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Soybean Rust Spores Found in Ontario

A great deal of effort has gone into monitoring the spread of soybean rust in North America. In addition to the North American Soybean Rust Sentinel Plot Network where soybean fields and sentinel plots are monitored for the disease, new technologies such as the molecular detection and tracking of soybean rust spores continue to be added in our fight against this very destructive disease.

Over the past two years, spore trapping equipment was placed throughout the province to enable the screening of rainfall (filtrate) and air samples for the presence of Asian soybean rust using PCR-based molecular tests designed to detect DNA extracted from spores deposited in the traps. Samples are collected weekly by Ontario Ministry of Agriculture, Rood and Rural Affairs (OMAFRA) or Agriculture and Agri-Food Canada (AAFC) staff and sent to Dr. Sarah Hambleton at AAFC in Ottawa for processing.

Spore trapping results when combined with sentinel plots, computer prediction models and other information can assist in soybean rust scouting activities, management and ultimately reducing producer risk to the disease.

This early detection system is modeled on the one implemented by the USDA-ARS Cereal Disease Laboratory in St. Paul, Minnesota (much larger in scope) and established in the US since 2005.

Figure 1. JB Rain Collector

The establishment of this spore trapping network in Ontario allowed us for the first time to detect soybean rust spores in Canada during the 2007 growing season. Last year, the most noticeable events occurred in mid-July and again in the middle of August. Both of these events corresponded to storm fronts which suggest long distance transport of the spores.

As mentioned earlier this spore trapping network continues in 2008 and most recently soybean rust spores were confirmed in rainfall samples collected during the week of July 1st to 8th, 2008. Unlike 2007 when the first rust spore detection was found in one location (week of June 28, 2007 in St, Thomas, Ontario), this first detection in 2008 had a wide geographical distribution from Manitoba to Eastern Ontario. Positive spore locations for the week of July 1 through to the 8th, 2008 included: Morden (Manitoba), Woodslee (Ontario), Ridgetown (Ontario), Forest (Ontario) and Ottawa (Ontario). We are currently analyzing the rainfall samples from the last few weeks but have no data to present at this time.

Figure 2. Automated rainfall collector "LODA"

These Canadian observations support the 2008 observations by Charles Barnes and Les Szabo for the northern US soybean areas (the USDA-ARS Cereal Disease Laboratory in St. Paul, Minnesota) in which they detected rust spores in Minnesota and New York State during the same time period.

What does this mean?

Although these are significant findings we need to keep this in perspective. Please consider the following:

1. No soybean rust infected plants have been found in Ontario and we are continuing to scout the Ontario sentinel plots and grower fields.
2. Soybean rust development in the southern US has been slow due to unfavourable environmental conditions but with a return to better soybean rust conditions in the area ("Hurricane Dolly") this may result in new infections. Either way the spore load in Canada and the Northern US states has been low and the viability of the spores is likely extremely low. During transport, spores encounter very harsh conditions such as ultraviolet light, high or low temperatures, etc. which decreases survivability and therefore, reduces the likelihood of successful infection. For these reasons it often takes a large number of deposited spores to begin disease development.
3. Spores do not make a disease. Therefore, finding spores is very different to having diseased plants in the field. Spores need to be deposited on a soybean leaf, environmental conditions must be favourable for germination and infection and finally, favorable weather conditions need to continue for the disease to develop. The frequent rains this year are in stark contrast to last year when the conditions in Ontario were hot and dry. Although conditions were better in early July this year the soybean crop stage would have been mostly unfavourable for infection (pre-flower). 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.

Figure 3. Burkhard air sampler

Funding for many of the Ontario soybean rust projects was provided in part through the Canada-Ontario Research and Development (CORD) Program which is administered by the Agricultural Adaptation Council as well as the AAFC Pest Management Centre, the Ontario Soybean Growers, Manitoba Pusle Growers and the Ontario Soybean Rust Coalition (through AAFC CanAdvance Program).