“If you get behind rust, you can’t manage it. If you get a fungicide on about R5, you’re going to protect your yield. It’s all about the timing.”
Before seed goes in the ground, producers should also think about sunflower rust, a disease caused by the fungal pathogen Puccinia helianthi.
When sunflower rust shows up at the bloom stage (R-5) or earlier, especially on confection hybrids, and there is more than one or two percent covering the upper leaves, yield loss will occur unless the disease is managed, says Dr. Samuel Markell, Professor and Extension Plant Pathologist of North Dakota State University.
“Rust can really knock your yield if it starts early and you have lots of days with wet leaves, but it’s also one of the easiest diseases to manage,” he says.
Some sunflower hybrids are resistant to rust, and fungicides also work well on the disease. Usually, rust is carried by wind into a field from other fields or residue. Growers often start to see infection symptoms during the late vegetative stages. “Rust, in general, is a dusty cinnamon brown pustule, and if you rub it off you tend to have a little white clearing underneath,” says Markell.
Scouting for rust is essential as the crop approaches the bloom stage. One percent severity on the upper four leaves at or before bloom is the action threshold for fungicide application.
“That’s about the time a grower might put an insecticide application down for protection from some of the head insects. Right before that point, I would encourage growers to scout. And if they see rust on the upper leaves – anything more than a trace amount, because one percent isn’t a lot – they might want to think about putting a fungicide on as well,” he says.
“If you get behind rust, you can’t manage it. If you get a fungicide on about R5, you’re going to protect your yield. It’s all about the timing.” After the bloom stage is over, at R-6 or R-7, rust won’t affect yield. “All it does is help dry down the crop,” says Markell.
Both the strobilurin (Headline®) and triazole (Folicur®) fungicide classes work well on rust, he adds.
The sunflower rust pathogen can withstand winters in the United States and Canada. Wild sunflower populations as well as volunteers can harbor the rust pathogen. Markell recommends producers get rid of these plants if they are adjacent to their fields.
For a limited time, email firstname.lastname@example.org to request a copy of the NDSU Sunflower Disease Diagnostic Series cards.