn, the better,” she says.
As the name implies, there are two major categories of symptoms: leaf, or foliar, blight and systemic wilt. Most common is leaf blight, which 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. A bacterial “ooze” may also appear shiny in the sunlight after drying.
Rarer is the wilt phase in which the pathogen spreads throughout the plant. This can happen early in the year on seedling corn following a hail storm or strong winds that blow sand — as it has in western Nebraska. Resulting plant wounds allow the bacteria to enter the plant and become systemic, usually killing the plants before they mature, according to Jackson. Even slight, invisible wounding can lead to infection.
Systemic infection can cause losses of up to 50% in severe cases in susceptible hybrids.
Diagnosis is important. “About anyone who is comfortable with the distinctive symptoms caused by Goss’s wilt — the freckles and ooze — can diagnose it,” Jackson says, “but for quick confirmation you should submit a leaf sample to the UNL Plant and Pest Diagnostic Clinic. Start scouting fields within a week or two following a wounding event such as hail, high winds or sand blasting, especially if you have a history of the disease in your area.”
For more information on the clinic, go to pdc.unl.edu, where you’ll find directions on submitting samples. You can also call 402-472-2559.
DISEASE IDENTIFICATION: Kevin Korus, University of Nebraska plant pathology graduate student, holds a corn leaf with the typical symptoms for the leaf blight stage of Goss’s wilt. Note the gray to tan lesion on the leaf and the dark green to black water-soaked freckles within the infected area. A bacterial ooze appears shiny in the sunlight after drying. Close-up photo offers a better view of the symptoms.
This article published in the April, 2010 edition of NEBRASKA FARMER.
All rights reserved. Copyright Farm Progress Cos. 2010.