Wednesday, May 18, 2011

Cool, Wet Weather Gives Rise to Stripe Rust

From Nyssa, OR, to Parma, Idaho, to Cassia County, Aberdeen, Bingham County, Idaho, American Falls, Power County, Idaho.

Expanding reports of stripe rust continue in commercial wheat fields. Affected fields include the varieties ‘Brundage’ soft white winter wheat, and ‘Malcolm’, soft white winter wheat, Stephens (SWW), and lower levels are being reported in Moreland (HRW), WB 528 (SWW), WB 470 (SWW), but it is expected that other susceptible winter and spring varieties will also begin to show symptoms soon. Stripe rust has also been found in the Aberdeen area on the University of Idaho’s research farm. The infected plants were at the jointing growth stage. New leaves were not yet showing infection; the disease was occurring on lower leaves likely as a result of an infection that started last fall. Infected plants that were covered by an insulating layer of snow carried the fungus through the winter and is the current source of the disease.

On the Aberdeen research station, Brundage had about 30% affected leaves throughout the plot, while Moreland about 5% of the leaves affected. Active and abundant spores were seen on infected plants. Stripe rust was prevalent throughout the winter wheat variety trials.

Resistant varieties should not need fungicide applications. Growers should scout all wheat fields and should never assume that resistant varieties will always be resistant, as the prevalent strains of the fungi can change, affecting different varieties.

The weather has been very conducive for infection and rapid spread. It is imperative to protect susceptible varieties with a fungicide as yield losses to this disease can be significant. Both strobilurin (Quadris, Headline) and triazole (Caramba, Tilt, Proline, Folicur, Prosaro) fungicides are equally effective in protecting against subsequent stripe rust infections, as are mixed mode-of-action fungicides (TwinLine, Quilt, Quilt Excel, Stratego). However, if stripe rust is currently in your crop, it is recommended that you include a triazole fungicide for the slightly curative activity.

Fungicide ratings for stripe rust from the mid-west are: Excellent = azoxystrobin (Quadris), pyraclostrobin (Headline), metconazole (Caramba), tebuconazole (Folicur), and fungicide mixes rated Excellent for stripe rust includes prothioconazole and tebuconazole (both found in Prosaro), and the strobiluron / triazole mixes line, Twinline, Quilt or Quilt Xcel. Rated very good was propiconizole (Tilt), and the mix of propiconazole and trifloxystrobin (Stratego). In the 2011 Pacific Northwest Plant Disease Management Handbook, Bumper was additionally listed for an effective foliar fungicide.

This information is provided only as a guide. Other fungicides may also be labeled and effective against stripe rust. Inclusion in this list is not intended as a product endorsement and exclusion from this list is not meant to imply other products are ineffective.

Additional information and pictures are available on the Cereals Extension website for southern and southeast Idaho:

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