The corn disease Goss’s Wilt is established in Manitoba and farmers will have to learn to manage it, says Wilt Billing, Pioneer Hi-Bred’s area agronomist for Manitoba.
“Once a field has the disease, it has the disease,” Billing told farmers during the Manitoba Special Crops Symposium Feb. 10 in Winnipeg. “It’s not going away.”
Yield losses from Goss’s Wilt vary from almost nothing with light infections to severe when the disease strikes earlier and becomes widespread. Because Goss’s Wilt is caused by a bacterium, rather than a fungus, fungicides will neither prevent nor cure the disease, Billing said.
Goss’s Wilt overwinters on corn stubble as well as several weeds, including barnyard grass and green foxtail, but the bacterium can survive on corn residue in the soil for 10 or more years.
It’s spread by wind and rain and enters the plant through abrasions – even microscopic ones – caused by hail or wind.
“The good news is producers have successfully managed this disease in Nebraska and Colorado for over 30 years,” Billing said. “We will be able to beat this disease in Manitoba by incorporating hybrids with better resistance and improving our management practices.”
One of those practices is getting rid of corn stubble.
“Tillage is very, very important,” he said. “The bacterium survives on the stubble so the more plant stubble you can remove the better off you’re going to be. You’re removing the host for the disease essentially.”
Tillage alone won’t eradicate Goss’s Wilt, but it can make the difference between a light infection and a severe one, Billing said.
Rotating to other crops helps too. Other cereals such as wheat, oats and barley are not susceptible to Goss’s Wilt, Billing said.
Usually corn growers will see a light infection one year, probably from the disease blowing into the edge of a field from a nearby-infected field. If conditions are right the infection can be a lot worse the following season, Billing said.
Farmers can protect their crops by planting hybrids that are resistant to Goss’s Wilt. Pioneer Hi-Bred has three resistant hybrids suitable for Manitoba and is checking two others that might be as well. Pioneer Hi-Bred will continue to develop new resistant hybrids, Billing said.
Goss’s Wilt was confirmed in two cornfields in the Roland area in 2009. There were suspected infections in 2008 but not confirmed. Last year Pioneer Hi-Bred surveyed 240 cornfields across the province and found Goss’s Wilt in 87 of them.
About half the infected fields had only a bushel or two an acre yield loss, Billing said.
“About 30 per cent of the fields had a mild infection rate where you’d probably lose five to 15 bushels (an acre),” he added. “Twenty per cent of the fields were severe and when I say severe you’re talking in excess of 30-bushel losses. Last year we felt one of the severe fields lost in excess of 50 bushels (an acre).
“Just be aware that this disease did show up in the majority of the corn-growing area this year.”
The many rains and high humidity last year probably compound the problem, Billing said.
“Justbeaware thatthisdisease didshowupin themajorityof thecorn-growing areathisyear.”
– WI LT BILLING
Goss’s Wilt can strike in two ways – a later-season foliar infection or an earlier systemic infection. The former could come from infected seed. No systemic infections have been seen in Manitoba yet, Billing said. A systemic infection would probably kill plants before they were waist high, he said.
Foliar infections show up after tasselling, usually higher in the crop, but rains can wash the disease down into the lower leaves.
Goss’s Wilt symptoms from foliar infections include large grey to light-yellow lesions with water-soaked margins. Bacterial exudates on diseased leaves dry up on the leaf surfaces and appear shiny in sunlight and appear as dark-coloured freckles.
Goss’s Wilt was first discovered in Nebraska and Colorado in 1969. For the first 10 years or so the disease was managed through tillage and crop rotation, but now farmers in those states rely on resistant varieties, Billing said.
Since then the disease has spread east, west, south and north, including North Dakota and Manitoba.
Several years of having corn stand all winter unharvested, as well as increases in minimum tillage, zero tillage and strip tillage probably contributed to the spread of the disease, Billing said.