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Division of Agricultural Sciences and Natural Resources

Tool available to help wheat producers make decisions

STILLWATER, Okla. – Timing is everything when trying to get as much bang for your buck as possible in the wheat fields. Wheat producers in Oklahoma have historically circled March 15 on their calendars to remember to pull cattle from the fields.

Waiting much longer than that would result in a drastic decrease in yield.

Research has shown that First Hollow Stem, a particular growth stage in winter wheat, is the optimal time to pull cattle off wheat to prevent yield loss. Using Mesonet weather and soil data, as well as FHS observations from 1995-2012, researchers at Oklahoma State University have developed a tool for producers to consult when deciding how long to leave cattle on their wheat fields.

“Grazing too long will reduce wheat yields, but removing cattle too early will reduce the profit potential of the stocker cattle enterprise,” said Jeff Edwards, head of OSU's Department of Plant and Soil Sciences. “Finding the correct balance between these two factors has been the subject of investigation for decades.”

Available on the Mesonet website (, the FHS Advisor is located in the Agriculture section, under both the “Crop/Wheat” and “Livestock/Cattle” tabs. A guide on how to use the Advisor is located in the “Learn More” section of the website.

The tool utilizes a soil temperature-based model to predict when FHS will occur.

“Looking at a variety of weather and soil variables, we found that 4-inch soil temperatures under vegetative cover were best correlated to FHS dates,” said J.D. Carlson, agricultural and fire meteorologist in the department of biosystems and agricultural engineering at OSU, and developer of the models used in the tool. “The Advisor includes separate models for three different FHS categories of wheat varieties – early, middle and late.”

By visiting the website, producers can select their wheat variety to determine its category. Then maps, graphs and tables will provide information on the probability of FHS occurrence.

“Three maps are available for each FHS category,” Carlson said. “They include a current map of observed soil heat unit accumulations since model start date, projected one-week soil heat unit totals and projected two-week soil heat unit totals.”

The projected maps employ soil heat units based on 14-year daily averages of observed Mesonet soil temperatures over the next seven or 14 days from the current date. To arrive at these projections, the soil heat units over the next seven and 14 days are then added to the current heat totals.

In addition to soil heat unit totals, probabilities for FHS are shown. A color scheme is used to show these levels of probability – blues for FHS probabilities less than 5 percent, greens for 5 percent to 10 percent, yellows for 10 percent to 25 percent, oranges for 25 percent to 50 percent, reds for 50 percent to 75 percent and browns for more than 75 percent.

“We recommend scouting for FHS in ungrazed fields once the 5 percent probability levels (greens) start occurring in the grower’s area, as FHS development starts to speed up at that point,” Carlson said. “For those who don’t scout, we recommend removing cattle by the date the 50 percent level is reached.”

A 50 percent probability level means that over an extended multi-year period (e.g., 100 years) FHS would have occurred by that date in 50 percent of those years. The same interpretation applies for other percentage values.

A detailed video on how to use the First Hollow Stem Advisor is available online at

A SUNUP video is available at


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Sean Hubbard
Communications Specialist
Agricultural Communications Services
145 Agriculture North
Oklahoma State University
Stillwater, OK 74078
Phone: 405-744-4490
Fax: 405-744-5739

Oklahoma State University - Stillwater, OK 74078