Wheat Stand Assessment

Producers often focus on spring wheat assessments for nitrogen and weed management but forget the importance of assessing wheat for germination and tillering before winter. While both are important, skipping fall assessments can lead to yield reduction that spring management cannot overcome. This article outlines methods for assessing wheat stands and addressing weed and nitrogen concerns in the fall and spring.

Determining Plant Populations, Tiller, and Head Counts

There are three methods to do stand assessments. Pick one method that works for you and your operation. Assess a few fields with varied histories and note any differences in how the stands respond.

A Method from University of Kentucky Extension to Determine Fall Plants and Tillers

This method involves counting the plants or tillers in 1, 2, or 3-foot sections of a row. Then, the stand count can be determined using Table 1. For example, if you count 80 plants in 2 feet, on 7.5-inch spacing, that equals 64 plants/sq foot. This method is useful for assessing fall stands and calculating winter nitrogen recommendations. 

Table 1. Wheat Stand Count Table

Determining Yield Potential in the Spring

Final stand and yield potential are essential for determining winter survivability and spring stand assessment, so completing this before spring green-up is crucial. If taken after spring green-up, the count will not represent the initial plant population obtained from the fall. 

There are two ways to determine plants per square foot.

The first method requires a yardstick or dowel rod three feet in length.  

1. To determine the number of plants per square foot:

1. Use a yardstick or cut a dowel rod to a 3-foot length.
2. Place the measuring stick next to an average-looking row and count all plants in the 3-foot length of the row.
3. Record the number.
4. Repeat the counting process in at least five other locations around the field. Record all numbers.
5. Average all the stand counts from the field.

2. Calculate plants per square foot with the following equation:

1. (average plant count × 4)/row width in inches

The second method uses a known distance of planted row and row spacing. 

1. Using Table 2, determine the dowel rod or stick length needed as a measuring device based on your row spacing. i.e., if you have 7.5-inch row spacing, you would need a 19.2-inch stick. 

1. Place the cut dowel or stick next to an average-looking row and count all plants in that row length. 
2. Record the number. This number equals plants per sq. ft.
3. Repeat the counting process in at least five other locations around the field. Record all numbers.
4. Average all the stand counts from the field.

Once the plants per sq. ft. has been calculated for the final stand, this can be compared with the information in Table 3 to determine potential yield. If the field is averaging 19 plants per square foot, yield potential is 90-95%. If the average is 10 plants per square foot, yield potential will be closer to 55%. 

^a This provides an estimate of the relationship of the wheat stand to yield potential and is only a guide. Many factors (plant vigor, weather, disease, fertility management, planting date, and variety) influence how a wheat stand ultimately responds to achieve its final yield potential.

Interpreting Stand Assessment

Fall Assessment and Applications

As conditions become warmer in late winter,  growers may consider applying nitrogen to tillering wheat. Nitrogen is best applied when crops are actively growing. Therefore, top dressing nitrogen is recommended for the late winter or early spring and not during the late fall or winter. Growers might find their fields below the desired tillering and need to consider top dressing based on their tiller count.

Taking a tiller count, which includes main shoot and tillers at Feekes 3 (roughly Zadoks 22 through 26), is the first step in all fields for determining nitrogen needs in late winter or early spring. Research suggests that tiller counts below 70 per square foot indicate the need for nitrogen at Feekes 3. At recommended populations, many plants will have only three to four stems (main shoot plus two to three tillers, Zadoks 22 or 23). Thus, 70 to 100-plus tillers (stems) per square foot at Feekes 3 are considered adequate.

Research suggests that adding 60 lbs. of nitrogen to fields with 20-29 tillers and reducing rates to 40 lbs. on fields with 40-49 tillers will increase winter tillering and spring production. Fields with tillers between 50 and 70 may still see responses from nitrogen applications, but that will be more variable and less predictable depending on weather and soil type. Something else to consider is that adding N would hasten growth stages too quickly, which could result in potential damage to developing heads if another short-duration cold spell occurs. For this reason, it is best to only apply nitrogen to thin or underdeveloped stands and not fully developed stands (70+ tillers).

Additionally, while assessing stands, be sure to scout for weed growth. When scouting in a burst of warm weather during the late winter, it is not uncommon to find speedwell (in bloom), chickweed, and dead nettle moving forward in stands that did not receive an herbicide in the fall, while those that did are extremely clean.

Spring Assessment and Applications

The onset of spring temperatures can often be unpredictable. Therefore,  growing degree days may be used to determine if and when a management tactic should be used for crop production. During spring, we often experience a couple of weeks of advanced growth, and growers begin asking themselves about moving up applications, which may or may not be helpful for yield and profit.

Fields with stand counts below 15 plants per square foot have less than 75 percent yield potential (Table 3) and should not be kept but used instead for planting corn or soybeans. Consider an early nitrogen application if stand counts indicate that the crop is adequate to keep but reduced from optimum.

As you assess your fields, large areas may be drowned out in low-lying spots. Another thing to evaluate and monitor is the heaving or the pushing of the plant out of the soil. Heaving is more prevalent on clay soils with limited snow cover but can be possible anywhere with an intense freeze and thaw cycle. The exposure of roots can become an issue if herbicides are applied. Wheat stands can be maintained to support maximum yields and profits by making some key observations now and adjusting to the developing weather. If areas affected by heaving or thinning stands make up most of the field area, it might be worthwhile to consider rotating out of wheat and into a corn crop to utilize any N that may have been applied. Depending on which herbicides were applied and their respective replant restrictions, soybeans may also be planted.

Interested in Learning More about Winter Wheat Management? 

If you are interested in learning more about winter wheat management, tune in to Season 2, Episode 8 of the Agronomy Highlights Podcast. In this episode, Penn State Extension agronomy experts tackle the management of winter wheat from two perspectives: general agronomics and soil fertility. From planting dates and seeding rates to nitrogen applications in fall and spring, this episode covers all the basics of successfully growing a crop of winter wheat. Listen on our website, Spotify, Apple Podcasts, or wherever you listen to podcast content. 

Credits 

This article seeks to give some quantifications on which to base some wheat management decisions. The tables in this article and other information were obtained from the Comprehensive Guide for Wheat Management in Kentucky developed by the University of Kentucky Extension.