NDSU Crop and Pest Report

Plant Science


ISSUE 12   July 22, 2004

YELLOW SOYBEANS SLOW TO GREEN UP

Recent wet conditions in soybean fields have, in some cases, resulted in very yellow soybeans in many growing areas in eastern North Dakota. Heavy rains and excessive moisture is the primary cause. However, many different causes or a single stress may be contributing to the change of color. Start by checking the variety planted and the soil pH. Iron chlorosis is showing up in many of the fields, especially those planted to varieties with poor iron chlorosis tolerance and on soils having a pH of 7.8 or higher. Iron chlorosis can be accentuated with soil wetness that increases bicarbonate solubility in soils and may elevate soluble salt levels, further stressing the soybeans. Varieties are rated as to iron chlorosis tolerance in the Extension Circular entitled "Soybean Performance Testing 2003, Cir. A- 843. The information can also be found at the web site:

http://www.ag.ndsu.nodak.edu/plantsci/rowcrops/soyall.htm

Any herbicide applications that were made right around the first trifoliate leaf stage on soybeans may also contribute to the stress on the soybeans if the plants were already stressed with iron chlorosis, varying temperatures, wet feet, insects, weed competition, disease, soil compaction or other previous damage such as hail. Generally, yellowing quickly disappears from soybeans once drying occurs and warmer sunny weather as has been forecast this week. However, this year the problem seems to be still lingering. Top growth on the soybean plants should now begin to green and continue if the plants are to have good recovery. Hopefully green color should return within a week or two if the wet weather discontinues and with higher temperatures and sunshine.

 

HARVESTING DRY PEAS

Pea growers need to carefully monitor the crop as it nears maturity in order to harvest on a timely basis. Lots of first time growers in the state this year. Acreage in North Dakota has increased to 280,000 acres which is tops in the nation and is 58% of the planted dry pea acreage in 2004. Harvest timing is especially important if the crop is to be marketed as seed, or to meet contract specifications for human food or specialty feed markets.

Field pea generally reaches physiological maturity in 85 to 105 days depending on the variety. Field pea may be swathed before combining or straight (direct) combined. Peas are normally swathed if a variety with prostrate type of growth is grown, there is uneven crop maturity, or heavy weed pressure is present. When swathing peas, vines and pods should be a yellow to tan color. The crop matures from the bottom pods upward. Yellow-cotyledon peas should have seed that has turned yellow in color.

Field peas should be combined when the seed contains 14 to 20% moisture, to reduce splitting and cracking of the seed coat. At this moisture level, the seeds are firm and no longer penetrable with a thumbnail. Also, pea vines must have turned yellow (no green color present) otherwise harvest will be extremely difficult.

Straight combining is possible depending on variety grown and harvest equipment available. Short-vine and semi-leafless pea grain varieties have characteristics that are adaptable to straight harvesting compared to varieties with indeterminate and prostrate-vine growth. For example, semi-leafless peas have a more open canopy, remain erect longer, and dry down more rapidly after a rain or heavy dew compared to conventional vining varieties.

Direct harvesting can be accomplished using a combine header with a floating cutter bar or a flex header. Also, attachments such as lifter guards and pickup reels reduce losses and improve harvest efficiency. Direct harvesting of weak and prostrate vine cultivars is most efficient with a an aggressive pickup attachment and a lead coulter on a standard combine.

Correct combine settings and operation are important to maintain seed quality. Low cylinder speeds of 350 to 600 rpm, should be used to minimize seed cracking or splitting. Initial concave settings of 0.6 inch front clearance and 0.2 inches at the rear are suggested. Also, adjust combine settings as weather and harvest conditions change. Combine and all portable augers should be operated at full capacity and at low speeds to minimize seed coat damage and reduce splits.

 

CATTAIL SPRAYING TO CONTROL BLACKBIRDS

North Dakota and South Dakota sunflower producers have the opportunity to reduce cattail stands in wetlands again this year through a unique program directed by USDA’s Wildlife Services. Cattails are the perfect habitat for breeding and migrating blackbirds. USDA sprays the cattails by air with an EPA approved herbicide at no cost to the producer. The removal of cattails opens the wetlands and helps to disperse large concentrations of blackbirds which feed on sunflower fields. The best time to spray is in late July and August. A treated wetland often remains open for four years and longer. Applications for the program must be received by July 30, 2004. Interested growers need to contact USDA at 701-250-4405 or call the National Sunflower Association at 888-718-7033. Source - NSA Newsletter - July 13, 2004.

Duane Berglund
NDSU Extension Agronomist
duane.berglund@ndsu.nodak.edu

 

ESTIMATING WHEAT YIELD BEFORE HARVEST

The wheat crop is nearing harvest and most yield components are now more or less fixed. Therefore, one can estimate the yield of wheat with a fair degree of confidence. Many experienced agriculturalists can accurately estimate yields by just "eyeballing" the field. For those of us less experienced and for those whose eyeballing method misses reality by a wide margin, I would suggest the following procedure for estimating wheat yield before harvest. This procedure is an adaptation of a procedure previous described by Dr. Duane Berglund, NDSU Extension Agronomist. You will be required to walk out into the field and take counts on a representative areas of the field of interest. In a uniform field you should sample at least 8 areas that do not include head rows and that are representative of the field as a whole. For fields that vary considerably in their yield potential you will need to make more measurements and include samples from the various areas of the field that differ in yield potential. The procedure describe is based on measuring various components of yield in a defined area and using "average" values for those components that are not so easily measured in the field to enable a quick and easy estimation.

For each of the sample areas described above do the following:

1. Count the number of heads in a three-foot row. If the seeder placed seeds in paired rows or in a band, count all of the heads in both paired rows or in the entire width of the band. Do not include heads that are small and have few kernels or that emerged late and will not mature before harvest.

2. From the row of heads that was just counted, select 6 heads randomly. Count the number of spikelets on each of these heads, omitting the bottom-most and top-most spikelets and average the numbers to get the average number of spikelets per head.

3. Determine the distance between the rows. If the row spacing of the seeder is not known, measure the distance between several rows or if bands of seeds were sown, measure the distance between the left side of one band to the left side of an adjacent band.

4. Use the above numbers in the following formula to estimate bushels per acre:

(Heads/three ft row X avg # of spikelets/head X 2.3 X 0.142)
row spacing (inches)

The value 2.3 is the number of kernels that develop on average in a spikelet. If the crop is severely stressed use 2.1 instead of 2.3. The other number, 0.142, is the product of several other numbers that takes into account the average weight of a kernel and converts the output of the equation into bushels per acre.

As an example, if you counted 70 heads in a three foot length of row with 7 inch row spacing and the average number of spikelets per head were 10, then the estimated yield for this area of the field would be: (70 heads/three ft row x 10 spikelets/head x 2.3 kernels per spikelet x 0.142)/7 inch rows = 32.7 bu/acre.

There are other methods of estimating yield that are more input intensive. Generally, the above described procedure does a good job of estimating wheat yield in most situations.

 

LODGING IN SMALL GRAINS

In much of the state conditions have been excellent for spring wheat growth. In these regions yield is expected to be as good and in some cases better than last year. With these favorable growing conditions, however, wheat plants are taller than normal, and with spikes gaining weight during grain filling are now prone to lodging. Depending on when it occurs, lodging can significantly reduce yield and even if yield is only slightly reduced, negatively impact grain quality. Unfortunately, there is really nothing that can be done at this point to reduce the impact of lodging as "lodging management" begins early in the season.

What is lodging?

Lodging is the term used to describe a crop when its stems have partially or completely fallen over from their normal near vertical orientation. There are two types of lodging. Root lodging that occurs at the base of the plant as a result of roots failing to anchor the plant. Root lodging is the most common of the two types of lodging. Stem lodging occurs when the stem breaks. Stem lodging can occur at any point in the stem, but most commonly occurs at the lower portion of the plant and usually later in the season as the plant begins to mature and stems become brittle and the spike accumulates weight. When root lodging occurs early (i.e. before grain filling), it is possible for some stems to partially erect themselves. This is accomplished by the plant bending at one of its nodes. These nodes tend to enlarge and have the appearance of "elbows".

What are the cause of lodging?

Lodging results from the combination of a number of factors, and is usually induced by strong winds and rains. Lodging is most common in the later part of the crop’s growth, particularly during grain filling as more of the plant’s weight is shifted to the upper portion of the plant. The main factors that predispose a crop to lodging are:

  • High levels of nitrogen - N causes lush growth and heavier plant tissue. Excessive N can cause stems to be weak.
  • High seeding rates - With high plant densities there is less space for roots of individual plants, therefore, root systems are usually less extensive and less well anchored. There has been a trend towards heavier seeding rates in small grains in an attempt to intensify production. One of the down sides of excessive plant populations is an increase in the potential for lodging.
  • Wet soil conditions - Excessive soil moisture limits root development. Furthermore, roots in these types of soils often suffer from root rots. Wet soils do not anchor the roots of a plant as tightly as a dry soil.
  • Tall plant types or varieties with poor straw strength - Taller plant types are more prone to lodging as their center of gravity is higher than shorter plant types. Almost without exception, short varieties (dwarf types) are the most resistant to lodging. Within all plant height types, however, there is variability for lodging resistance and some varieties are just more prone to lodging than others. Although modern breeding programs screen their materials for lodging resistance, that does not mean that they all will have the same level of lodging resistance, nor does it mean you can manage them poorly and expect them to remain standing.
  • What kind of losses are associated with lodging?

    Yield losses resulting from lodging vary considerably. Some data suggests that losses up to 40% can occur if lodging occurs during the 10 days following heading. Grain yield losses will be much less if the grains are nearly filled. However, kernel damage and sprouting can occur in lodged fields that become wet. There may also be losses in labor as combining lodged fields takes longer.

    What can you do to prevent lodging in the future?:

    A number of farmers have expressed interest in knowing how they might manage their fields in the future so that they do not have the problems of lodging that they are experiencing this year. Some suggestions are:

  • Avoid excessively high seeding rates.
  • Keep N applications at a reasonable level and make sure that P and K levels are adequate.
  • Grow a more lodging resistant variety. If you consistently have problems with lodging, use varieties that are described as semi-dwarf with strong straw strength in the NDSU Varietal Selection Guides.
  • Use crop rotations and other integrated pest management practices to reduce the incidence of root rots.
  • Joel Ransom
    NDSU Extension Agronomist - Cereal Crops
    joel.ransom@ndsu.nodak.edu


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