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For Week of August 24 - 30, 1998
C.O.R.N. 98-24
In This Issue:
A) Corn Leaf Diseases, Stalk Rots and Lodging
B) Estimating Grain Yields in Corn Prior to Harvest
C) Harvest Corn Silage at Proper Dry Matter Content
D) Stored Grain Pest Management
E) Spider Mites on Soybeans
F) Modified Relay Intercropping Update
In most areas of the state we can find a number of different diseases affecting the upper leaves of corn plants. The most common diseases are Stewart's bacterial leaf blight and gray leaf spot, but common rust and northern leaf spot (Carbonum leaf spot) are also present. The good news is that the corn has advanced rapidly through its growth stages and many fields are already in the dent stage. Yield losses from diseases affecting the leaves after this stage will be minimal. However, you can expect the diseases to increase rapidly from now until the plants die, because the plant loses its ability to restrict lesion development and there are a lot of spores being produced on leaf lesions capable of causing new lesions.
At this point we are more concerned with the potential for stalk rot diseases and lodging than we are with the development of additional of leaf disease. Fields with considerable leaf damage from diseases are high risk for stalk rots. Past experience has also indicated that years with adequate to surplus moisture early in the season followed by late season moisture stress are most prone to stalk rots and lodging. There are several different stalk rots, but anthracnose and Gibberella stalk rot are the most common and severe. At this time you can watch for premature death of stalks in the field. When walking through fields examine the stalks of the plants. Those that are beginning to turn a pale green to yellow color are most likely affected by stalk rots, and will have the greatest potential for lodging prior to harvest. As harvest season approaches growers are encouraged to survey their fields to determine those with the greatest level of stalk rots and to harvest them first before lodging occurs. We will be providing more information on stalk rots and the risks this year as the season progresses
Two procedures which 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. 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. If stress conditions, such as drought, have resulted in poorly filled small ears, there may be mechanical difficulties with sheller or picker efficiency which need to be considered. Since it will probably be cheaper to buy corn for grain than to buy hay for roughage (because of the likely forage deficit), there will be greater benefit in harvesting fields with marginal corn grain yield potential for silage.
Much of the corn planted in April through mid May is rapidly maturing due to the warm, dry weather conditions we've experienced in recent weeks. Corn growers planning to ensile corn should be monitoring corn fields closely because their corn may be near or at the optimal stage for silage harvest.
Determining the proper time to harvest corn for silage is critical because whole plant dry matter (DM) content varies with maturity and it influences fermentation. Ensiling corn silage that is too wet produces poor fermentation, seepage losses, and lowered animal intake. Ensiling excessively dry corn increases the risk of heat damage and molding. Corn silage preserved between 30 and 40% DM generally provides good fermentation and animal performance, but different storage structures require different DM concentrations for optimal fermentation. Table 1 shows the recommended target DM content for corn silage in different types of structures:
Table 1. Recommended Dry Matter Content for Corn Silage Stored in Different Structures
Upright, Top Unloading
30 - 40% DM
Upright, Bottom Unloading 40 - 45% DM
Horizontal
30 - 35% DM
The recommended DM content for upright, bottom unloading silos is higher to ensure easier unloading. Horizontal silos require a lower DM content (higher moisture content) to ensure adequate packing to eliminate oxygen and prevent heating.
Observing the development of the corn kernel milkline has been suggested as an easy way to estimate when corn is at the proper dry matter content for ensiling. Generally, recommendations have been to harvest corn for silage when the milkline is 1/2 to 2/3 of the way down the kernel. However, our research has indicated that there is a lot of variability in the relationship between the kernel milkline and whole plant DM content. The milkline is not a very accurate or reliable guide to gauge whole plant DM content. Hybrid, planting date, and growing season can affect the relationship between kernel milkline position and whole plant DM content. However, the appearance of the milkline in the upper 1/4 of the kernel indicates that the crop is very near the optimal time to harvest. A sample should be taken at this time and DM content determined with a commercial forage moisture tester or microwave oven.
Using a commercial forage moisture tester or microwave oven to determine the DM content is the best way to accurately determine the optimal time to harvest corn silage according to the storage structure to be used. And keep in mind that waiting until blacklayer will almost always result in corn being too dry for proper packing and fermentation, especially in horizontal and upright, top unloading silos.
A limited sampling of research plots on 8-20-98 in central and southwestern Ohio indicated that a number of early to mid maturing hybrids were at the full dent stage of kernel development, with some corn as far along as 1/4 to 1/2 milkline.
It has been a hot summer, corn is maturing rapidly, and harvest will likely be earlier than normal. Thus, it is time to begin preparing storage bins for the fall harvest. The first step of the storage preparation process generally includes cleaning out the grain from the past season so that one begins with a clean and empty bin. Rule number one for on-farm grain management is never stored new grain on top of old grain. It is important to eliminate all possible sources of infestation that may have developed during the past year, thus it is important to start the new storage season with a clean bin to which an empty bin treatment has been applied to knock out any insect pests that may remain in the bin.
At this time of the year, when old grain must be moved out, infestations are often discovered. Given the above normal temperatures this summer, insect pests in grain may more abundant. Moisture conditions have varied from one region to another, but region having high moisture conditions may also expect above normal pest activity in stored grain - especially the fungus feeding insects.
If an insect pest infestation is discovered at this point in time, the problems will likely have to be eliminated before the grain can be sold. There are various options for eliminating insects from stored corn which include fumigation, application of a chemical grain protectant, and physical cleaning. However, the option selected will depend on the identity of the storage pest and on the conditions that a buyer will accept in regard to chemical treatments.
If the pest problem is proven to be grain weevils, which internally infest the grain kernals, then fumigation with one of the phosphine gas fumigants is required. However, one should recognize that most insect infestations in stored corn are some pest other than weevil and can be controlled by application of a chemical protectant (Actellic or malathion) or by thorough cleaning process. If a fumigation or chemical protectant treatment is under consideration, it is important to determine what a buyer will or will not accept. These limitations are especially applicable to cases of corn food grains.
Given the hot and some cases dry conditions this summer, infestations of spider mites on soybeans may be detected. The two spotted spider mite thrives in hot weather and plant hosts under draught stress. Late summer infestations of soybeans will likely to limited to the field perimeter or exceptionally dry spots in a field. If the current weather conditions shifts to cooler temperatures associated with some favorable wet conditions, spider mite activity should decline rapidly.
Modified Relay Intercropping (MRI) is the planting of soybeans into standing wheat. Soybeans are generally sown with a drill or tool bar planter, into wheat in 10 to 15 inch rows. Soybeans are normally planted into the wheat from 15-30 days prior to harvest. Thus, an MRI system adds 14-25 days to the soybean growing season when compared to soybeans planted in a double crop system. The wheat plant, by virtue of its adaptability, is able to tolerate slightly wider row spacing and/or the stress of soybean planting with minimal damage.
Sunlight is the energy source necessary for wheat and soybean production. As such, capturing and utilizing as much sunlight as possible, is the primary goal of this and other cropping systems. Light or the lack of it, has a profound effect on the growth of intercropped soybeans. Soybeans planted too early into well-tillered wheat often will become very tall and spindly and result in weak plants that do not grow well. In the MRI system, soybeans planted about 15-25 days prior to wheat harvest have provided the most consistent yields. Theoretically, earlier planted soybeans should yield better, however as was mentioned above, competition with wheat often produces a poor quality soybean plant, or if soybean growth is vigorous, wheat growth is diminished. Therefore, MRI attempts to plant the soybeans into wheat that will soon ripen and allow more light onto the developing soybean plant. The goal in MRI is to balance wheat and soybean plant growth needs and thus maximize yields.
Soybean and wheat yield results over three years in Crawford county replicated plots have been favorable. Wheat has averaged 68 bushels per acre (does not include 1998)and soybeans 32 bushels per acre. This year, wheat averaged 81 bushels per acre in the MRI plots. Soybeans presently also have excellent yield potential.
A tour of four area farms with different MRI systems is scheduled for Wednesday August 26, 1998, from 10:00 a.m. to 3:00 p.m. The tour will begin at the Ohio State University Extension Unger Farm located on Nevada Road .25 mile west of Bucyrus. Tour highlights will include the following:
- Different Wheat/Soybean Row Spacings in MRI Systems
- Wheat Varieties (White and Red) Used in MRI Systems
- Soybean Varieties (Roundup Ready and Conventional) Used in MRI Systems
- Fertility (Nitrogen) Programs in MRI
- Weed Control Programs in MRI
- Interseeding Dates in MRI
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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.
STATE SPECIALISTS: Pat Lipps & Anne Dorrance (Plant Pathology), Hal Willson (Entomology), Peter Thomison (Corn Production), Jeff Stachler (Weed Science) EXTENSION AGENTS: Roger Bender (Shelby), Larry Lotz (Fayette), Clark Hutson (Seneca), Barry Ward (Marion), Gary Wilson (Hancock) and Steve Prochaska (Crawford). Editor: Clark Hutson
Editor: Clark Hutson Web Editor: David Etzkorn
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