June 30, 2022 | Eastern Canada
There has been a lot of talk regarding Tar Spot in the past couple of years , and with good reason. This disease migrated from south of the border and moved into Southern Ontario by winds. Tar Spot (depending on time of infection) can rob a corn crop of up to 60% of potential yield. This disease not only continues to blow in from the US, but it can also overwinter on stover and in soil.
The greatest potential for infection comes from overwintering spores. If you have detected infection in 2021, there is risk to not only neighbouring fields, but it will also infect volunteer corn in the following soybean/edible bean crop. Early control of said volunteer corn is essential to reduce soil spore load. In a corn-on-corn scenario, which has the greatest risk, scouting is key to suppressing and managing Tar Spot. The use of in-crop fungicides is a must to reduce yield impact.
Tar Spot can be identified by black raised lesions on the plant that cannot be smeared or wiped off like rust or insect frass, and transfer to the other side of the leaf. While the plant is infected, tissue decay is rapid and typical infection coincides with tassel timing at the reproductive stage and as the plant tries to produce a cob. Plant deterioration is accelerated when the lack of chlorophyl production is stalled at the same time the plant is pulling nutrients from reserves to ensure grain fill. Thus, leaving stalk integrity as well as kernel depth/weight subpar at best.
With the collaboration of industry on both sides of the border, there has been a mobile app created to track weather patterns, rainfall, humidity, and temperature that will inevitably predict whether Tar Spot will be a concern, and when to scout for it. This can be found by searching in the app store for “Tarspotter”. This is a user-friendly app that can help mitigate production losses.
If you have questions regarding this “new” disease and if Tar Spot is a concern in your area, please contact your local P&H agronomist to discuss, and for information on fungicides best suited for controlling Tar Spot.