Amanda de Oliveira Silva, Small Grains Extension Specialist

The first hollow stem stage (FHS) indicates the beginning of stem elongation, or just before the jointing stage. It is a good indicator for when producers should remove cattle from wheat pasture. This occurs when there is 1.5 cm (5/8”, or the diameter of a dime) of stem below the developing grain head (see full explanation). This is the optimal period because it gives enough time for the crop to recover from grazing and rebuild the canopy. Also, the added cattle weight gains associated with grazing past the FHS are not enough to offset the value of the potential reduced grain yield (1-5% every day past FHS). The wheat variety, severity of grazing, time when cattle are removed, and weather conditions after cattle removal determine how much grain yield potential might be reduced.

The Mesonet First Hollow Stem Advisor was developed by researchers at Oklahoma State University to help predict when FHS is nearing. This is an online tool available on the Mesonet website. This tool uses soil temperature data to show the current probability of FHS occurrence and 1-week and 2-week projections. With this tool, producers can select their variety from a list of varieties that separates them into three FHS categories: early, middle, and late. Then, maps can be generated to provide the probability of FHS based on current conditions and the 1- and 2-week projections. Charts and tables can also be generated for individual Mesonet sites. Created maps have a color scheme to represent the probability of FHS occurrence. When using this tool, it is recommended to start scouting for FHS from a non-grazed part of the field once the 5% probability is reached (green color). Because stem elongation will begin moving quickly as the air temperature rises, starting your scouting at the 5% level will help give you the time it takes for making the preparations for cattle removal by the time FHS occurs. Methods on how to scout for FHS are listed at the end of this post. For producers who do not scout, it is recommended to remove cattle when the 50% probability level is reached. A 50% probability level indicates that over an evaluated period (e.g., 10 years), FHS would have occurred by that date in 50% of those years (e.g., 5 years). The same interpretation is used for other probability levels.

To give an example of what the tool provides and show some of the FHS conditions around Oklahoma, I have generated some statewide maps below. For producers along the southern Oklahoma border who planted an “early” wheat variety (e.g., Gallagher), now would be the time to go out and start scouting for FHS (Figure 1).

Remember that this tool should be used as a proxy to begin scouting for FHS. The best estimate of FHS is still to split stems from plants in each field to determine where they are developmentally. Another word of caution I want to mention when using the tool is to consider when you were finally able to get stand establishment. If this did not occur until the end of September to the beginning of October, this tool may be a little ahead of where your plants are developmentally. In this case, the tool can still give you the cue to start scouting. Checking for FHS in each field will let you know if you do have some grazing time left.

Methods for scouting for FHS:

• Check for FHS in a non-grazed area of the same variety and planting date. Variety can affect FHS date by as much as three weeks and planting date can affect it even more.
• Dig or pull up a few plants and split the largest tiller longitudinally (lengthways) and measure the amount of hollow stem present below the developing grain head. You must dig plants because the developing grain head may still be below the soil surface at this stage.
• If there is 1.5 cm (~5/8″) of hollow stem present, it is time to remove cattle. 1.5 cm is about the same as the diameter of a dime (see picture below).

More detailed information on FHS can be found at wheat.okstate.edu under ‘Wheat Publications’ then ‘Grazing’ or by clicking here.

Similar to previous years, we will monitor FHS occurrence in our wheat plots at Stillwater and Chickasha and report the findings on this blog. Remember that we use an accelerated growth system to report the earliest onset of the FHS stage. Trials are seeded early to simulate a grazed system, but the forage is not removed. Varieties reported here with the earliest FHS date should be the first to monitor in commercial fields. In practice, wheat that is grazed will likely reach FHS stage later than reported here, and differences between varieties will likely moderate.

The latest FHS results for each variety planted in our forage trial at Stillwater and Chickasha are listed below (Tables 1 and 2).

Table 1. First hollow stem (FHS) results for each variety collected at Stillwater. Plots were planted on 09/18/23 but not grazed or clipped. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements. Varieties exceeding the threshold are highlighted in red.

Table 2. First hollow stem (FHS) results for each variety collected at Chickasha. Plots were planted on 09/21/23 but not grazed or clipped. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements. Varieties exceeding the threshold are highlighted in red.