The wheat growing season up to this point has been extremely tough to say the least. The forage situation has been a kick-in-the-knees in addition to taking it on the chin with the grain prices. Trying to get wheat pasture established was hard enough between fighting off the fall armyworm and working around the rain. Then on top of all that after getting a stand established, it has not rained since. As a result, many producers have already grazed as much as they could and have removed their cattle, or they have not even had the chance to graze. For the few producers who still have pasture to graze, leaving some leaf material out there after grazing will be important for having any chance of a decent grain crop. Ideally, there should be a minimum of 60% canopy coverage left. It also does not look like we will have cool and wet conditions after cattle removal to allow the plants more time to recover from the grazing injury. This situation is shaping up to be similar to last year, and that puts even more emphasis on removing cattle from wheat pasture at the right time.

The optimal time to remove cattle from wheat pasture is at a growth stage called first hollow stem (FHS, between Feekes 5 and 6). 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% every day past FHS). The wheat variety, amount of grazing, time when cattle are removed, and weather conditions after cattle removal determine how much total grain yield potential might be reduced.

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. 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 temperature warms up, 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).

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 areas further north should begin scouting (Figure 2).

Figure 2. One-week FHS projection (i.e., through February 22) for “early” wheat varieties.

For producers who planted “middle” (e.g., Duster) or “late”  (e.g., Doublestop) 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 should begin scouting (Figure 3).

Figure 3. One-week FHS projections (i.e., through February 22) for “middle” (top) and “late” (bottom) wheat varieties.

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 for this year especially 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, but 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 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. 

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.