04-27-17 CSU Ext ALERT: Wheat Disease Update – Kirk Broders, Plant Pathologist…

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Allmer Wheat Fields Sec 34 053116

Photo courtesy of The BARN – May 31, 2016

Wheat Disease Update – April 27, 2017

Written by: Kirk Broders, Plant Pathologist; Department of Bioagricultural Sciences and Pest Management, Colorado State University; C030 Plant Science Bldg., 1177 Campus Delivery, Fort Collins, CO, 80523-1177; 970-491-0850 (work);  kirk.broders@colostate.edu 

The wheat crop in Colorado is on average between Feekes growth stage 6-8 (jointing to second node). Much of the state has received some moisture and so the crop continues to look good, but additional moisture in some areas will be needed. The limited moisture has had a positive effect in that very few foliar fungal diseases have been reported to date in Colorado. However, stripe rust continues to be reported in additional counties in central Kansas (See report from Erick Dewolf below). With cool wet weather predicted for next week, it is possible that Colorado will begin to see the first signs of stripe rust in the eastern most counties. If stripe rust arrives, and there is a need for fungicide applications, I recommend growers wait until the flag leaf is fully or nearly fully emerged. This is a critical growth stage and important to protect the flag leaf from infection. This will only be necessary if stripe rust posses a threat to yield. I will continue to keep you updated on the progress of stripe rust and whether fungicide application will be necessary.

The diseases I observed most frequently throughout the eastern Colorado, were viral diseases. So far we have identified Wheat Streak Mosaic Virus (WSMV), Triticum mosaic (TriMV), High Plains virus (HPV) and Barley Yellow Dwarf Virus (BYDV) in several fields. Of the 15 fields surveyed to date, 11 were positive WSMV, 7 were positive for TriMV, 5 were positive for HPV and 4 were positive for BYDV. While WSMV is the most frequently observed viral pathogen, 11 of the 15 fields tested had at lease 2 viruses present (Figure 1 & 2). This included fields from Adams, Arapahoe, Lincoln, Washington, Kit Carson, Yuma, Logan and Morgan counties. As the wheat continues to mature the expression of virus symptoms continues to become more evident. Many of these viral infections likely occurred last fall after the wheat germinated, and then we continued to have very mild temperatures until late November. However, I believe we are seeing the first signs of secondary infection, where wheat curl mites are becoming active and moving to previously healthy fields and infecting wheat plants in these fields with virus pathogens. Once wheat is infected with any of these viruses there is no chemical treatment that can eliminate the pathogen. In fields where virus diseases are present it will be important to ensure volunteer wheat and weeds are managed, as these represent “green bridges” for the wheat curl mite, which vectors WSMV, TriMV and HPV, to survive from one wheat crop to the next. If you believe you are observing virus symptoms in any of your fields, but are unsure of the diagnosis, or would like to know which viruses are present, I would encourage you to send samples to the CSU Plant Disease Diagnostic Clinic.

Figure 1. Symptoms of wheat infected with WSMV and HPV

Figure 2. Symptoms of wheat infected with WSMV and TriMV

Report from Dr. Erick Dewolf, Extension Plant Pathologist, Kansas State University. This week has brought more reports of stripe rust in Kansas.  Stripe rust can be found in the lower and middle canopy of many fields in central Kansas, but the severity remains low. Stripe rust is more severe in the southeast region of the state and has moved to the upper leaves in some fields. The weather conditions this past 14 days have not favored the rapid spread of stripe rust. Stripe rust is favored by cool, wet weather and temperatures in recent weeks were too warm for the stripe rust fungus to function efficiently. For example, most areas of the state had more than 30 hours of temperatures above 75 F in the last two weeks.  Some areas of southwest and south central Kansas had more than 50 hours of unfavorable temperatures. There were multiple nights with temps in the mid. 60’s in most of these areas. The threat of stripe rust has not past, however.   The disease could increase rapidly if we get into another period of favorable weather with frequent rainfall and temperatures in the 40-50F at night. I still think there is a moderate risk of Kansas having a serious problem with stripe rust this season.

Leaf rust was reported previously in south central and southeastern Kansas.  This week, brought a few new reports of leaf rust and indications that leaf rust has moved to the upper leaves in few areas.  This movement of rust to the upper leaves is important because these leaves provide most of the resources the plants will use produce grain. Any damage done to the upper leaves increases the risk of yield loss.

Maps showing the current distribution of stripe rust and leaf rust in the state are below:

Kirk  D. Broders, PhD
Assistant Professor
Department of Bioagricultural Sciences and Pest Management
Colorado State University

Office: 970-491-0850

Submitted to BARN Media by:

Dr. Wilma Trujillo

Area Agronomist
Logan and Morgan Counties
Colorado State University Extension
Cell: (719) 688 – 9168