Wheat Stand Assessment

By Delbert G. Voight

If there is one thing to have learned over the past 30 years, it’s that each spring is similar, yet the timing can be vastly different. For this reason, it can be best to use growing degree days and/or heat units to determine what and when a management tactic should be used for crop production. During spring, we often experience a couple weeks of advanced growth and growers begin asking themselves about moving up applications which may or may not prove useful for yield and profit. This article is focused on assessing wheat on the need for action like weed control or nitrogen applications.

In terms of questioning nitrogen applications, the answer is always, it depends. In fall of 2022, we had early planted wheat and then we had late planted wheat. This makes a tremendous difference when determining how to manage those planting dates in the spring. A grower will need to assess the stands for tillering and population for both plantings and then base decisions off what is observed in the field. Late winter/early spring is the time to do that management.

When the weather is warmer in the late winter, it often makes growers think about nitrogen applications. After walking wheat fields in 2023, most are showing above 80 tillers per square foot using the third method outlined below. That would indicate that a top dress of N now is not recommended at this time. Growers might find their fields are below the desired tillering and need to consider top dressing based on their own stands.

There are articles referencing the impact of freezing on wheat as well as vernalization in spring planted wheat. To that end in early 2023, while we may be ahead on development, temperatures can turn cold which reduces our accumulated heat units and at a sensitive stage in the wheat growth which can impact final yields. So, by only making N applications to thin stands to encourage some tillering, we can avoid damage to our well-developed stands. Adding N would hasten growth stages too quickly which could result in a potential hit to developing heads when another short duration cold spell hits. Follow along below to assess your stands. Perhaps watch the video in the credits all the way through as well to better explain the how to of doing this in the field.

Additionally, while growers are out there looking to assess stands also check 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 really moving forward in stands that did not receive an herbicide in the fall while those that did are extremely clean.

Determining Plant Populations, Tiller, and Head Counts Plant Populations

There are three methods to do the assessment. Pick one and assessment a few fields with varied history and you might find some large differences in how the stands are responding.

First Method

The first one requires and yardstick or dowel rod 3 ft. in length.

1. Make spring stand counts before green-up of the plants occurs to determine if winter damage has reduced the initial plant population obtained in the fall. Count only whole plants, not tillers. Fields with stand counts below 15 plants per square foot have less than 75 percent yield potential (Table 1) and probably should not be kept but used instead for planting corn or soybeans. If stand counts are adequate to keep but somewhat reduced from optimum, consider an early nitrogen application.

Table 1: Wheat Yield potential based on plants per square foot

^a This provides and estimate of the relationship of 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.

2. 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 well-spaced around the field. Record all numbers.
5. Average all the stand counts from the field.

3. Last, calculate plants per square foot with the following equation:

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

Second Method

A second method to counting stands is to determine the length of row needed to equal one square foot (Table 2). Mark the needed length on a dowel rod or stick and then count the plants in a row.

Table 2: Length of row needed for 1 sq.ft.

A third method from Kentucky Extension is to count the plants, or tillers in 1, 2 or 3 feet of row and use Table 3 to determine stands. 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. To determine tiller numbers, count all stems with three or more leaves. 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.

Table 3. Wheat Stand Count Table

Final Thoughts

As you assess your fields you may find large areas of the field may be drowned out in low lying spots. If these areas 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 and or soybeans depending on which herbicides were applied and their respective replant restrictions.

Most fields are breaking dormancy at the time of this writing which is extremely early for most years.  As the plant develops the small head will appear in a few weeks as illustrated below this, then, becomes critical not to damage from frost, herbicides, burning with N etc. Finally, growers should check the presence of heaving or the pushing of the plant up out of the soil likely on more clay soils with limited snow cover there was some heaving of the crown out of the soil that I observed this spring.  I saw exposed roots and this becomes an issue if herbicides are applied and in some cases injure the expose roots that become covered by certain ALS herbicides, just another aspect to check in the field. By making some key observations now and adjusting to the developing weather wheat stands can be maintained to support maximum yields and profits. 

Credits 

This article seeks to give one some numbers with which to base some decisions on. Tables in this article and other information were obtained from the a Comprehensive Guide for Wheat Management in Kentucky developed by University of Kentucky Extension Another available resource is a video, Assessing Wheat Stands for Yield Potential and Nitrogen Application Timing, created by John Rowehl and Del Voight shows the use of one assessment method.