A corn disease that gained a foothold in Manitoba a few years ago is one to watch, according to a provincial crops specialist.
Veronica Owusu, crop production extension specialist with Manitoba Agriculture out of Gimli, says agronomists and farmers should check for Goss’s wilt. The bacterial disease has moved north from the American Midwest and found a hunting ground in corn fields throughout the south-central region of the province.
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“This disease was identified in Manitoba near the Roland area in a silage corn field,” she said. “It was first identified in the U.S. in Dakota, Iowa and Minnesota but it gradually came to Manitoba in 2009.”
Goss’s wilt comes in two forms. It may appear as a leaf blight with streaks of necrotic tissue along the lengths of the leaves and peppered with dark spots, almost like freckles.
There is also a tell-tale ooze that, once dry, forms a shiny surface. It can follow the vascular tissue into the stem, where it becomes systemic. A cross-sectional cut through the stem shows discoloured vascular tissue along with that slimy ooze.
“In the field, it can be confused with a biotic stress like heat and water because the wilting will be obvious,” Owusu said. “When it affects the leaves at the three-four stage, it reduces the photosynthetic ability of the plant and reduces the yield. It can affect the corn all season but usually it appears in late August and early September.”
Although it looks and sounds like a fungal infection, it’s not. Goss’s wilt is actually an infection of the bacterial pathogen Clavibacter michiganensis nebraskensis. It overwinters in corn stubble and stays active for 10 to 12 months. It may also grow on sorghum and some foxtail weeds.
“And since it’s a bacterial disease, it needs a wound on the plant so it can enter and create an infection,” Owusu said. “So when there’s a heavy rainstorm or hail damage to the plant, the inoculum spreads from the previous corn stubble.”
Rain splash transports bacteria from the stubble to the plant and deposits it on the leaf. If the leaf has sustained any abrasion, such as sand blasting by wind-blown soil or from hail damage, rain-transported bacteria can infect the plant.
“It can enter the plant and then start to show the symptoms … on the leaves,” Owusu said. “When it infects the plant, it can cause a yield loss of 20 to 50 per cent.”
Since it showed up in Roland, it has been found in several places in south-central Manitoba. In 2016, Manitoba Agriculture, in partnership with the Manitoba Corn Growers Association and the University of Manitoba, surveyed 142 corn fields south of Lake Winnipeg through the central region.
They found Goss’s wilt in 59 of those fields. Follow-up surveys found a few more, one in Portage la Prairie, two in the RM of Oakland and one in the RM of North Cypress-Lanford. It’s here and farmers have to manage it.
“Because it is a bacteria, no fungicide has proven effective for control. The only management practice has been crop rotation, not planting corn-on-corn,” said Owusu. “So you can rotate your crops with soy bean, wheat, oats or barley.”
As a bacterial disease, there is one advantage to a corn grower. It’s not particularly long lived in the soil. It only lasts for a year so, so rotating with an unsusceptible crop is not difficult. Tillage may also be an option but corn residue must be buried.
“And then there’s hybrid selection,” Owusu said. “Studies have shown that there are some good hybrids that (are) genetically resistant so, even though the disease might sometimes show, its impact will be less than that of a susceptible hybrid.”
Since this is a relatively new disease, there may not yet be resistance ratings in Seed Manitoba but they should be coming. Producers who are concerned may contact their local ag reps. Resistant hybrids have been developed in the U.S.
Farmers who think they’ve found infected corn in their fields can submit a sample to Manitoba Agriculture’s diagnostic lab. For more information, contact a Go Office.
