Management of foliar wheat diseases, Part 2

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.    

Recent freezing temperatures in Michigan caused some injury to wheat foliage. Injury is showing up as tip burn, and in low areas of fields as more extensive browning of leaves. The wheat should recover with little impact on yield. However, be watchful for diseases this spring, as the stress caused by freeze injury may cause wheat to be somewhat more susceptible to foliar diseases. Part two of this series covers leaf rust, stripe rust, and fungicides for managing foliar disease of wheat. As of mid-April 2007, leaf rust has been showing up in parts of Texas and southern Kansas. A fact sheet containing the foliar disease management information from part one and part two can be found at: http://fieldcrop.msu.edu/documents/wheat%20foliar20%disease-final.pdf

Leaf rust

Cause: Wheat leaf rust, Puccinia triticina (fungus). (view image)

Symptoms: Infections first appear on the lower leaves. Reddish-orange spore masses of the fungus break through the leaf surface leaving an orange powder that rubs off the leaf. As the crop develops and matures, leaf rust generally appears on upper leaves of plants and severity increases.

Disease cycle: The fungus can survive on wheat during a mild winter or when covered by deep snow, or be carried in on wind currents from more southern areas as the wheat crop develops in spring.

Conditions favoring the disease: Temperatures of 60-80ºF and conditions that promote leaf wetness in the canopy for extended periods of time, such as rain, ground fog and dew increase the severity of leaf rust.

Management: The primary means of controlling leaf rust is to use resistant varieties. Scout fields from around heading to flowering. Several foliar fungicides are labeled for control of rusts. Check the label for application timing if a fungicide is used. The threshold for fungicide applications is an average 5-10 pustules/ flag leaf (averaged over 30-50 leaves). Avoid spreading the disease on clothing or farm equipment. Clothing, boots and farm equipment contaminated with rust spores should be cleaned before entering healthy fields.

Stripe rust

Cause: Stripe rust, Puccinia striiformis. (fungus) (view image)

Symptoms: Stripe rust appears as long stripes of small yellowish orange pustules on the leaves. The pustules are masses of rust spores. It can be confused with leaf rust, but the stripe rust pustules are arranged in rows, or stripes, while the leaf rust pustules are scattered on the leaf. Wheat is the only host for stripe rust.

Disease cycle: Stripe rust usually arrives in the north on wind currents from more southern wheat growing areas. It survives down south on volunteer wheat until it can infect newly planted wheat in fall and winter.

Conditions favoring the disease: Stripe rust is favored by cool, humid weather. Disease development is most rapid between 50 and 60ºF. The disease is inhibited when night time temperatures reach 65ºF or temperatures for several days in a row reach the mid 80’s.

Management: The primary means of controlling both leaf rust and stripe rust is to use resistant varieties. Several foliar fungicides are labeled for control of rusts. Fungicides aren’t commonly used for stripe rust unless the disease occurs early in the season. Check the label for application timing if a fungicide is used. Avoid spreading the disease on clothing or farm equipment. Clothing or boots contaminated with rust spores should be cleaned before being worn to walk through healthy fields. Likewise, rust can spread from contaminated farm equipment. Clean contaminated equipment before using it in a field of healthy plants.

Growth stage limitations for applying certain fungicides

Flag leaf emergence
(Feekes GS 8)

Flag leaf collar visible
(Feekes GS 9)

Heading
(Feekes GS 10.5)

Beginning of flowering
(Feekes GS 10.5.1)

Stratego- trifloxystrobin+
propiconazole

Quilt- azoxystrobin + propiconazole

Quilt- azoxystrobin + propiconazole (wheat only)

Folicur- tebuconazole

 

Propimax-propiconazole

Tilt- propiconazole

 

 

 

Headline- pyraclostrobin

 

 

 

Quadris-azoxystrobin

 

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