C.O.R.N. Newsletter 2004-26

Dates Covered: 
August 10, 2004 - August 17, 2004
Editor: 
Harold Watters

Soybean Defoliators

Authors: Ron Hammond, Bruce Eisley

Various insects continue to defoliate soybeans in parts of Ohio, although we should start seeing a decline over the next few weeks. Japanese beetles, with a single generation per year, should continue feeding for a short while and then start to disappear. First generation bean leaf beetles are nearing the end of their feeding cycle, although the second generation that will be feeing on pods will start to emerge near the end of August and September. Mexican bean beetle, although not as widespread in Ohio, are into their second generation of which both larvae and adults feed on leaves. Grasshoppers will continue to feed until plant maturity, although their feeding is generally concentrated on the field edges.

There are two important considerations with all soybean defoliators that growers should keep in mind. The first concern is that many soybean fields in Ohio are in the beginning and full seed growth stages, R5 and R6, respectively. At the end of the R5 stage and into the R6 stage, the defoliation threshold rises to 25%, which is basically a fourth of the leaf area. This is a lot of defoliation, and is seldom reached unless there is a very large insect population or complex of insects present. While the defoliation threshold in late-planted soybeans, still in the R2-R4 growth stages, remains at 15%, early-planted soybeans have had their thresholds increased. The second concern relates to the preharvest interval of insecticides for use against soybean defoliators because some of the insecticides have relatively long preharvest intervals. If any insecticide application is made at this time, growers need to be aware of this interval, which can range from a few days to 45 or 60 days. See http://ohioline.osu.edu/b545/b545_24.html for a list of soybean insecticides and their preharvest intervals.

Soybean Aphid Update

Authors: Ron Hammond, Bruce Eisley

We are still seeing very low populations of soybean aphids in Ohio, as well as in other states throughout the Midwest. We have received a few reports of some fields in Ohio having noticeable numbers, but on visiting those fields, are only seeing an average of 10-30 aphids per plant. Of importance, many of those fields are into late seed fill or full seed, growth stages R5 and R6, respectively. At these later growth stages, it would probably take many more aphids than normal to cause a yield loss. Our current threshold of 250-300 aphids per plant is for use during growth stages R1-early R5. Although we are not sure where the threshold should be on late R5 and R6 soybeans, we do believe that it is much higher. Of importance, we are not aware of any soybean fields in Ohio being anywhere near those levels, let alone being close to the 250-300 aphids per plant threshold for R1-R4 soybeans. Although early-planted soybeans are nearing the end of their growth cycle, we still recommend keeping an eye on late-planted soybeans that are still in R2-R4 growth stages. However, growers should still wait until the threshold of 250-300 aphids is reached before taking action, and make sure that correct identification is made and not confuse potato leafhopper nymphs nor thrips with the aphids (see a previous CORN newsletter http://corn.osu.edu/story.php?setissueID=46&storyID=236 for a discussion of this). Although we still have about 3-4 weeks of watching for aphids, it appears that we might be clear of large-scale aphid problems this year. However, because next year might be a different situation, we recommend growers continue to become more informed about this pest.

Sudden Death Syndrome and Soybean Cyst Nematode

Authors: Anne Dorrance

It may be the effect of having two teenagers in the house now, but I take special delight when I am right about something!! Soybeans with symptoms of sudden death syndrome (SDS) were brought in this week and they had soybean cyst nematode. Ohio continues to have SDS in areas of fields which are wet but also have moderate to very high levels of SCN. Leaf symptoms of SDS start out as small bright yellow spots, which grow together and become tan. The appearance then changes to where the area between the leaf veins is all brown surrounded by bright yellow. SCN can be found on the roots. Dig the plants out of the soil and look for tiny white pearls on the roots. If you hold the roots in the air for a few minutes, the sand grains will dry and you can find the SCN bodies a bit easier because they will still be glistening. Two strategies are needed for SDS, first manage the SCN population by rotating out soybeans and planting non-hosts such as corn or wheat. The second is to improve drainage. The fields with SDS that I have been in tend to be corners or along roadsides or fields where the water is not well drained. Improving the drainage in that location will help. For more information concerning SDS and SCN check the fact sheets at www.oardc.ohio-state.edu/ohiofieldcropdisease .

Calcium and Gypsum, What Does it Do for Your Soil?

Authors: Robert Mullen, Edwin Lentz

Maintaining an optimum calcium (Ca) to magnesium (Mg) ratio for proper nutrition of higher plants was initially introduced in the ‘40s based on research conducted in the Northeastern US. The premise of this research was that maintenance of a certain base saturation and subsequent nutrient ratio would provide adequate nutrition and promote good plant health. Since, multiple studies have been conducted (including research in Ohio) to evaluate the effects of base saturation and varying nutrient ratios on yield potential of several field crops. To date, the research time and again shows that maximum yields are attainable at different base saturation levels and nutrient ratios as long as nutrients are not deficient (above the critical level).

More recently in lab experiments, applications of calcium rich gypsum have been reported to improve water infiltration, reduce surface crusting, and decrease soil erosion. These improvements in soil physical characteristics are due to increased divalent cation concentrations which have been shown to improve soil water holding capacity compared to monovalent cations. Basic cations that have two charges (Ca+2 and Mg+2) contribute to better moisture holding of clays than cations with single charges (K+ and Na+). This is especially true of high clay soils. What is interesting about these studies is that Mg improves soil moisture retention as well as Ca. Thus application of either improves soil moisture absorption compared to K and Na dominated soils. However, at this time, Midwest university research has not shown an increase in crop yields from gypsum applications.

Gypsum application is highly beneficial on sodic soils (soils with high sodium (Na)). Sodic soils are dispersed and inhibit water uptake of growing plants. Calcium applied as gypsum replaces the Na in the system and promotes flocculation (aggregation) of clay particles, increasing moisture absorption and plant available water. Remember, gypsum is not a liming material. In fact, application of gypsum will not alter soil pH at all because it is a neutral salt (actually high pH soils >8.6 will have a decrease in soil pH).

Ohio Wheat Performance Trial: Interpreting the Results for Risk Management

Authors: Patrick Lipps

Agricultural producers are specialists in risk management. Fortunately Ohio wheat growers have several tools available to help make risk management decisions. A highly valued one is the Ohio Wheat Performance Trial, available on the web at the Ohio Ag Crops Network website https://agcrops.osu.edu/ or http://www.oardc.ohio-state.edu/wheat2004/. Paper copies are also available in the county extension offices.

To adequately manage risk a grower must be well informed. Wheat growers are encouraged to study the results of these trials because they provide much more data on the wheat varieties than most other trial reports. In addition to yield results from five locations, other important characteristics of each variety are also presented. Variety characteristics such as test weight, plant height, lodging, heading date and seeds per pound are presented so you can make comparisons among the top yielding varieties. Additionally, this year each variety was evaluated for head scab, powdery mildew and leaf blotch diseases. Grain quality traits (percentage flour yield and flour softness) are also presented for those interested in these factors.

Variety selection is probably the most important pre-planting decision a grower needs to make. Choosing the right variety for your farm can add as much as 8 to 10 bu/A to your overall yield potential. This could be the difference between making money and breaking even (or loosing money) on a wheat crop. If you are planting significant acreage to wheat, always plant several different varieties. Choose all varieties based on yield potential, test weight and standability. Make the selection among different varieties to plant based on relative maturity (heading date) and disease resistance. Choose varieties with different heading dates so that the crop does not flower at the same time. This will lower your risk of the entire crop being hit with head scab. If powdery mildew and/or Stagonospora leaf blotch was significant on your farm then get varieties with better levels of resistance to these diseases. You might even want to try some of the newer varieties with moderate scab resistance.

Ohio wheat producers should choose varieties with resistance (R) or moderate resistance (MR) to powdery mildew because it is the most common disease in wheat fields early. Secondly, look for varieties with moderate resistance to leaf blotch diseases, particularly caused by the fungus Stagonospora nodorum. Stagonospora leaf and glume blotch is very common, particularly in wet, warm seasons. Unfortunately, too many wheat varieties are susceptible to this significant disease. Leaf rust can be common in southwest and northwest Ohio in some years and its occurrence is generally unpredictable. Experience has indicated that leaf rust generally infects fields late enough (watery ripe stage or later) that it causes little yield loss except on the most susceptible varieties. Head scab has cause severe epidemics in Ohio during the past 10 years and traditionally there has been few varieties with usable levels of resistance. We were able to evaluate the scab reaction of varieties at three locations of the Ohio Wheat Performance Test this year. According to this data, there were about 15 varieties that had moderate levels of scab resistance (MR) of the sixty some varieties tested. Most importantly, try to avoid varieties with high susceptibility to head scab.

Bottom line: Get the variety information you need to make good choices before you purchase wheat seed. Choosing disease resistant varieties helps manage risk and could have reduced that 15% yield loss you endured this year.

Warning About Saving Wheat Seed for Planting in the Fall

Authors: Patrick Lipps

We have reports from wheat seed producers in Ohio indicating that there are seed quality issues associated with the wheat seed available for planting this fall. Wet weather during the grain filling period of the crop caused conditions favorable for infection by several seed borne fungi: Fusarium graminearum and Stagonospora nodorum. These fungi are the cause of Fusarium head scab and Stagonospora glume blotch, respectively. Any grain that will be saved for seed will need to be thoroughly cleaned to remove all small, shriveled seed and the seed will need to be stored under dry conditions until planting time to avoid mold and further deterioration of the seed. Air cleaning will not be sufficient to remove all diseased seed, but a gravity table will do a much better job if set to clean out sufficient light weight seed. Several seed processors have reported that they are discarding about 20% of the grain during the cleaning process to improve seed quality. Growers that do not have the facilities to adequately clean seed, store the seed and have it treated with an effective fungicide probably should not save their seed this year.

Not cleaning and treating seed will likely lead to increased disease problems in the next crop. The fungi that cause head scab and Stagonospora glume blotch will remain on the seed during storage and when planted may cause increased problems with seedling stand establishment. Fungi that cause both diseases can kill seedlings under environmental conditions favorable for seedling blight. Additionally, Stagonospora nodorum will produce spores on the young plans in the fall that may contribute to the overall level of Stagonospora leaf blotch next spring. Therefore, all saved seed will need to be treated with as seed treatment that contains fungicides effective against both of these fungi. Dividend XL, Dividend Extreme, Raxil MD, Raxil XT, Raxil-Thiram have excellent activity against Stagonospora on seed and also provide good control of seed borne Fusarium from head scab. If additional protection from Fusarium is needed you can choose to apply LSP Flowable with the other seed treatment product. LSP Flowable is very effective in reducing Fusarium on seed.

Lastly, all seed should be tested for germination before planting. The final germination test should be run on treated seed because treatment will frequently improve germination. It is not wise to plant seed with germination percentages much under 80%. A germination test is an indication of the level of possible problems that may arise from using poor quality seed and it can be reflected in the yield of the crop. Do not take chances with poor seed, the risks are too great and expensive.

Time to Stop Spraying Soybean Herbicides for the Season

There are only 52 days before October 1st, therefore herbicides should no longer be applied to most of the soybeans in Ohio. Only Basagran, Cobra, and glyphosate can be applied to soybeans with fewer than 50 days until harvest. Basagran can be applied 30 days before harvest, Cobra can be applied 45 days before harvest, and glyphosate products can be applied 7 to 14 days before harvest depending upon the product.

Estimating Corn Yields Prior to Harvest

Authors: Peter Thomison

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. The yield component method involves use of a numerical constant for kernel weight that 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.

Calculate estimated grain yield using the Yield Component Method as follows:
Step 1. Count the number of harvestable ears in a length of row equivalent to 1/1000th acre (watch out for plants with more than one ear). 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 (the value of 90 represents the average number of kernels (90,000) in a bushel of corn).
Step 5. Repeat the procedure for at least four additional sites across the field (this will be particularly important in some fields given the likelihood of uneven stands in due to ponding early in the season).
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 using the Ear Weight Method 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 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.

Southwest Ohio Corn Growers & Fayette County Agronomy Field Day

Authors: John Yost

Please mark your calendars for the 2004 Southwest Ohio Corn Growers & Fayette County Agronomy Field Day, which will be held on Wednesday, August 18th at the Fayette County Airport. Admission is FREE!

You can access the informational flyer at: http://fayette.osu.edu/animal/images/SWO.pdf

If you should have any questions, please feel free to contact John at 740-335-1150.

Archive Issue Contributors: 

State Specialists: Pat Lipps and Anne Dorrance (Plant Pathology), Robert Mullen (Soil Fertility), Jeff Stachler (Weed Science), Bruce Eisley and Ron Hammond (Entomology), Peter Thomison (Corn Production) and Ed Lentz (Agronomy). Extension Agents and Associates: Harold Watters (Miami), Alan Sundermeier (Wood), Glen Arnold (Putnam), Roger Bender (Shelby), Steve Foster (Darke), Howard Siegrist (Licking), Greg Labarge (Fulton), Gary Wilson (Hancock) and Dusty Sonnenberg (Henry).

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.