Stripe rust continues to be a top scouting priority for many wheat farmers in Kansas. The disease was reported for the first time this season about 7 to 10 days ago in parts of southeast and south central Kansas. Additional scouting efforts this week indicate that the disease is now established at low levels in many fields in the central region of the state (Figure 1). The disease was also reported on upper leaves of wheat in the southeast corner of the state. Currently, stripe rust is generally reported to be in the lower or middle canopy of wheat in central Kansas.
The stripe rust infections we are seeing now likely became established about two or three weeks ago, during a period of weather that was highly conducive to the disease. Stripe rust is favored by temperatures between 45-55 F and extended periods of high relative humidity. Many of the areas we are seeing stripe rust in now had more than 70 hours of favorable temperature and humidity between March 23 and April 6 (Figure 2). Some areas had more than 100 hours of favorable conditions.
Interestingly, the weather in recent weeks was less conducive for the disease. The development of stripe rust can be suppressed by warm temperatures, and disease tends to slow when temperature is consistently above 75F. Night time temperatures are particularly important because this is when new stripe rust infections take place. We often see the development of stripe rust begin to slow when night time temperatures are above 60 F and temperatures during the day exceed 80 F for multiple days. Most areas of the state have reported more than 10 hours of temperature above 75F between March 31 and April 14 with parts for southeast and southwest Kansas reporting between 20-31 hours of suppressive temperature for the same time period. Unfortunately, this probably was not enough to suppress the development of stripe rust for long.
The 10-day weather forecast for many areas of the state indicates that temperature and moisture conditions are likely to favor continued development of stripe rust. There is a moderate to high risk of central and southeast Kansas having a severe problem with stripe rust this year. Growers in central Kansas should be actively scouting fields for stripe rust, and making plans to apply a fungicide if the disease is established in their fields.
Fields with good yield potential and seed production fields would be a top priority for a fungicide application because of the generally higher value of grain than general production fields. Varieties such as Armour, Everest, LCS Pistol, LCS Wizard, Garrison, Ruby Lee, and WB-Redhawk are known to be highly susceptible to stripe rust and should also be a top priority. Other highly susceptible varieties include Byrd, Denali, TAM 111, and TAM 112 -- each of which is grown primarily in western Kansas.
For more information about stripe rust identification and fungicide options consider the following publications.
Rust Identification: http://www.bookstore.ksre.ksu.edu/pubs/MF2919.pdf
Fungicide product efficacy: http://www.bookstore.ksre.ksu.edu/pubs/EP130.pdf
Making fungicide decisions: http://www.bookstore.ksre.ksu.edu/pubs/MF3057.pdf
Erick De Wolf, Extension Plant Pathology
Romulo Lolatto, Wheat and Forages Specialist
Mary Knapp, Weather Data Library
Chip Redmond, Kansas Mesonet