Seed & Chemical
Is it too late to spray for stripe rust?
By Top Crop Manager
July 20, 2015 - Some areas of Alberta are reporting an increase in stripe rust. With cooler, wetter weather in the forecast, many are wondering if a fungicide is needed.
Mike Harding, plant pathologist at Alberta Agriculture, says there are a few points to consider when making spray decisions for rust at this time.
"Stripe rust can infect cereals this late in the season, including green tissue, leaves, stems and glumes. It can also reduce yields even this late in the season but the amount of yield loss decreases dramatically after flowering," he says.
Harding says the likelihood of economic benefit from a fungicide drops off sharply after flowering unless the stripe rust levels exceed 65 per cent severity (more than 65 per cent of the flag leaf area covered with rust pustules) and growers should consider a few other things.
"If you're wondering how late you can apply a fungicide, we recommend you check the manufacturers' labels for PHI (pre-harvest interval) restrictions. Some fungicides have a PHI of 30 to 45 days, so the window for application begins to close rapidly after flowering," he says.
Harding also suggests choosing varieties with good SR resistance will help avoid stripe rust in next year's crop. "You can avoid a "green bridge" for the pathogen by delaying winter wheat seeding until mid-to late-September and using winter wheat with the best available SR resistance," he says.