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 (email@example.com), by phone (509) 335-7515, or Twitter (@WSUWheatDoc). For additional information contact Dr. Chen at firstname.lastname@example.org 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.
Dr. Chen, USDA-ARS Research Plant Pathologist in Pullman, and the Oregon State University Variety Testing and Plant Pathology Team (Mike Flowers, Larry Lutcher, Christina Hagerty and Chris Mundt) each released disease updates (Dr. Chen’s report and the Plant Pathology’s report) during the past week.
Using six different models based on air temperature, Dr. Chen is predicting this year’s stripe rust epidemic will be more severe than his first prediction in January. Although air temperature during several periods in December and January was below the 5°F threshold for survival of the stripe rust fungus in plants, most of the wheat-growing area in eastern Washington had a blanket of snow cover that protected both winter wheat plants and the fungus, allowing both to survive. Consequently, Dr. Chen is now predicting an epidemic with potential yield loss of 32% on highly susceptible varieties, compared to 6% in his January forecast. Dr. Chen also reported finding actively sporulating stripe rust pustules during the week of March 6 in Walla Walla County where the wheat has greened-up and started growing. Fields farther to the north in Adams and Lincoln Counties were either still under snow or, where snow was gone, had dead spots where rust infection was severe last fall, or fall-infected leaves were dead. It is possible that the stripe rust fungus is still alive in these plants and may begin to sporulate once the plants begin growing again. These observations were confirmed in the OSU report, and stripe rust was observed on several varieties at two variety testing locations (Lexington, OR and Walla Walla, WA) and appears to be widespread in eastern Oregon and southeastern Washington.
Going forward, it will be important to scout all winter wheat fields and consider using a fungicide with herbicide application if the variety is moderately susceptible or susceptible (rating of 5 to 9) or active stripe rust is found on 2-5% of the plants in a field. Continue to monitor fields throughout the spring, especially as the end of fungicide effectiveness nears (3 to 5 weeks, depending on the fungicide). For spring wheat, plant the most resistant variety available, preferably those rated 1 to 4.
Metalaxyl is the active ingredient in fungicides such as Ridomil, Apron, Subdue, and others used to prevent root rots and seedling diseases caused by the fungus-like organism Pythium. Called Oomycetes, these fungus-like organisms require water for a portion of their life cycle, because most produce a swimming spore and are more closely related to brown algae than to true fungi like stripe rust. Other common oomycetes are the downy mildew and the late blight pathogen on potato. Pythium is a soilborne pathogen present in most agricultural soils that is able to attack a diversity of crops grown in the PNW including wheat, chickpeas (Chen and Van Vleet, 2016), lentils, canola, potatoes (Porter, et. al, 2009), other vegetables, and even the tree fruit. Because Pythium is not a true fungus, only certain fungicides can be used to protect a crop with, metalaxyl being most frequently used, most often in the form of a seed treatment. Unfortunately, in both potato-producing regions and in chickpea production in the Palouse, metalaxyl-resistant Pythium have been found. These resistant Pythium species are able to cause damping-off, stand and crop loss, and leak (in potatoes) despite the seed treatments. The fungicide ethaboxam is proposed as an alternative for managing metalaxyl resistant Pythium populations. As metalaxyl is our main weapon against Pythium and other oomycetes, it is vital that we be aware of developing resistance so that we can manage these populations and slow further development. Changes in management practices that encourage the rapid growth of seedlings and reduces cool, wet soil conditions until plants are robust enough to withstand minor damage can also help reduce the impact of Pythium.
If you suspect that you may have metalaxyl resistant Pythium, you are encouraged to submit a soil or plant sample to the Plant Pest Diagnostic Clinic in Pullman for testing.
For more information:
Weidong Chen and Steve Van Vleet. Chickpea damping-of due to metalaxyl-resistant Pythium: an emerging disease in the Palouse. 2016. http://hdl.handle.net/2376/6273
Cook, R.J. and B.X. Zhang. 1985. Degrees of sensitivity to metalaxyl within the Pythium spp. pathogenic to wheat in the Pacific Northwest. Plant Disease 69: 686-688.
Porter, L.D., P.B. Hamm, N.L. David, S.L. Gieck, J.S. Miller, B. Gundersen, and D.A. Inglis. 2009. Metalaxyl-M-resistant Pythium species in potato production area of the Pacific Northwest of the U.S.A. American Journal of Potato Research 86: 315-326.
As soil acidification continues to be a concern for growers in the Pacific Northwest, WSU researchers are working to provide information and recommendations for how to mitigate adverse effects. Root diseases are one of many factors influenced by acid soils, depending on the soilborne pathogen. The new publication, Acid Soils: How Do They Interact with Root Diseases?, explains how soil pH affects root diseases and also offers examples of common ones in the Pacific Northwest.
Cereal growers in the Pacific Northwest have been experiencing an increase in soil acidity (lower pH) primarily due to a long history of ammonium fertilizer use.
In eastern Washington and northern Idaho, soil acidification tends to be worse in areas that are annually cropped, do not include nitrogen-fixing legumes in the crop rotation, and in areas that were historically forested. Forested soils tend to have a lower pH buffering capacity, making them more prone to shifts in soil pH. These same areas also typically include more forage and seed grass production and seldom include legumes in rotation, meaning that there is more intensive nitrogen application to the soil.
In addition, direct seeding can result in a stratification of soil pH in which the top few inches of soil are more acidic. This is because acidification caused by fertilizer application in the top soil layers is not diluted by mixing with the more alkaline soil below the fertilizer zone. However, the contribution of this stratification on management of soil acidity in direct-seed systems has not been evaluated.
For questions or comments, contact Tim Paulitz at USDA-ARS Wheat Health, Genetics and Quality Research Unit (email@example.com or firstname.lastname@example.org) or Kurtis Schroeder, Assistant Professor in the Department of Plant, Soil, and Entomological Sciences at the University of Idaho (email@example.com).