“Do not panic but rather get out there and scout your field. Early detection is critical. Yield losses can be significant.”
– NSAC REPORT
BA S F ’s fungicide Headline (pyraclostrobin) has received an emergency-use registration to control sunflower rust, a disease that decimated some fields in Manitoba last year and could be a problem this year.
“The rust that we’ve been finding (this year) is widespread around the province and it came in early so that’s a concern too,” Darcelle Mabon, executive director of the National Sunflower Association of Canada (NSAC) said in an interview last week.
“It’s a preventive product, so you have to get in early. As long as guys stage their timing right they shouldn’t have any problems with rust through until harvest.”
Application timing is important for season-long control, said Anastasia Kubinec, Manitoba Agriculture, Food and Rural Initiatives’ business development specialist for oilseeds.
Headline will protect a sunflower crop from rust for about 14 days. The fungicide can only be applied twice. It’s important to protect the top four to six leaves when the seed is being pollinated and filling so it’s important not to spray too early.
“You don’t want any stress on that seed formation otherwise you’re going to have reduced yields and reduced test weights as well,” Kubinec said.
“If guys are seeing a lot of that brown rust on their plants, they could have a full-blown infection by the time they get to that R 5.1 stage so they may want to pull the trigger earlier.”
Rob Hornford, BASF’s senior technical development representative for oilseeds and pulse crops, said farmers growing rust-tolerant varieties might be able to delay spraying longer than those growing susceptible ones.
Headline is the only fungicide currently available to control sunflower rust, so Kubinec wants farmers to use it wisely. Overuse could result in rust becoming tolerant to the fungicide, which is used on a number of crops to control a wide range of fungal diseases.
The NSAC is monitoring fields for rust and posting its findings at www.canadasunflower.com.In its July 13 report the NSAC says the “economical stage” of sunflower rust (brown pustules) has been found in one field in western Manitoba.
“Do not panic but rather get out there and scout your field,” the report says. “Early detection is critical. Yield losses can be significant.”
Rust has been found at various levels of infection in 100, 55 and 45 per cent of fields surveyed in the western, south-central and north-central regions.
In 2008, 74 per cent of Manitoba sunflower fields were infected with sunflower rust, with leaf damage averaging 15 per cent, MAFRI said in its submission for emergency-use registration to the Pest Management Regulatory Agency earlier this month.
Kubinec estimated the rust cut yields an average of 25 per cent with yield loss up to 75 per cent in individual fields. Low kernel density also resulted in downgraded confectionery sunflower seeds.
A 25 per cent yield loss conservatively cost Manitoba farmers $13. 65 million, according to MAFRI.
The last severe sunflower rust outbreak before last year occurred in 2003.
“We had guys (last year) that didn’t harvest (sunflowers) at all simply because it came in too early and it stunted the plants and it was all the way to the top of the heads and no time to recover from it,” Mabon said.
Rust hot spots last year included southwest Manitoba and around St. Claude, she said.
Most of the sunflowers grown in Manitoba are rated “moderately susceptible to sunflower rust.
MAFRI said in a greenhouse study, only five of 71 commercial sunflower varieties were resistant to a mixture of sunflower rust races. No confection sunflower varieties were resistant. In Manitoba, 60 per cent of the sunflowers grown are confection type.
Sunflower rust overwinters in Manitoba and spores also blow in from the United States.
PMRA granted the emergency-use registration July 15 and it expires Dec. 31, said Jeanette Gaultier, MAFRI’s pesticides, minor use and regulatory specialist.
Meanwhile, BASF has submitted a request to the PMRA to add sunflower rust to its label permanently. [email protected]