Soy rust spores reach Ont., Man.

Emphasizing that spores by themselves don’t mean a disease outbreak, the Ontario ag ministry reports soybean rust spores have been found in rainfall samples collected in early July from eastern Ontario through to southern Manitoba.

In a newsletter on crop pests released Friday, the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) said the spores were confirmed in samples collected in the week of July 1 to 8.

The provincial and federal government regularly take rainfall and air samples to check for the presence of Asian soybean rust using PCR-based molecular tests designed to detect DNA from spores deposited in traps.

Using these methods, the province said, soybean rust spores were found in Canada for the first time during the 2007 growing season, most noticeably in mid-July and again in mid-August. Both those events had corresponded to storm fronts, which suggested long-distance transport of the spores. The Ontario Soybean Rust Coalition reported just one infected soybean leaf.

However, unlike in late June 2007 when the first rust spore detection was in one location (St. Thomas, Ont.), the first detection this month in 2008 was over a “wide geographical distribution from Manitoba to eastern Ontario,” the province said.

Positive spore locations for the week of July 1-8 this year included Woodslee, Ridgetown, Forest and Ottawa in Ontario, as well as at Morden in south-central Manitoba, the province said. The U.S. Department of Agriculture’s Cereal Disease Laboratory at St. Paul, Minn., detected rust spores in Minnesota and New York state during the same time period, the province noted.

“We are currently analyzing the rainfall samples from the last few weeks but have no data to present at this time,” the province said.

No infections

The province emphasized that no soybean rust infected plants have been found in Ontario. What’s more, the province said, soybean rust development in the southern U.S. has been slow this year due to unfavourable conditions for the disease.

With a return to better soybean rust conditions in the area, as may have happened in the southern U.S. with the arrival of Hurricane Dolly, new infections may result. But either way, the province said, the spore load in Canada and the northern U.S. has been low and the viability of the spores is “likely extremely low.”

“Finding spores is very different to having diseased plants in the field,” the province said. “Spores need to be deposited on a soybean leaf, environmental conditions must be favourable for germination and infection and finally, favourable weather conditions need to continue for the disease to develop.”

This year’s rainfall sits in “stark contrast” to last year’s hot, dry conditions, the province said, and while conditions were better in early July this year, the pre-flower stage of the soybean crop would have been mostly unfavourable for soy rust infection.

“Therefore, at this time we do not recommend fungicide management for soybean rust but we will continue to monitor soybean sentinel plots and grower fields in the province,” the ministry said in its newsletter.

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