ISSUE 16  August 27, 1998

ESTIMATING YIELDS OF ROW CROPS

Corn Yields

There are several techniques for estimating corn grain yield prior to harvest. This version was developed by the ag. engineering department at the University of Illinois and is the one most commonly used. A numerical constant for kernel weight is figured into the equation in order to calculate grain yield. Since weight per kernel will vary depending on hybrid and environment, the yield equation should only be used to estimate relative grain yield. For example, yield will be overestimated in a year with poor grain fill conditions, while it will be underestimated in a year with good grain fill conditions.

Step 1. Count the number of harvestable ears per 1/1000th acre. (Table 1).

Step 2. Count the number of kernel rows per ear on every fifth ear. Calculate the average.

Step 3. Count the number of kernels per row on each of the same ears, but do not count kernels on either the butt or tip that are less than half size. Calculate the average.

Step 4. Yield (bushels per acre) equals:
(ear#) x (avg. row#) x (kernel#)
90

Soybean Yields

Soybean yield estimates are most accurate within three weeks of maturity, but are still only estimates. Assume 2.3 bean per pod.

1.  Determine the number of feet of row needed to make 1/1000 of an acre (Table 1).

2.  Count the number of plants in ten (10) different randomly selected sample areas. Calculate the average.
Avg.=__________=A (plants/A)

3.  Count the number of pods per plant on ten (10) randomly selected sample areas. Calculate the average.
Avg.=__________=B (pods/plant)

4.  Calculate pods/acre by multiplying plant population by pods/plant.
A x B =__________= C (pods/aacre)

5.  Calculate seeds/acre by multiplying pods per acre by an estimate of 2.3 seeds/pod.
2.3 x C=__________=D (seeds/A)

6.  Calculate pounds/acre by dividing seeds/acre by an estimate of 3000 seeds/pound.
D÷3,000=__________=E (lbs/A)

7.  Estimate yield by dividing pounds/acre by 60 pounds/bu.
E÷60 = __________= Yield (bu/A)

Table 1. Length of row equal to 1/1000th acre. An accurate estimate of plant population per acre can be obtained by counting the number of plants in a length of row equal to 1/1000 of an acre. Make at lest three counts in separate sections of the field, calculate the average of these samples, then multiply this number by one thousand (1,000).

 Row width Length of Single Row to equal 1/1000 of an acre (inches) (feet) (inches) 6 7 8 10 15 20 28 30 32 36 87 74 65 52 34 26 18 17 16 14 1 8 4 3 10 2 8 5 4 6

Dry Edible Bean Yields

You can estimate dry bean yields by knowing the number of seeds per pod, pods per plant and plants per 1/1000th of an acre. At the time of counting seeds and pods, the maturity status of each should be determined.

If a seed or pod will not mature, it shouldn’t be counted. Then count the total plants per 1/1000th acre to complete the data collection.

Yield Estimation

Within a representative and uniform plant stand, randomly select five plants each from at least five randomly selected locations in the field.

Keeping all plant data separate, pull and count the pods from each plant and then count the seeds to determine average seeds per pod for all five replications. These data are combined with the average number of plants per 1/1000th acre.

Average number of seeds per pound

Kidneys 900-1000
Pintos 1400
Great Northerns 1600-1800
Pinks/Small reds 1600-2000
Navies/Blacks 3000

Seeds per pound can vary 10-20% for different varieties within a bean class. If available, use reported estimates for seed number per pound for your variety.

The accuracy of yield estimate can be improved by counting seeds and pods from at least 10 plants per replication.

Calculations

1.  (Average seeds per pod) x (average pods per plant) equals average seeds per plant.

2.  (Average seeds per plant) x (plants per 1/1000 of an acre) x (1000) divided by seeds per pound of the variety equals yield in pounds per acre.

Duane R. Berglund
NDSU Extension Agronomist

WINTER WHEAT, WORTH SERIOUS CONSIDERATION

Winter wheat has the potential to be a highly productive crop in North Dakota. Advantages of winter wheat include; more efficient labor and machinery use, reduced weed problems particularly wild oat, and often a higher yield potential. Winter wheat is not without risk, winter survival is a limitation.

Well-developed winter wheat is less likely to suffer from early season moisture stress than spring-planted small grains, since a well-developed root system enables the winter wheat crop to use sub-soil moisture.

Earlier crop development also helps in avoiding some disease and insect pressure. Winter wheat is no more resistant to scab than spring wheat, however, with a three week developmental advantage it may avoid late infection periods that will affect spring wheat. Orange wheat blossom midge only lay eggs in developing heads between head emergence and flowering. Flowering in winter wheat will be complete before the midge emerge and it will effectively avoid the pest.

Well-established winter wheat is more competitive with summer annual weeds than spring cereal grains, resulting in less dependence on chemical weed control. A healthy stand of winter wheat has good ground cover which shades the soil and acts as a strong competitive force against weed growth. Wild oats is rarely a problem in vigorous winter wheat fields.

Planting and fertilizing the crop in the fall lightens spring planting work loads. Since winter wheat will be ready for harvest two to three weeks before spring wheat the harvest work load is also spread out. Spreading out planting and harvest provide more efficient use of machinery.

Winter survival - Winter survival is the most critical factor in successfully producing a winter wheat crop in the Northern Plains. Cultural practices that help ensure winter survival are those that provide snow cover to maintain warmer soil temperatures in the crown area, just above the plant's root system. NDSU research indicates that a minimum of 3 inches of snow cover is necessary to prevent winterkill due to low temperatures. While three inches of snow is sufficient protection during most of our winters, 4 to 6 inches will further reduce the extent of crown injury and increase stand survival.

Several methods can be used to enhance snow cover. Winter wheat can be no-till seeded directly into flax, barley, mustard, sunflower, or other standing crop residues left to catch the snow. Seeding into wheat or durum stubble will increase the risk of some diseases, but even this practice is often preferred to seeding into clean-tilled fields, particularly in more arid areas where disease is less of a problem, since the stubble will enhance moisture conservation and protection from cold weather.

To avoid a "green bridge" for movement of wheat streak mosaic virus, volunteer wheat and grass weeds should be controlled two weeks prior to planting. Grain stubble should be left at least 6 inches tall to obtain the minimum snow cover required. Hoe drills, which permit deeper seed placement and trap snow in furrows over the seed row, are highly recommended for bare fallow, stubble mulch or chemical fallow fields to improve winter survival.

Stands of winter wheat are often reduced due to winter injury. Don’t be hasty to destroy these stands. It may be mid April, or later, before recovery is evident. Remember winter wheat will readily tiller, stands of 8-10 plants per square foot will produce very good yields. Even when a stand of winter wheat is lost the cropping season is not lost, and generally another early season crop can be planted.

Planting - The recommended seeding dates for winter wheat are September 10 to September 30 in the southern half of North Dakota and September 1 to September 15 in northern regions. Planting after the recommended dates may reduce winter survival and grain yields and also delay maturity of the succeeding crop. Planting prior to the recommended date unnecessarily depletes soil moisture reserves, increases risk of disease and may reduce winter survival.

Winter wheat should be seeded at a rate of 1,000,000 viable seeds per acre or about 80 pounds per acre. Higher seeding rates are suggested for late seeding or for poor seedbed conditions.

Only the most winterhardy varieties available should be considered when growing winter wheat in North Dakota. Of the current varieties, Roughrider, Agassiz, Seward and Elkhorn possess the best combination of winterhardiness and yield. See NDSU Extension circular A-574 or the North Dakota Small Grains web page http://www.ag.ndsu.nodak.edu/aginfo/smgrains, for detailed agronomic information on available winter wheat varieties.

Fertilizer applications for winter wheat should be based on soil tests and yield expectations. Winter wheat's nitrogen need in the fall is low and does not exceed the rate that can safely be applied in the drill row at seeding time. Nitrogen applications on snow are not recommended. Snow compaction under wheel tracks destroys snow insulation properties and results in winterkill beneath the track. Movement of N offsite is also a problem on deeply frozen soils when snow melts in the spring.

Phosphorus aids overwinter survival by stimulating root growth and fall tillering. The secondary root system that develops with tillering is essential for a healthy deep-rooted plant capable of withstanding stress. While important, the contribution of phosphorus to overwinter survival is secondary to varietal hardiness and soil temperatures at the growing point in the plant crown.

Additional information is available in NDSU Extension publications: Fertilizing hard red spring wheat, durum, winter wheat and rye, SF-712; Winter Wheat Production in North Dakota, EB-33; The North Dakota fertilizer hand book, EB-65.

Michael D. Peel
NDSU Extension Agronomist

LAWN RENOVATION TIME HAS ARRIVED!

Late August to late September is the best time for lawn establishment or renovation in our area of the prairie. If you are totally fed up with the invasion of sow thistle, quackgrass, curly dock weed, and broadleafed plantain, you can get revenge by killing everything off with a non-selective herbicide like Round-Up® or Kleen-Up®, which both have the active ingredient, glyphosate.

About one week after application, the treated area should be just about completely brown. Touch up any skips with another shot of the non-selective herbicide. The herbicide is most effective if the plant material to be killed off is actively growing and is unmowed. Watering heavily for a few days before the application may be necessary to "soften" the plants up for the kill!

Once everything has turned brown, mow it down and collect the clippings. This may take two mowings; the first at the normal mowing height, and the second at a near-scalping level. Next, rent a power rake, vertical mower, or power dethatcher (generally the same machine, just known by different names), and set it for a depth that will slice into the remaining thatch. Go over the area in two directions, perpendicular to each other. Run the mower with bagger attached, over the turf area again to collect some of the loose debris. I am dead set against disturbing the soil any more than this unless major grade changes need to be made. The reason for this is simple - too many obnoxious weed seeds get pulled to the surface and need to be wrestled with in getting the turfgrass re-established. This in not to imply that there will be no weed germination - there will, but most will be benign and not able to mature and set seed before winter arrives and kills them off.

Select the appropriate quality seed mixture - generally made up mostly of Kentucky bluegrass (55-60%), then the balance made up of creeping red fescue, and perennial ryegrass, sowing at about 3-4 pounds per 1000 square feet. Once the seed is down, drag it in lightly with a broom or leaf rake, and be committed to supplying irrigation for the next 3 weeks. Not all the seed will germinate before winter, and the seedlings that do generally fare well, coming back with vigor the following spring.

Hold off on fertilization until next spring when the grass has begun active growth, unless you happen to be one of those individuals that need to feed something developing! In that case, apply an organic like Milorganite or something similar that will not cause over-stimulation of growth.

Ronald C. Smith
NDSU Extension Horticulturist and Turfgrass Specialist

SPRUCE PROBLEMS

Spruce problems are often very difficult to diagnose and many times can only be described as some type of "environmental injury." Environmental injury can be caused by non-adapted plants, climatic extremes, poor soils, contaminated soils, flooding, drought, herbicides and many other factors. Determining the cause of environmental injury requires looking at the pattern of injury on the entire plant or planting and learning the history of the site. Whenever an insect or disease is not identifiable, the cause of injury is usually noted as some type of environmental injury. Even though many spruce problems are environmental, we do often find organisms of one type or another causing damage to spruce across North Dakota. Four of the more common spruce damaging organisms are Cytospora kunzei (a canker-causing fungus), Rhizosphaera kalkhoffii (a needlecast-causing fungus), Oligonychus ununguis (spruce spider mite), and Pikonema alaskensis (yellow-headed spruce sawfly). The yellowheaded spruce sawfly was addressed in the June 11, 1998 issue of the Crop and Pest Report. The other three will be described here.

Cytospora canker. While blue and Norway spruce are most susceptible, Cytospora cankers occur on all spruce species commonly planted around North Dakota. Symptoms typically first begin as a yellowing of needles on individual lower branches. These needles soon turn brown and eventually fall off after a few months. When the problem is first observed as needles are falling from branches, many people inappropriately refer to the problem as a needlecast (needles are being lost). The term "needlecast" is typically reserved for fungi that infect needles. Therefore this term is not correct because the needles are indirectly affected by the death of the entire branch. Looking at the larger limbs to which the affected needles are ultimately attached, white or light blue resin is often seen on the bark. This is where the canker-causing fungus may be found under the bark. Peeling back the bark will expose diseased wood (brown compared to the normal light color of healthy wood).

Less susceptible spruce species should be planted where Cytospora canker has historically been a problem. When a tree becomes infected with the canker-causing fungus, infected limbs should be removed as soon as possible during dry weather. Pruning sheers should be disinfected with rubbing alcohol between cuts. If infected limbs are left on the tree, the disease may move up the tree from the lower limbs and eventually cause the tree to lose aesthetic, wind control, and noise reduction benefits. Severely affected trees may eventually die. Cytospora cankers are often less severe on healthy trees. Maintain tree health by allowing adequate space when planting, watering trees during drought periods, and preventing root injury (construction, deep tillage, etc.).

Rhizosphaera needlecast. Rhizosphaera needlecast has historically been a greater problem in eastern North Dakota than western areas of the state. Recently, we have seen this disease in two communities in northwestern North Dakota. R. kalkhoffii infects needles during spring. The following spring, needles begin to turn yellow then purplish-brown. Winter injury may cause similar symptoms, but Rhizosphaera needlecast can be positively identified using a hand lens or magnifying glass. The fruiting bodies of R. kalkhoffii will emerge through the normally white stomatal openings in the needles, causing them to appear black under 10X magnification. Similar to Cytospora canker, the disease will often begin in the lower part of the tree and progress up the tree gradually. Unlike Cytospora canker, Rhizosphaera needlecast will not be confined to individual branches, but instead infect areas of needles (such as all the lower needles) and there are often live needles at shoot tips of that have Rhizosphaera needlecast infected trees, whereas all the needles are killed on limbs infected with C. kunzei. Although Rhizosphaera needlecast can cause tree death when it is extremely severe, the greatest losses come in reduced aesthetic, wind control, and noise reduction benefits.

Prevention of Rhizosphaera needlecast begins with planting healthy stock and allowing adequate space for mature trees to develop. This can be difficult in windbreaks, where density is extremely important in wind management. When Rhizosphaera needlecast does develop in established trees, chlorothalonil or Bordeaux mixture 8-8-100 applied once as needles are 50% elongated in the spring and again soon after needles are completely elongated will usually control early infections. For more advanced infections, two years of fungicide treatments are usually necessary.

Spruce spider mite. Spider mites over younger foliage, cause older needles to discolor and drop. Without further investigation, needle drop symptoms caused by spruce spider mite may be attributed to a needlecast disease. Mites will cause tiny yellow or white speckles on needles that can be seen with the naked eye and are easily identified with a hand lens. Spruce spider mites are "cool season" mites and are most active during spring and fall. If temperatures constantly remain over 90°F, these mites will lay eggs and become dormant. We often notice damage during hot, dry summer days. The damage often occurred in the previous spring or fall and became evident under the stress of hot, dry weather. Since miticides are usually more effective against adults than eggs, summer applications of miticides are not always effective. Since the mites are only 0.5 mm long, they are very difficult to see without magnification. As with most spider mites, a good test for spruce spider mites is to place a white piece of paper under needles which are believed to be infested and tap the branch. Mites appear as mobile specks on the white paper. Generally, if ten or more mites are found per sample, some type of control may be necessary. Syringing, cultural control, biological control, and chemical controls are all options that can be used in controlling spruce spider mites. Spraying mites with a forceful jet of water (syringing) can be an effective method for controlling mite populations in home landscapes while maintaining natural predators. Lace wings and lady beetles are naturally occurring predators of spruce spider mites in North Dakota. These predators and predatory mites may be purchased and released to control spruce spider mites. Insecticidal soaps can be used to manage spruce spider mites in warm weather, while horticultural oils (1-2% rate) may be used during the summer and dormant oils (3-4%) rate can be used to kill mite eggs and adults during the spring and fall. Horticultural oils can injure conifers if applied when temperatures are not appropriate. Read the labels carefully. Miticides should be sprayed when adults are active with a follow-up spray 7-10 days after the first spray to control later hatching nymphs.

Marcus Jackson
Extension Forester