By Mitchell Japp, MSc, PAg, Provincial Specialist, Cereal Crops and Barb Ziesman, PhD, PAg, Provincial Specialist, Plant Disease
Corn is becoming increasingly common throughout Saskatchewan. Producers are choosing it for its high yields and consistent returns, for use as a grain, silage or grazing crop. Some early adopters have already been growing corn for a decade or more.
In the 2016 census, we observed that corn is being grown in every region of Saskatchewan and is reported at over 120,000 acres.
We often hear about new crops that, when introduced, are free from insects and disease. In areas of Saskatchewan where corn acres are low, the impact of pests is low due to a refuge effect. However, corn can be affected by several insects and diseases.
One such disease is Goss’s wilt, which can be a devastating in corn. It is a bacterial disease that is most prevalent where corn is grown regularly. Since is it is caused by a bacteria and not a fungus, fungicides will not be effective.
The pathogen that causes Goss’s wilt overwinters on infected crop residue, leading to higher levels of disease severity in fields with high levels of corn residue. The pathogen is not known to be long-lived and research indicates that the pathogen population decreases significantly after 10 months. This makes crop rotation a strong management tool to reduce pathogen levels in the field and reduce the risk of disease development and corresponding yield loss. Green foxtail and barnyard grass are hosts of the Goss’s wilt pathogen, so controlling these weeds will help keep disease at low levels.
Some corn varieties have resistance to Goss’s wilt. This would only be a priority if Goss’s wilt has been identified in your area.
Identifying Goss’s wilt starts with field scouting. Water-soaked streaking will appear initially. Later, the leaf will have shiny exudate on it and the lesions will develop a long, greyish, wavy pattern following leaf veins. Dark specks, sometimes called freckles, will appear. The freckles and shiny exudate are distinct symptoms for Goss’s wilt.
Bacteria enter the leaf through mechanical damage. Mechanical damage can be caused by wind, heavy rain, hail and feeding. Plant stomata are another potential site for pathogen entry.
Goss’s wilt development is favoured by wet and humid weather. There wasn’t a lot of hot, humid weather in Saskatchewan in 2018. However, corn is popular under irrigation, where high humidity conditions can be created.
One of the first steps in managing Goss’s wilt is to identify it. Visual symptoms can be mistaken for other diseases. If you suspect Goss’s wilt, submit your sample to the Crop Protection Lab for confirmation.
Goss’s wilt has been confirmed in Alberta and Manitoba.
For more information, see the Manitoba Corn Growers Association website.