Wheat Disease Update – April 12, 2021

Dr. Robyn Roberts
Field Crops Pathologist and Assistant Professor
Robyn.Roberts@colostate.edu; 970-491-8239

Welcome to a new season of the Wheat Disease Newsletters! My name is Robyn Roberts and I joined Colorado State University in August 2020 as the new field crops pathologist and assistant professor. I am excited to bring you the newsletters this season, and I am looking forward to meeting you all in the coming year. If you have pathology concerns, please don’t hesitate to reach out and/or send photos. The best way to reach me is by email: Robyn.Roberts@colostate.edu. You may also call my office at 970-491-8239, but it may take a few days for me to get back to you by phone. I am also on Twitter and will post disease updates there as well (@RobynRobertsPhD).

Disease Outlook for 2021
100% of the state of Colorado is currently affected by abnormally dry conditions. Because of this, we expect that fungal diseases (such as stripe rust, tan spot, and leaf blotch) will be less prevalent across the state. However, be sure to scout your fields because microclimates and localized weather events, including dew and rainfall, may vary across sites and can impact disease conditions in your fields.

In the northeast counties (Sedgewick, Yuma, Logan, Morgan, Weld), wheat appears to be about a week behind normal growth for this time of year. In Kit Carson county, wheat is actively growing and tillering.

Disease Observations
No disease observations have been made at this time. Drought seems to be site-specific across the state. No freeze damage has been observed, and insect activity appears low.

Disease Watch

Fungal Diseases- Stripe Rust, Leaf Rust, and Tan Spot
There are reports of stripe rust and leaf rust in the southern states (TX, OK), but there are currently no reports of stripe rust or leaf rust in Colorado. Leaf rust is not commonly observed in Colorado, but stripe rust can be concerning in disease-conducive years. Stripe rust disease is dependent upon cool, wet weather, and the dry conditions across Colorado will likely inhibit and/or limit rust diseases. We will continue to monitor for rusts, and if you think you see symptoms please feel free to send photos.
Tan spot can appear this time of year as well, but due to the dry weather it likely won’t cause major problems because the fungus is dependent on wet conditions.

Disease Management
Growers are strongly encouraged to regularly scout wheat fields for diseases. Particularly, scout for stripe rust and viruses in the coming weeks.

Pests and Weeds
Insect Pests
There is currently low insect activity, but this is also the time to scout for brown mites and armyworms as the ground is dry.
Information about brown mites can be found here:

Mites in Wheat – 5.578

Information about armyworms can be found here:

Armyworms – 5.503

Weeds- Kochia and Blue Mustard
Kochia and blue mustard are emerging or actively growing.
Information about Kochia and its management may be found here: https://extension.colostate.edu/topic-areas/natural-resources/identification-and-management-of-kochia-and-russian-thistle-6-314/
Information about blue mustard and its management may be found here:

2119 – Blue Mustard Control

Volunteer wheat
You may observe volunteer wheat emerging this spring, and you might wonder if this volunteer wheat is a major source of viral diseases. The short answer is that spring-emerged volunteer wheat is less risky as a viral reservoir than summer-emerged volunteer wheat. Decisions about terminating spring-emerged volunteer wheat should be balanced with other agronomic practices and concerns. You can find more information about the ‘green bridge’ and risks for viral diseases due to volunteer wheat here: https://eupdate.agronomy.ksu.edu/article_new/spring-emerged-volunteer-wheat-should-producers-worry-about-wheat-streak-mosaic-virus-and-the-green-bridge-436-4

Plant Diagnostic Clinic
Do you have a disease that you would like diagnosed? Contact the Plant Diagnostic Clinic for sample submission: https://plantclinic.agsci.colostate.edu/ or plantlab@colostate.edu.

Dr. Wilma Trujillo, Area Agronomist, Logan and Morgan Counties, CSU Extension
Ron Meyer, Area Agronomist, Kit Carson County, CSU Extension
Dr. Robyn Roberts, Field Crops Pathologist, CSU

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