First hollow stem (FHS) occurs just prior to the jointing growth stage and is the optimal time to remove cattle from wheat pasture. This is the optimal time because the added cattle weight gains associated with grazing past first hollow stem are not enough to offset the value of the reduced grain yield (1-5% loss every day past FHS). With the warmer than normal temperatures throughout the beginning of this year and the forecasted warm temperatures, it is likely we will start seeing FHS occur for some of our “early FHS” wheat varieties in Oklahoma in the next 7-14 days, especially towards the southern border.
One of the moving targets each year is determining when to start scouting for FHS. To help combat this, the First Hollow Stem Advisor was developed by researchers at Oklahoma State University. This is an online tool available on the Mesonet website, https://www.mesonet.org/index.php/agriculture/category/crop/wheat/hollow_stem_advisor. This tool uses soil temperature data to show the current probability of FHS occurrence, as well as 1-week and 2-week projections (detailed information on how this works can be found here). 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 level is reached (green color). Because stem elongation will begin moving quickly as the temperature warms up, starting your scouting at the 5% level will help give you the time it takes for making the necessary preparations for removing the cattle 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 a multi-year period (e.g., 10 years), FHS has occurred by that date in 50% of those evaluated 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 OK, I have generated some statewide maps below. For producers in areas of southeastern and south central OK who planted an “early” wheat variety (e.g., Gallagher), now would be the time to go out and start scouting for FHS (Figure 1).
Figure 1. Current FHS probabilities for “early” wheat varieties.
Looking at the 1-week projection for “early” varieties, you can see how the probabilities have increased, and producers in areas further north should begin scouting (Figure 2).
Figure 2. One-week FHS projection (i.e., through February 8) for “early” wheat varieties.
For producers who planted “middle” or “late” FHS varieties, the 1-week projections indicate producers across much of the state still have a little bit of time yet before beginning to scout. However, producers along the southern border will need to begin scouting (Figure 3).
Figure 3. One-week FHS projections (i.e., through February 8) for “middle” (top) and “late” (bottom) wheat varieties.
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 of hollow stem present (see picture below), it is time to remove cattle. 1.5 cm is about the same as the diameter of a dime.
- More detailed information on FHS can be found at wheat.okstate.edu under ‘wheat management’ then ‘grazing’ or by clicking here.
The first hollow stem growth stage is reached when there is 1.5 cm of hollow stem (about the diameter of a dime) below the grain head. Photo by Dr. Jeff Edwards.
Similar to previous years, we will monitor occurrence of FHS in our wheat plots at Stillwater and Chickasha and report the findings on this blog.