Corn acreage is on the rise across the Prairies, but this year, Goss’s wilt has hit some areas hard.
Goss’s wilt is a bacterial infection, relatively new to Western Canada. It was first confirmed in Manitoba in 2009, officially found in Alberta in 2013, and in west-central Saskatchewan in 2018.
Sherri Roberts, a crops extension specialist with Saskatchewan’s Ministry of Agriculture, found Goss’s wilt in many corn crops in southeast Saskatchewan in 2019. This summer, she saw three fields south of Weyburn, Sask., that were completely devastated by Goss’s wilt. These were grain corn fields, she said, “and the cobs didn’t form. The leaves went brown, and there was no way for the plants to get chlorophyll to the ears.”
Goss’s wilt is residue-borne, meaning that it overwinters in crop residue and can be spread from field to field by wind. Having Clavibacter michiganensis subsp. Nebraskensis, the bacteria that causes Goss’s wilt, in your field does not necessarily mean your crops will be damaged. “It has to have some type of an entry point in order to get into the plant,” Roberts says. If a corn plant is injured by hail or an exceptionally strong wind, the bacteria can enter the plant when rain or irrigation water splashes bacteria onto the wound.
Did this year’s wet August and September make Goss’s wilt infections worse? “No,” Roberts says. Either the bacteria are present in the field and can enter the plants, or not. Once infection occurs, environmental conditions influence how severe that infection will become, but moist weather does not guarantee a disease problems, in the way that a fungus like fusarium is more damaging in wet weather. However, in the case of Goss’s wilt, if wet weather brings hailstones, the bacterium might have more opportunities to infect crops.
Corn plants infected with Goss’s wilt will have long, tan lesions in the centre, along their leaf blades. There may be lesions that appear wet, and these lesions may have what look like black freckles. When you hold the leaves up to the light, the lesions may be translucent.
Because Goss’s wilt is spread by a bacteria and not a fungus, fungicide is not an option. Once you have Goss’s wilt in your field, all you can do is manage the disease for future years. Here are five (well, four) ways to manage Goss’s wilt.
1. Keep a strong rotation: If you have the bacteria that causes Goss’s wilt in your fields and you want to continue growing corn, limiting corn in your rotation is “the number one thing you can do,” Roberts says. Growing corn on the same field year after year gives the bacteria more opportunity to grow in the residue. Growing crops that are not hosts to this bacteria, like alfalfa, oats, wheat, soybeans, will lower the level of bacteria in your field by allowing time for the infected residue to decompose.
2. Choose a resistant variety: Many corn varieties are resistant to Goss’s wilt, or at least have reduced susceptibility. However, it may take some sleuthing to find out which varieties have these traits. “The information is not always in the usual varietal tables,” Roberts says. Ask your seed sales rep for options for your area.
3. Control weeds: While wheat crops are not hosts for the bacteria that causes Goss’s wilt, many grassy weeds are. “If you’re not controlling your weeds,” Roberts says, you may be giving the bacteria a way to survive when you’re not growing corn. “Green foxtail is the number one weed in the Saskatchewan weed survey,” Roberts says. This weed is also a host for the bacteria that causes Goss’s wilt. “That may be why we’re seeing more Goss’s wilt in Saskatchewan,” Roberts says.
4: Watch for residue: Because this disease is primarily residue borne, it can be spread by equipment carrying residue out of the field. “If you’re in a contaminated field and you move to a non-contaminated field,” Roberts says, “you really want to do your bio-security practices.”
5. Don’t get hail: The damage caused by even a small hailstone can give bacteria an opening to infect a corn plant. This year, “there were several small, local hail storms,” in southeast Saskatchewan, Roberts says.
Where the plants are more advanced, the disease can do less damage. But even small hailstones can do enough damage to allow Goss’s wilt a way into your corn crop. “All it needs is a tiny ding.”