Know Your Enemy: The Key to Fighting Cereal Leaf Diseases

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Jordan Peterson Manager of Agronomic Services in Northern Alberta, Nutrien Ag Solutions

More articles by Jordan Peterson

Knowing how to identify cereal leaf diseases in your wheat and barley fields is a critical aspect of crop management. If it’s not done correctly and the right fungicides aren’t applied at the right time, crop losses could be as high as 25 per cent under heavy disease pressure.

That is because diseases, such as tan spot, septoria and stripe rust in wheat and net form or spot blotch and scald in barley, can spread rapidly in your fields if conditions are right. A spell of hot, wet, humid weather could mean the difference between a successful crop and a disappointing harvest.

Depending on your crop rotation, you may not see any signs of disease much before your regular spray timing, but it doesn’t hurt to start looking right from the start. Cereal leaf diseases often overwinter on stubble and will move upwards on infected plants, so it’s possible to observe the presence of disease as early as your first emergence check.

Tan spot disease in wheat is indicated by tan to brown spots, which fade into a yellow ring along the edges of the lesion. Septoria will present as yellow to brown spots with black dots in the middle, and the rust diseases can be identified by their orange pustules.

In barley, light brown spots that form a net-like pattern on leaves indicate net form blotch, while scald forms pale lesions on leaves that are usually tan in colour with brown margins.

A lot of growers are very good at detecting disease in their crops, but they may need some assistance to zero in on exactly which one they’re looking at. Consulting an agronomist or crop consultant can be a big help.

Once a disease is identified, it’s important to monitor its development and keep a close eye on the kind of weather you can expect to see in the foreseeable future. Scouting weekly (even twice a week when it’s close to flag leaf timing) is a good idea, and you want to make sure you’re covering as much of the field as you can.

When it comes to disease control, protecting the flag leaf and penultimate leaf of your wheat or barley plants is the most important, because that’s where 60 to 80 per cent of the grain fill comes from.

For wheat, spraying foliar fungicides at the four- or five-leaf stage will help suppress some of the early-season disease, but it won’t do anything for leaves emerging after that. That’s why it’s essential to time your applications correctly so the top two leaves are thoroughly coated with a protective fungicide.

It’s particularly important to scout your fields thoroughly for leaf diseases when wheat plants are at the five-leaf stage. Once your crop hits the flag-leaf stage and you know there’s disease present, try to time your fungicide application within a two-week window after the first flag leaves start to emerge.

Cereal leaf diseases can take a heavy toll on your wheat and barley crops — and your bottom line. Early detection, identifying the right disease, monitoring disease development and timely fungicide applications will all help to reduce the effects of disease on your crops and provide them with the best chance of success.