Late Season Crown Rust & Stem Rust in Oats

On a recent tour of the MCVET Portage la Prairie site,  I found both stem and crown rust present. Here is a quick refresher on the differences between stem rust and crown rust in oats.

Stem rust
Stem rust is caused by the fungus Puccinia graminis f.sp. avenae.  Symptoms include dusty, raised reddish-brown, oblong spots on the stems (see Figure 1), but can appears on leaves (see Figure 2). When developed, spots will rupture through the surface, releasing spores into the air. The surface of the tissue appears ragged and torn.

Stem Rust in 2016 MCVET Oat Trial - Portage

Figure 1: Stem Rust in Oats at MCVET Portage la Prairie Site (Photo by: P. de Rocquigny, 2016)

 

Stem Rust Symptoms on Leaves of Oats at Portage la Prairie MCVET Site (Photo by P. de Rocquigny, 2016)

Stem Rust Symptoms on Leaves of Oats at Portage la Prairie MCVET Site (Photo by P. de Rocquigny, 2016)

Crown rust
Crown rust is caused by the fungus Puccinia coronata f.sp avenae. The characteristic symptom is the development of small, scattered, oval-to-oblong, bright orange-yellow pustules (uredinia) on the upper and lower surfaces of leaves (see Figure 3). The powdery spore masses in the pustules are readily dislodged.  The number and size of the crown rust uredia vary greatly, depending on the susceptibility of the oat variety and the severity of infection. Crown rust is distinguished from stem rust of oats by the bright, orange-yellow color, the smaller size of the pustules, plus the lack of conspicuous, jagged fragments of oat epidermis adhering to the sides and ends of the pustules.

Crown Rust in 2016 MCVET Oat Portage

Figure 3: Crown Rust in Oats at MCVET Portage la Prairie Site (Photo by P. de Rocquigny, 2016)

As the oat plants begin to ripen, the black overwintering spores (teliospores) are formed (Figure 4). These spores also may form earlier in the season during periods of adverse weather, such as extreme drought, excessive moisture, or very high temperatures.

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Figure 4: Crown Rust in Oats at MCVET Portage la Prairie Site (Photo by P. de Rocquigny, 2016)

There isn’t much to be done at this stage of the growing season if either rust is found.  However, in future growing seasons control options would include planting resistant varieties, seeding early if possible, and application of fungicides.

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture

Source: Crown Rust of Oats: http://ipm.illinois.edu/diseases/series100/rpd109/
Rust Diseases in Canada: http://prairiesoilsandcrops.ca/articles/volume-4-10-screen.pdf

For additional information, visit Manitoba Agriculture’s website:

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Scout Your Oat Fields for Crown Rust

During the growing season, reports on the current rust situation and how it is progressing in the United States are available in the Cereal Rust Bulletins from the USDA at: http://www.ars.usda.gov/Main/docs.htm?docid=9757. Recently, crown rust has been reported in South Dakota and Minnesota.  These reports provide growers in Manitoba the opportunity to proactively scout for crown rust in their oat fields.

As a reminder, there have been changes within the crown rust pathogen populations in Manitoba where virulence has developed on a number of oat varieties. Varieties that contain the Pc91 gene, including AAC Justice, CDC Morrison, HiFi, Souris and Stainless, had been redefined for crown rust resistance in Seed Manitoba 2016 (www.seedmb.ca). The variety Summit, which is postulated to carry different resistance genes, is also losing its resistance to virulent races in the Eastern Prairies; therefore, it had also been redefined for crown rust resistance.

There are a number of steps used to determined if changes are occurring within the crown rust pathogen populations, and then whether changes in variety disease resistance ratings are required. Please take the time to read the attached article to learn more about how and why the crown rust resistance ratings did change in Seed Manitoba 2016.

Changes in Crown Rust Pathogen Populations Changes in Disease Resistance Ratings for Oats

Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture

With information from Dr. Jim Menzies, Phytopathologist, AAFC Morden & Dr. Jennifer Mitchell-Fetch, Oat Breeder, AAFC Brandon

 

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Stem Rust & Crown Rust in Oats

An agronomist contacted me in regards to finding rust in an oat field in Southern Manitoba. I toured out there today to find both stem and crown rust present in the field.  I also toured a MCVET oat trial where I could find stem rust in each of the entries.  I have provided a review below of stem rest and crown rust in oats.

Stem rust
Stem rust is caused by the fungus Puccinia graminis f.sp. avenae.  The disease appears as elongated reddish-brown pustules mainly on stems but also on leaves and heads. The powdery spore masses in the pustules can dislodge readily.

Stem rust causes yield losses through absorbing of nutrients that would otherwise be used for grain development, interferes with plant vascular tissue which can lead to shriveled grain, and it can weaken the stem causing lodging.

Stem Rust

Stem Rust in Oats. Photo by: Pam de Rocquigny, 2014

Crown rust
Crown rust is caused by the fungus Puccinia coronate f.sp avenae. The characteristic symptom is the development of round to oblong, orange to yellow pustules, primarily on leaves but also on stems and heads. The powdery spore masses in the pustules are readily dislodged. The pustule areas turn black with age.

Losses result from damage to leaves (particularly the flag leaf), which leads to reduced photosynthesis and transport of carbohydrates to the developing grain. This causes shriveled grain and reduced grain quality.

Crown Rust

Crown Rust in Oats. Photo by: Pam de Rocquigny, 2014

There isn’t much to be done at this stage of the growing season if rust is found.  However, in future growing seasons control options would include planting resistant varieties, seeding early if possible, and application of fungicides.

Submitted by:  Pam de Rocquigny, MAFRD Cereal Crops Specialist

For additional information, visit MAFRD’s website:

 

 

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