NDSU Crop and Pest Report

Plant Science

ISSUE 10  July 3, 2002



Even though included in past pest reports, the requests for information on estimating yield keep coming.

Estimating yield in wheat, or any crop, is done based on the components that compose yield and only determines potential; crop yield is determined after harvest. Small errors in counting the components that contribute to yield can result in large errors in the yield estimate.

Yield in small grains is the sum of three components: i) the number of heads in a unit area; ii) the number of kernels that are produced on a head; and iii) the weight of each of those kernels. Kernel weight can not be determined until harvest so a historical average must be used.


(heads/3 ft X spikelets/head X kernels/spikelet X 0.142*)
row spacing (inches)

* Conversion factor that incorporates area, kernel weight and volume.

Using the formula:

  1. Determine the number of heads in three feet of row. Small heads with two or three kernels should not be counted; they will result in biased high yield estimate.
  2. Determine the number of spikelets per head. This should be an average of six or more randomly selected heads. Top and bottom spikelets contribute little to overall yield and should not be counted (Figure 1).
  3. Determine the average number of kernels per spikelet. Small errors in this number result unrealistically high yield estimates; consequently, using a fixed number that accurately reflects long term yield trends best. Usually 2.3 gives the most accurate results, or 2.1 when the crop has been stressed.
  4. Finally determine the drill row width. When unknown simply measure the distance between several rows of plants and use the average. Most double disc drills are set at 6, 7, or 8 inch row spacings. Air seeders place seed in bands that can range from three to five inches wide; in this case the band width plus distance between bands is used. Measure several rows from the left side of the band to the left side to determine the width.

Figure 1.  Wheat spike, arrows indicate which spikelets (top, mid, and bottom) do not contribute significantly to yield and should not be included in number of spikelets per head when calculating yield.

As illustrated yield estimates are subjective. The correlation between an estimate and the final yield is related to how close head and kernel counts are to the real numbers and crop development during the remainder of the growing season. Keep in mind that no field is uniform and yield potential varies tremendously within a single field. To get accurate counts the process should be repeated several times, not less than eight per field.

Duane R. Berglund
NDSU Extension Agronomist




When farmers see extensive tillering in their corn hybrids, they often express concern that the tillering will have a detrimental effect on crop performance. This was the prevailing view in the early 1950's when it was widely believed that tillers if allowed to develop would "suck" nutrients from the main plant and thereby reduce yields. As a result, tillers were more frequently referred to as "suckers" and many farmers actually walked their corn fields to remove tillers. However, since then research has shown that tillers usually have little influence on grain yields and the effects they do have are generally beneficial.

So what causes tillers to appear?

Tillers are lateral branches that form at lower, below ground nodes. Although tiller buds form at each below ground node, the number of tillers that develop is determined by plant population and spacing, soil fertility, early season growing conditions, and the genetic background of the hybrid. Nearly all hybrids will take advantage of available soil nutrients and moisture by forming one or more tillers where stands are thin in the row or at the ends of rows. Tillers are most likely to develop when soil fertility and moisture supplies are ample during the first few weeks of the growing season. They are usually visible by the 6_leaf stage of development. Hybrids with a strong tillering trait may form one or more tillers on every plant even at relatively high populations if the environment is favorable early in the growing season.

Do tillers deprive the main plant of nutrients?

A number of research studies have been conducted to determine "tiller_main plant relationships." Defoliation experiments in the 1930's revealed that defoliated plants that had tillers yielded nearly twice as much grain as defoliated plants that had no tillers. These results suggested that a connection existed between the tiller leaves and the main plant that allowed sugars produced in the tiller leaves to be moved to the ears on the main plants.

More recent research reports have found that there is little movement of plant sugars between the main plant and tillers before tasseling. However, after silking and during grainfill, a substantial amount of plant sugars may move from earless tillers to ears on the main plant. When there are ears on both the tiller and the main plant,

little movement of plant sugars occurs. In this case the main plant and tiller act independently, each receiving sugars from their own leaves. The nubbin ears, which tillers may produce, therefore have no impact on the ear development of the main plant as was once thought.

Should tillering be ignored?

If a particular hybrid shows excellent yield potential and also produces extensive tillers under some growing conditions, it should not be avoided. However, excessive tillering may indicate problems with stand density and plant distribution within the row. If tillering is associated with row gaps and less than optimal plant populations, these are the conditions which need to be corrected to ensure optimal yields rather than selection of the hybrid. Tillering is also caused by the fungal disease "crazy top," which also produces a range of other symptoms. Such tillering is a disease symptom and not beneficial to plant performance.

Duane R. Berglund
NDSU Extension Agronomist




The question has been posted several times this week, "how are the current high temperatures affecting the small grain crop?" A look back at history shows North Dakota state wide average wheat yields go down as number of days over 80EF during the growing season goes up. In general, cool years produce higher yields on average than hot years.

Just how much of the yield reduction in hot years is due to temperature and how much to moisture stress is unknown. However, the crop develops faster when temperatures are high. This has the effect of reducing the number of days the plant can intercept sunlight. Because, sunlight is the driving force of growth a yield reduction can be expected because the plant has less time for development.

In general, yield in small grains can be thought of in these terms: cool days-slow growth-long growing season = high yields, or hot days-rapid growth-short growing season = lower yields. In particular, high temperatures during the 4 to 5.5 leaf stages results in smaller heads, especially when moisture is limiting. Temperatures in the high 90's F and over 100 F can cause sterilization of wheat pollen/anthers during anthesis.

Duane R. Berglund
NDSU Extension Agronomist




Weeds, particularly kochia and Russian thistle, are often overlooked as potential sources of pasture hay or silage. These weeds usually grow even in a dry year. With proper and timely harvest, they can make good to excellent hay.

Kochia is often pastured even in a dry year and if mowed before flowering, makes excellent hay. Kochia yields in South Dakota over a two-year period averaged about 1.75 tons per acre for one cutting. Russian thistle is not as good a pasture forage but does not make acceptable hay if cut in early bloom before the spines appear. Under drought stress, both forages can be high in nitrate particularly on fallow ground but this has not been a major problem. Redroot pigweed often found in the same fields will add to the nitrate problem. Both forages in good condition as hay or silage are high in crude protein, from 10-20 percent. They are generally low in net energy and may require some supplementation with grain when fed.

When Russian thistles (tumbleweed) are over mature, they will make the best feed as silage. The should be wilted, chopped fine and tightly packed for best quality silage. Water can be added to assist with packing.

Donít overlook these two weeds as sources of emergency feed. They require no cost for establishment and have proven feed acceptability. Fields that are to be left for fallow can be checked for weed growth prior to first tillage. If kochia is present, delay tillage and swath or graze weeds. After weed harvest, proceed with normal tillage operations. Four kochia plants per square yard will be sufficient for hay production.

Kochia pasture is readily eaten by cattle, sheep and hogs. A few reports of photosensitization have been reported. Total documentation of only kochia or some other plant or plants in the pasture as responsible is lacking. However, be aware of this potential problem with kochia and use a mixture of forages when feeding rather than pure kochia as a feedstock

Duane R. Berglund
NDSU Extension Agronomist


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