Keep an eye on Goss’s wilt spread
A new disease to keep in mind when selecting corn hybrids this year is Goss’s wilt. The bacterial leaf disease and blight was found in Minnesota, South Dakota and North Dakota cornfields this year. Fortunately, it caused minor damage and didn’t significantly reduce yields in most fields.
However, some infected fields in Minnesota over the past two years have had considerable yield loss, says Dean Malvick, University of Minnesota plant pathologist. Goss’s wilt is capable of reducing yields by as much as 60 bushels per acre in Minnesota, he says.
But overall, the risk posed by Goss’s wilt may be low. Therefore, it may not be a good idea in all situations to select for Goss’s wilt resistance, if it means giving up other important characteristics.
The pathogen that causes Goss’s wilt can overwinter in the Dakotas and Minnesota, says Connie Strunk, South Dakota State University Extension plant pathologist, Sioux Falls.
The pathogen survives on corn residues and in grassy weeds. Infection can occur the following year in corn that has been subjected to and wounded by hail, heavy rainfall, sand blasting or strong winds. In order for infection to occur, plant leaf injury is required. The residue-borne bacteria must be splashed onto the plant and enter the leaf wounds. Disease development is favored by high humidity, rain and warmer temperatures.
What it looks like
Two symptoms often associated with this bacterial disease are leaf blight and systemic wilt. Lesions may be gray to tan in color with wavy irregular margins that follow the leaf veins. The most obvious characteristics are the dark green to black water-soaked lesions, often called “freckles,” that appear on the infected area.
Another characteristic is the bacterial ooze that may be found on the leaf surface. Dry bacterial ooze may appear to shine and glisten in the sunlight. When the bacteria enter the plant’s vascular system, the water-conducting tissues can become blocked, which can cause a mushy or slimy stalk rot, wilting and even plant death.
What to do
Strunk and Malvick recommend the following management steps:
• Rotate to a nonhost crop such as soybeans, small grains, alfalfa or dry beans. Rotation will help reduce primary inoculum in the corn residues, but will not completely eliminate the bacteria. The disease can show up in corn not grown on last year’s corn residue.
• Use tolerant hybrids. Check with your seed dealer for Goss’s wilt ratings.
• Consider tilling infected fields where appropriate. Use any type of tillage that buries infested residues and encourages residue decomposition.
• Control grassy weeds that may serve as additional hosts for Goss’s wilt.
There are no effective in-season control measures in preventing the spread of Goss’s wilt, according to Strunk and Malvick. Foliar fungicides do not offer protection against bacterial diseases.
For more information, contact Strunk at firstname.lastname@example.org or 605-297-3112; or contact Malvick at email@example.com 612-625-5282.
NEW DISEASE: Tan to gray lesions on corn leaves are symptoms of Goss’s wilt.
This article published in the November, 2011 edition of DAKOTA FARMER.
All rights reserved. Copyright Farm Progress Cos. 2011.