The main period for rust risk is largely over for most spring-seeded cereals. Typically, the greatest impacts occur when rust arrives prior to head emergence. Arrival of rust after head emergence and during the grain filling period will have a lower impact, although low to moderate yield losses can occur for susceptible varieties.
Sources of rust are primarily from the Pacific Northwest (stripe rust), Texas/Oklahoma (leaf, stripe, stem, crown rust), and the Kansas/Nebraska (leaf, stripe, stem, crown rust) regions of the USA. However, once crops in these regions start to mature and then are harvested they no longer represent a significant source or cereal rust for Prairie cereal crops. As of July 16, 2023 winter wheat harvest in TX/OK is largely complete, while 71 and 21% of the winter wheat in Kansas and Nebraska has been harvested, respectively (https://quickstats.nass.usda.gov/results/EDA8B6A4-E4E5-32B1-9FFB-E39C78983A28). The oat crop in Texas has largely been harvested, while as of July 16, 2023 63% of the Oklahoma oat crop has been harvested (https://quickstats.nass.usda.gov/results/8149A43F-DEFA-3B0C-9EBC-4F9CF73B2ACE).
Although the Texas to Nebraska corridor is the initial source of cereal rusts from the USA for the eastern Prairie region, rust development in the Northern Great Plains may represent a later and closer source of rust. The most recent USDA Cereal Rust Bulletin (#5, July 14, 2023) indicates detection of trace levels of stem rust in central and south-central South Dakota in research and commercial fields. Dr. S. Wegulo reported very low levels of stem rust in research plots from Cheyenne County in the western part of Nebraska (Cereal Rust Bulletin, Dr. S. Wegulo, University of Nebraska-Lincoln, Cereal Rust Survey Update from Nebraska, July 18, 2023). Stem rust was also reported on July 11, 2023 in rust monitoring plots in east central and south central Minnesota. Levels were trace, although increased levels were found on susceptible test lines. Leaf rust was also recently reported in South Dakota during the second week of July in eastern, central and south-central regions. Levels appeared to be generally low. Some leaf rust was also reported in Minnesota research trials, but levels are considered to be amongst the lowest levels observed compared to previous growing seasons. In July, crown rust was reported from the Brooking County area of South Dakota, while reports were also received from research trials in multiple Minnesota locations including the Fergus Falls, Waseca, Becker, Montgomery, and Rochester regions.
For growers in the western Prairie region, stripe rust has been reported in the Kalispell area, and although levels were severe it was from a experimental line. In central and south-central South Dakota, very low levels of stripe rust have been reported from research trials.
Although the cereal rust season for 2023 is largely over, recent reports of stripe, leaf and/or crown rust from the Northern Great Plains states and the Kalispell region of Montana may represent somewhat of a risk for Prairie producers, but levels in source areas are generally low and mainly from research trials. Prairie farmers and consultants may want to consider keeping an eye out for cereal rust development, especially in later fields planted to susceptible varieties and where localized rainfall events have occurred.
This is the last PCDMN rusk risk report for 2023. We recognize that 2023 has been a very challenging year in terms of moisture availability for farmers in many Prairie regions; hopefully harvest 2023 progresses smoothly and growing conditions in 2024 are better.