C.O.R.N. Newsletter 2010-25

Dates Covered: 
August 10, 2010 - August 16, 2010
Editor: 
Andrew Kleinschmidt

Wheat Seed Treatments 2010

Seed treatments can play an important role in achieving uniform seedling emergence under certain conditions. Seed treatments can protect seeds or seedlings from early-season diseases, and fungicides are available to provide such protection. However, seed treatments should not be considered a cure-all for the selection of poor quality seed lots. Seed treatments will not increase poor germination due to excessive mechanical damage, poor storage conditions, genetic differences in variety, or other damage.

Head scab and Stagonospora glume blotch were at high levels in many fields this year, therefore growers need to limit losses due to these and other seed-borne pathogens by treating seed. In addition, be sure to use crop rotation and plant resistant or less susceptible varieties. Be especially concerned that saved seed may be contaminated. If head scab or Stagonospora was present at high levels in your wheat field do not use that grain for seed. These seed infesting fungi will contribute to poor quality seed resulting in reduced yield and lower test weight.

However, if you absolutely have to use scabby wheat for seed, cleaning, germ test, and fungicide seed treatment are absolutely necessary. Use the level of scabby kernels and test weight as your guide. You can determine the percent scabby kernels of you lot by using the visual chart found on the Field Crops Disease website. Cleaning will get rid of light, scabby material, and this will naturally increase the test weight of the lot. If you can increase a test weight to about 56 lb/bu (after cleaning) and your germ is above 80%, then you have decent quality seed. Gravity table would be your best option for cleaning.  In addition to cleaning and treating, seeds should be stored under cool, dry conditions until planting to prevent mold development. Blending of scabby wheat with healthy wheat is another good option to increase the overall quality of the lot.

The systemic fungicide Dividend Extreme is effective in controlling seed-borne Stagonospora, but it is more effective against seed-borne scab at the higher rate than at the lower rate. Products containing Raxil used at the labeled rates are effective against seed-borne Stagonospora and have relatively good activity against seed-borne scab.

See the following websites and the pdf file for more on rating scabby wheat and fungicide seed treatment:

http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/WheatKernels2.htm           

Wheat seed treatment chart 2010.pdf       

While examining ears to determine potential grain yield, growers may encounter various ear development problems that may impact yield at harvest (https://agcrops.osu.edu/specialists/corn/resources/of-interest/AbnormalCornEarsPoster_000.pdf). Troubleshooting these corn ear disorders now rather than at harvest may give growers more time to diagnose likely causes of these problems.

Two procedures that are widely used for estimating corn grain yields prior to harvest are the YIELD COMPONENT METHOD (also referred to as the "slide rule" or corn yield calculator) and the EAR WEIGHT METHOD. Each method will often produce yield estimates that are within 20 bu/ac of actual yield. Such estimates can be helpful for general planning purposes.

THE YIELD COMPONENT METHOD was developed by the Agricultural Engineering Department at the University of Illinois. The principle advantage to this method is that it can be used as early as the milk stage of kernel development, a stage many Ohio corn fields have probably achieved. The yield component method involves use of a numerical constant for kernel weight which is figured into an equation in order to calculate grain yield. This numerical constant is sometimes referred to as a "fudge‑factor" since it is based on a predetermined average kernel weight. Since weight per kernel will vary depending on hybrid and environment, the yield component method should be used only to estimate relative grain yields, i.e. "ballpark" grain yields.

When below normal rainfall occurs during grain fill (resulting in low kernel weights), the yield component method will OVERESTIMATE yields. In a year with good grain fill conditions (resulting in high kernel weights) the method will underestimate grain yields.

Step 1. Count the number of harvestable ears in a length of row equivalent to 1/1000th acre. For 30‑inch rows, this would be 17 ft. 5 in.

Step 2. On every fifth ear, count the number of kernel rows per ear and determine the average.

Step 3. On each of these ears count the number of kernels per row and determine the average. (Do not count kernels on either the butt or tip of the ear that are less than half the size of normal size kernels.)

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

Step 5. Repeat the procedure for at least four additional sites across the field.

Example: You are evaluating a field with 30‑inch rows. You counted 24 ears (per 17' 5" = row section). Sampling every fifth ear resulted in an average row number of 16 and an average number of kernels per row of 30. The estimated yield for that site in the field would be (24 x 16 x 30) divided by 90, which equals 128 bu/acre.

THE EAR WEIGHT METHOD can only be used after the grain is physiologically mature (black layer), which occurs at about 30‑35% grain moisture. Since this method is based on actual ear weight, it should be somewhat more accurate than the yield component method above. However, there still is a fudge factor in the formula to account for average shellout percentage.

Sample several sites in the field. At each site, measure off a length of row equal to 1/1000th acre. Count the number of harvestable ears in the 1/1000th acre.

Weigh every fifth ear and calculate the average ear weight (pounds) for the site. Hand shell the same ears, mix the grain well, and determine an average percent grain moisture with a portable moisture tester.

Calculate estimated grain yield as follows:

Step A) Multiply ear number by average ear weight.

Step B) Multiply average grain moisture by 1.411.

Step C) Add 46.2 to the result from step B.

Step D) Divide the result from step A by the result from step C.

Step E) Multiply the result from step D by 1,000.

Example: You are evaluating a field with 30‑inch rows. You counted 24 ears (per 17 ft. 5 in. section). Sampling every fifth ear resulted in an average ear weight of 1/2 pound. The average grain moisture was 30 percent. Estimated yield would be [(24 x 0.5) / ((1.411 x 30) + 46.2)] x 1,000, which equals 135 bu/acre.

Because it can be used at a relatively early stage of kernel development, the Yield Component Method may be of greater assistance to farmers trying to make a decision about whether to harvest their corn for grain or silage. Since drought stress conditions in some fields may result in poorly filled small ears, there may be mechanical difficulties with sheller or picker efficiency that need to be considered. When droughts occur, it’s often cheaper to buy corn for grain than to buy hay for roughage (because of likely forage deficits). Therefore, there may be greater benefit in harvesting fields with marginal corn grain yield potential for silage.

Reference

Thomison, P. and A. Geyer. 2007. Abnormal corn ears. Ohio State University Extension. ACE-1. available at https://agcrops.osu.edu/specialists/corn/resources/of-interest/AbnormalCornEarsPoster_000.pdf (URL verified 8/9/10)

Managing Biennial and Perennial Weeds in Wheat Stubble

The late summer and fall following wheat harvest can be an optimum time to apply herbicides for control of biennial and perennial weeds. Perennials can be classified as either warm-season or cool-season for the purposes of determining when to apply herbicides in the fall. Warm-season perennial species are those that die or are severely injured after the first frost in the fall. Examples of warm-season perennials include hemp dogbane, common milkweed, pokeweed, horsenettle, and johnsongrass. Cool-season perennials and biennials will survive several frosts and are typically still green into about early November. Cool-season perennials include quackgrass, curly dock, Canada thistle, and dandelions. Biennials that survive into late fall after their first season of growth include poison hemlock and wild carrot, and these are much more effectively controlled by fall herbicide treatments, compared with spring burndown treatments. 

As a general rule, most effective control will occur when perennials are at least 8 to 15 inches tall at the time of herbicide application. Apply herbicide prior to the onset of plant senescence, or by about mid-bloom for any species that are flowering in the early fall. Fields should not be mowed from this point on, to allow perennials to grow to an appropriate size. For control of warm-season perennials, apply herbicides in mid-September or at least one week before a light frost. For control of cool-season perennials and biennials, apply between mid-October and early November. Control of cool-season perennials can be more effective when a light frost occurs prior to herbicide application. 

We suggest applying a mixture of glyphosate and 2,4-D for most effective control of broadleaf biennial and perennial weeds. Exceptions to this include any field where perennial grasses or Canada thistle are the primary target, since glyphosate alone can adequately control these perennials, and the addition of 2,4-D can reduce the activity of glyphosate on these species. Glyphosate labels contain specific information on the rates required for control of many perennial species, and a quick review of this section of the label can help in decisions on rate. Our general recommendation for a mixed bag of perennial species is to apply the following: glyphosate @ 1.1 to 1.5 lb ae/A plus 2,4-D ester @ 0.5 to 1 lb ai/A. The higher rates can result in more effective control of the harder to control perennial weeds, and also perennial grasses. However, Canada thistle and quackgrass can be effectively controlled by glyphosate applied alone at the rate of 0.75 lbs ae/A, when applied in a spray volume of 10 gpa or less. Include ammonium sulfate at recommended rates. Additional information can be found on glyphosate labels, and in the “Problem Weeds” section of the “Weed Control Guide for Ohio and Indiana”. The bulletin can also be viewed online at http://www.btny.purdue.edu/Pubs/ws/ws-16/

 

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About the C.O.R.N. Newsletter

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.