Wheat Disease Update – May 29, 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); firstname.lastname@example.org
Thanks to several spring rain and snow storms the entire eastern half of Colorado is now drought free (http://droughtmonitor.unl.edu)! However, with all that moisture comes several foliar pathogens of wheat that are not frequently observed in the state. I visited the CSU variety trial locations near Julesberg, Haxtun, Yuma, Akron and Orchard last week and I notice significant amounts of tan sport (Figure 1), and also found Stagonospora leaf blotch in some areas and the early symptoms of Stagonospora glume blotch (SLB & SGB) (Fig. 2). Stripe rust was also present in these locations, but the disease incidence (% of plants in a field infected) was relatively low. However, I did see my first stripe rust infections on the flag leaf (Fig. 3).
NOTE: To view regional drought conditions, click on map above. State maps can be accessed from regional maps. The data cutoff for Drought Monitor maps is each Tuesday …
Tan spot is caused by the fungus Pyrenophora tritici-repentis. This fungus generally survives in wheat residue, and the fruiting bodies produce spores that can infect wheat leaves. In the spring and early summer, spores are dispersed by wind, germinate and infect wheat at a wide range of temperatures. During prolonged wet periods (24 hours or greater), large numbers of spores form in the diseased areas, and spores may be blown onto other wheat leaves to form new infections. Early symptoms are observed when the fungus infects the leaf and produce small, oval to diamond-shaped spots that will be found sporadically on wheat leaves. These spots will enlarge and turn tan, often with a yellow border, and have a small dark brown spot resembling an “eyespot” near the center (Figure 1). The eyespot symptom is best observed when holding the leaf up to the sunlight. There are three foliar fungal pathogens of wheat that all cause similar symptoms on the wheat leaves. These include tan spot, Stagonospora leaf blotch, and Septoria tritici blotch. This bulletin and disease guide both provide a nice summary of these diseases.
Finally, there was also Wheat Streak Mosaic Virus symptoms at each of the five CSU sites I visited, with Haxtun having by far the most significant disease severity of any of these sites, with both WSMV and Barley Yellow Dwarf Virus symptoms present (Fig. 4 & 5). The Haxtun variety trial is one of the stops on the 2017 CSU Wheat Field Days tour. This will be a great opportunity for growers to see first hand the difference in how wheat varieties respond to significant virus pressure. I will be at the field days on June 9 & 12-14 and look forward to chatting with everyone about some of the many diseases present in Colorado this year.
Submitted to BARN Media by:
Dr. Wilma Trujillo