Cereal leaf diseases should be preventable. You can see them coming, since they start at the bottom of the plant and advance upwards. And it’s the flag leaf at the top that needs the most protection, so it should be easy to head off anything at the pass, right?
Unfortunately, the reality is not so clear cut. Weather, the tenacity of inoculum on stubble, moisture conditions and crop health, going into head, all play a role in disease outbreak and severity. Getting a handle on cereal leaf disease starts with knowing what to watch for and when to watch for it.
1. Know what to look for
“The most common cereal diseases are the leaf spots,” says Faye Dokken-Bouchard, plant disease specialist with the Saskatchewan Ministry of Agriculture. “We do surveys every year where we collect flag leaves and heads from about 150 fields across Saskatchewan, and leaf spots are almost always found on flag leaves.”
Tan spot and septoria are the primary leaf spot diseases of wheat and durum, while net blotch and scald are the major issues to watch for in barley.
Leaf and stripe rust are the other main diseases to watch for. Dokken-Bouchard says rust levels were up last year.
2. Watch the weather
Weather has an enormous influence on disease levels. The warm, moist conditions that are good for the crop are also good for disease outbreak, so step up your scouting efforts when conditions are right.
Also, watch for disease updates from the U.S., says Dokken-Bouchard. Rust usually blows up from the south, but it doesn’t always get here in time to cause damage.
Stripe rust has been known to overwinter when there is sufficient snow cover, as it did during the winter of 2010-11, neatly hopping from winter to spring wheat as it emerged. This winter has been remarkable for its lack of snow, so this may not be a concern.
3. Scout early and often
Start scouting for disease shortly after emergence. If you see some leaf spotting, you may want to include a lower rate fungicide in your early weed control application.
Keep scouting as the crop matures and monitor the progression of disease up the plant. Get down into the crop and check below the canopy because what’s happening on top of the crop is not necessarily reflective of what’s going on underneath.
4. the right spray
The flag and penultimate leaves are critical to grain fill, so it’s important to keep them healthy. The right timing and appropriate fungicide are critical.
For example, says Dokken-Bouchard, stripe rust has a greater potential to attack yield than leaf spot, so if you have both problems, choose a fungicide accordingly. “Know what disease you’re targeting and which product is most suitable,” she says.
Application timing is different for leaf and head diseases such as fusarium head blight (FHB), which has the smallest application window during flowering. Leaf spots and rust have wider windows of application, and the goal is to keep the flag leaf as free of disease as possible because you can’t erase damage that occurs before spraying.
5. Water volume
Water is your friend when it comes to fungicide application. Don’t skimp on volume. It can mean fewer acres covered with one tank and more trips back to the yard, but the key to fungicide efficacy is good coverage, deep down in the canopy where disease often originates, and that can only be achieved with generous water volumes.
6. Year round effort
As with all pest problems, the healthier your crop, the better able it is to cope with the stresses imposed by disease and to respond well to fungicide application. In a way, disease management should be a year round effort that includes observing good rotations, stubble management, seed treatments, proper nutrition, beneficial seeding practices, early weed removal and regular scouting. The more you do throughout the season to maintain crop health, the greater your harvest yield potential. †