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.

IMG_0913

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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