Grass Stem Rust Decision Aid

Location of real-time (and historical) weather stations. We are using 4 automated weather stations (and historical data from several locations) in grass fields in the Willamette Valley. Since weather affects rust development, differences in the weather among locations will result in different rust predictions. Be wary that real-time station data can become easily corrupted - you may want to compare 2 nearby stations to see if they give generally similar results.

The date of scouting and the amount of rust in the field. Disease development is heavily influenced by the amount of rust present early in the spring, so that neighboring fields can differ greatly in summer rust development if they have different spring levels of rust. The scouting estimate should be based on examining about 6 inches of row (for smaller plants), or samples of 10 tillers each (for older plants), taken from at least 10-20 spots in the field. Any observation after April 1 is useful, and the most recent observation is the best. Accuracy of the prediction depends on accuracy of the scouting information.

Only one type per date. Demethylation-inhibitors (DMI) include Tilt, Folicur, and Laredo; Strobilurins (Strob.) include Quadris and Headline. Mixture is a tank mix of a DMI and a strobilurin. The estimates used in these calculations were for labeled rates of Tilt (6 oz/acre), Quadris (9 oz/acre), or Quilt (20 oz/acre, equivalent to 6 oz each of Tilt and Quadris).