The Agronomists, Ep 122: Managing tar spot and gibberella with Dale Cowan and John Seliga


Sharing is caring, except for when it comes to crop diseases. Many of the diseases that impact corn have in fact been shared through spores in the wind at some point, but most have become endemic to the corn producing regions of Canada.

For this episode of The Agronomists, host Lyndsey Smith is joined by Dale Cowan of AGRIS Co-op, and John Seliga with Corteva, to discuss managing tar spot and gibberella. From hybrid selection, to aerial vs. ground spraying, and on to the role of understanding the disease, these two experts dig in on corn management.

This episode of The Agronomists is brought to you by ADAMA Canada, the Corn School, and RealAg Newsletters.


  • We started on time. Woo!
  • We will talk about a few different diseases but the focus tonight is on tar spot and gibb
  • But first, a soybean update: here’s root rot out there, but there’s a lot of white mould… across the board. Especially in horticulture rotations
  • Anthracnose south of the border in corn
  • Spider mites in corn does in fact occur
  • Tar spot is the new-ish disease, but we don’t want to ignore the other diseases we have to worry about
  • It’s important to take a look at your disease risk maps. Check out the episode for some of the top ones across North America, built by Corteva
  • The risk maps are meant to be an indicator to scout, not necessarily spray
  • Tar spot came here from the midwest on the spore load. Sharing is caring… but maybe not with diseases
  • You cannot minimize how quickly tar spot can progress…it happens so quick
  • Breeders are currently working very hard to develop hybrids that are resistant to tar spot. They really only started working on it it in 2021

CLIP 1: A look at spray timing on tar spot control

  • Does it pay to double spray?
  • If you are in high risk… is there an ideal window to spray? As of today, based on what we know and the experience we have had, that VT to R1 timing seems to be most effective at controlling the majority of the infection
  • With diseases, so much depends on what the environment is like at the time (and after) spraying
  • Gibberella ear rot… the problem that will never quite go away
  • Won’t the cool temperatures slow the development of the disease so that it takes longer to become an epidemic now?
  • This is about risk management
  • It’s a very frustrating diseases. It’s a very definitive type of conditions that cause it — so really, any hybrid is susceptible. Makes it very tough to control
  • A lot of hybrids left the market once the companies across the board looked at which ones had a higher susceptibility (from 2018)
  • Breeders have to screen a lot of material. They are then left with the biggest rockstars of the group
  • Every hybrid at some point or another comes to the end of its life
  • Can we say it enough? Environmental conditions are everything
  • Sometimes we get plants with a second ear — no it’s not going to make grain, but does it contribute to DON?
  • A later emerging plant has much higher DON level risk
  • You have to understand your groups of fungicide and what targets what
  • It’s not always A+B = C… there’s so many complicated factors. That’s why we can dedicate entire shows to this. It’s very hard to wrap our heads around.
  • DON by itself is tolerable. DON plus a whole cocktail of mycotoxins is when the real problems occur

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