If you haven’t already been walking your canola fields, now is the time, particularly after the very wet fall, warm temperatures right up to snow cover, and the extensive period of snow cover that added up to what can be perfect conditions for blackleg. In winter canola, look for lesions on primarily the lower leaves and leaf material that died back during the winter. The center of the lesions will have tiny black specks (pycnidia). Residue from previous canola crops and cover crops containing Brassica species should also be observed. Collect suspicious leaves, stems, and/or residues, and drop off or mail to WSU, UI, or OSU.
Both documents include who to contact at WSU, OSU and UI for assistance.
Dr. Xianming Chen, USDA-ARS Research Plant Pathologist in Pullman, and Dr. Mike Flowers, Oregon State University Extension Cereal Specialist, released disease updates (Dr. Chen’s update and Dr. Flower’s update) during the past week.
Not surprisingly, stripe rust has continued to develop on winter wheat across the region and is relatively easy to find. Dr. Flowers reported finding stripe rust at variety testing locations near Dufur and Moro, OR, and in a commercial field near Moro. Dr. Chen reported finding actively sporulating stripe rust during the week of April 5 in over 80% of the approximately 70 fields checked in Adams, Benton, Columbia, Franklin, Garfield, Walla Walla, and Whitman Counties in WA, and Umatilla County in OR.
Stripe rust was most active near Walla Walla and Pendleton, where many fields have been sprayed with fungicide already. In other areas, rust ranged from 1 to 5% and is less severe than last year at this time due to lower temperatures. The Palouse in Whitman County is an exception, with stripe rust appearing about one month earlier than normal and similar to the severe epidemic years of 2011 and 2016.
Current weather forecasts continue to favor rust infection and spread, raising the potential for another severe stripe rust epidemic year. High-temperature adult-plant resistance (HTAP) has not kicked in yet and won’t become fully effective until nighttime/daytime temperatures are above 50°F/65°F. Going forward, it will be important to continue scouting all winter wheat fields and consider using a fungicide with herbicide application if the variety is moderately susceptible or susceptible (rating 4 or greater in the Seed Buyers Guide) or active stripe rust is found on 2-5% of the plants in a field regardless of variety rating. Continue to monitor sprayed fields throughout the spring, especially near the end of fungicide effectiveness (3 to 4 weeks, depending on the fungicide). For spring wheat, plant the most resistant variety available, preferably those rated 1 to 2.
Additional rust updates will be released as the growing season continues and conditions change. You can find additional information on stripe rust, including photos showing rust percentage, under Foliar Fungal Diseases in the Disease Resources section of the WSU Wheat and Small Grains website.
For questions or comments contact Tim Murray by email (firstname.lastname@example.org), by phone (509) 335-7515, or Twitter (@WSUWheatDoc). For additional information contact Dr. Chen at email@example.com or (509) 335-8086; or Mike Flowers at (541) 737-9940 or at Mike.Flowers@oregonstate.edu.
Furrows of bleached-looking leaves of winter wheat damaged by pink snow mold in a Prescott, Wash., field.
By Linda Weiford, WSU News
Damage caused by snow mold in some eastern Washington wheat fields has surprised a Washington State University plant expert who has studied the fungus for nearly four decades.
Melting snow is exposing patches of injured wheat in parts of the state where destruction by snow mold is rarely seen, said WSU plant pathologist Tim Murray. He recently met with 20 growers in the town of Prescott, Wash., to address their concerns about the mold’s impact on winter wheat.
“Growers in this area have never seen this mold until now,” he said. “Its presence may have surprised me, but it really surprised them.”
After examining a half-dozen fields in southcentral and southeastern Washington, Murray identified winter wheat damage ranging from nonthreatening lesions on leaves to underground crown decay that kills the crop.
“I was surprised to see how prevalent the damage was in some of the fields,” he said. “We’ll definitely be seeing some economic damage as a result.” He stressed that the extent can’t be tallied until soils are warm enough to reveal which plants could withstand the damage and which could not.
Pink Fungus Among Us
A cold-loving organism that thrives under long periods of snow cover, so-called pink snow mold attacks perennial plants and overwintering crops. It’s more commonly seen in the higher elevations of northcentral Washington where snow blankets the ground for 100 days or more.
But this winter’s pervasive snowy weather fueled the mold’s growth in lower elevations as well, said Murray, including Walla Walla, Whitman and Columbia counties. Caused by the fungus Microdochium nivale, the pink-tinged mold is showing up in fields of winter wheat and even lawns of grass, he said.
“Snow protects winter wheat and other dormant plants from cold temperatures, which is a good thing,” he explained. “But the snow cover becomes a problem when it stays on the ground for too long, which is just what happened.”
In areas where the fungal disease is evident, snow had covered the ground 60-70 days. Although longer than most years, “it’s still not long enough to cause the kind of damage I’ve been seeing. It typically takes at least 100 days,” said Murray.
Why, then, is the fungus among us? Abnormally warm temperatures in November kept the ground from freezing before the first hard snow arrived, creating a more hospitable environment for Microdochium nivale to grow, he explained. That, coupled with a longer-than-usual period of snow cover, gave it just what it needed to thrive.
“The fungus is out there. As we’ve seen, when the weather allows it to take advantage of the situation, it does,” he said.
Growers Advised to Wait
Murray has spent 40 years helping to develop high-quality wheat varieties that mount a defense reaction against snow mold and other diseases that plague the crop in cold climates. Microdochium nivale is one of three fungi that cause snow mold in Washington.
Murray is advising growers to let a few weeks of warmer weather pass in order to assess the full impact of damage in their fields. At that point, they can decide whether reseeding will be necessary.