C.O.R.N. Newsletter 2006-26

Dates Covered: 
August 14, 2006 - August 22, 2006
Editor: 
Harold Watters

More Reports of SDS, Brown stem rot and Phytophthora

Authors: Anne Dorrance

Late season diseases continue to make their appearance as soybeans across the state hit the R6 growth stage. I received the first sample of brown stem rot last week. The lower stem had a greasy appearance and the pith was the typical chocolate brown color. This was collected from a field that also had plants with the beautiful blue-green colored spores of SDS on the roots. We’ve found this in other fields as well and in fact I have isolated both pathogens from the same plant. When SDS is severe, high level of disease severity, Soybean cyst nematode is also present. Dr. Andreas Westphal at Purdue has just published a very nice study, where they examined the interaction of SCN and SDS and found that SDS disease severity was higher in the presence of SCN. These two pathogens work together in a complex to reduce yields.

The next question is how to manage these problems, especially when they only occur in wet years. First, determine which of these pathogens is causing the most damage. There are resistant varieties available for SDS, SCN, White mold and brown stem rot. With brown stem rot, there is also a pH effect. Dr. Craig Grau at Univ of Wisconsin has reported that when soil pH levels are close to 6.0, severity of BSR foliar symptoms increases.
1. Choose varieties with resistance to plant diseases that predominate in your fields.
2. Maintain good soil fertility and optimum pH for soybean growth and development.
3. Improve drainage, many of these infect plants through the roots and require high levels of soil moisture.
4. Tillage – BSR and Diaporthe stem canker survive on plant residues left on the soil surface. Are your disease levels reaching a point where it is time to look at this disease management practice?
5. Rotate-Rotate-Rotate. The effects of rotation on SCN have been very well documented. When wheat or corn is planted in fields, the SCN levels drop by half.

Soybean cyst nematode (SCN)

Authors: Anne Dorrance, Nancy Taylor, Dennis Mills

Soybean growers in Ohio may be unknowingly losing profits from their soybean crop. The soybean cyst nematode is a soil dwelling organism that can cause yield loss before plant symptoms are obvious.
Analysis of soil samples for SCN submitted by Ohio growers represents less than 3% of the cropland acres and indicates that about 8% have very high levels of SCN (more than 5,000 eggs/200 cc), 6% have moderate levels (2000-5000 eggs), 18% have low levels (200 - 2000 eggs) and 68% have none to trace levels (0 to 200 eggs). Soybean cyst nematode has become an increasingly serious problem in Ohio because more and more fields are being planted to soybeans for multiple years and the nematode has been introduced into fields by machinery. In Ohio, in most years it is difficult to observe any symptoms on affected plants other than decreased yields. When nematode populations are excessively high, or during years with drought, symptoms can include stunting and yellowing.

Recently many reports of Sudden Death Syndrome (SDS) symptoms have been received. The association with SCN is not clear cut but several studies indicate that SCN presence can increase the foliar symptoms of SDS. The fungus has also been shown to overwinter in cysts, thus increasing its survival ability from season to season.

The best way to begin managing SCN is to know which fields have nematodes and how many nematodes are present. Fall is the best time to sample fields for soybean cyst nematodes, when the nematodes have finished producing eggs. Sampling in the fall will give an estimation of the population level on which to base management decisions for planting next spring. Soil samples can be sent to some private labs or to The Ohio State University, C. Wayne Ellett Plant and Pest Diagnostic Clinic. Fees for SCN testing at OSU will be: $15 per soil sample.

C. Wayne Ellett Plant and Pest Diagnostic Clinic
110 Kottman Hall
2021 Coffey Road
Ohio State University
Columbus, OH 43210-1087
614-292-5006
http://ppdc.osu.edu

SCN Soil Sampling Instructions:
1. Use a 1-inch diameter soil probe to collect soil samples (6-8 inches in depth)
2. Following a zig-zag pattern, collect 10-20 soil cores per 10-20 acres
3. Collect cores from areas of similar soil type and crop history
4. Dump cores from each 10 to 20 acre area into a bucket or tub and mix thoroughly
5. Place 1 pint (2 cups) of mixed soil in a soil sample bag or plastic zippered bag and label with a permanent marker
6. Store sample in cool, dark place until shipped to a lab doing SCN analysis.

At trace population levels ranging from 40-200 eggs per 250 cc of soil, some yield loss may be detected when susceptible varieties are grown. If low populations are detected, ranging from 200-2000 eggs, it is recommended to plant a SCN resistant variety, but some yield loss may occur. Under moderate levels of 2000-5000 eggs of soil it is recommended to rotate to a non-host crop like corn, wheat or alfalfa next year and return with a cyst nematode resistant soybean variety the next time soybeans are planted in the field. When high levels of nematodes are encountered, such as 5000 or more eggs, the field should be rotated to a non-host crop for 2-3 years then the field should be resampled before planting a nematode resistant variety to ensure the nematode population has declined enough to successfully plant soybeans again.

Soybean Pod Feeding

Authors: Ron Hammond, Bruce Eisley

With the growing season slowly coming to an end, we should not forget that there is one last insect concern on the immediate horizon for soybean growers. Growers need to remember that grasshoppers and second generation bean leaf beetle adults will become a concern from now until harvest while feeding on pods. Both can cause significant yield loss as well as opening up of the pods to entrance for secondary pathogens. This information should be of particularly importance to those growing food grade soybeans where seed quality is an issue. Although the following information is more for the bean leaf beetle, much of it also pertains to pod feeding by grasshoppers.

When pod injury occurs on 10-15% of pods, seed injury will become evident and yield losses are possible. If the pod injury occurs during periods of wet conditions, this may enable infection by seed diseases; the development of moldy bean seeds may then lead to a loss in seed quality. The assessment of a field infestation depends on (1) determination of the current level of pod injury, (2) the abundance of adult BLB activity using a sweep net, (3) consideration of weather factors that may enable infection of the damaged pods by disease agents, and (4) the amount of time remaining before total leaf drop and dispersal of a BLB population from the field. In terms of this last point, many early-planted fields are entering the full seed stage, and should be maturing in the next few weeks. Although growers should continue to monitor these fields, these soybeans might mature before much pod feeding occurs. Later planted fields, however, will stay green with succulent pods well into September, and thus, growers are advised to pay close attention to their late maturing fields. Hopefully growers have sampled their fields in late July or early August to determine fields already with a large population of bean leaf beetles. The potential for significant pod feeding will be high assuming the fields stay green well into September.

Growers should continue to sample their fields weekly for the remainder of the summer. The percentage pod injury should be determined by randomly counting the total number of pods and those with feeding injury on about twenty plants (see http://ohioline.osu.edu/icm-fact/images/55.html). Adult BLB population should be estimated by taking 10 sweeps with a sweep net at three to four locations in a field.

Rescue treatment to prevent excessive development of seed damage is warranted when pod injury exceeds 10%, fresh feeding scars predominate, and adult BLB are still present and actively feeding (or as it pertains to grasshoppers). Less than two BLB per sweep (20 per 10 sweep sample) are unlikely to cause significant injury. Three to five BLB per sweep (30 to 50 per 10 sweep sample) indicates a potential problem possibly warranting rescue treatment. More than five BLB per sweep (50 per 10 sweep sample) may result in significant injury especially if two or more weeks remain until leaf drop. When the foliage dries and drops, beetles exit the field. Thus, the time remaining for BLB feeding is a key factor in the occurrence of pod injury. Growers also should be aware of the harvest interval with the insecticide that is used for BLB control. Many of the materials have waiting periods of between 21 and 30 days, which begin to limit their use at this time.

Corn Rootworm Problems in First Year Corn: Another Possibility

Authors: Ron Hammond, Bruce Eisley

Although most first year corn rootworm problems are associated with the western corn rootworm variant (only a concern in western Ohio), there is another possibility that we have known about for a long time which might again become a bigger concern in the future. Regular adult western corn rootworms (not the variant) often come into soybean fields to feed on volunteer corn and escaped weeds, which can often lead to significant root feeding the following year if there is a large amount of these present in the soybean field. With the advent of Roundup Ready corn followed by Roundup Ready soybeans, we are seeing an increase in the amount of volunteer corn in some soybean fields along with possible resistant weeds such as ragweed, giant ragweed, and foxtail. The potential exists that this increase in either volunteer corn or weeds might boost the amount of rootworm feeding in first year corn. Thus, when evaluating soybean fields for the presence of adult western corn rootworms and herbicide efficacy, growers should pay attention especially to the amount of volunteer corn in fields with large amounts of volunteer corn (>4000 plants per acre) and heavy numbers of adult beetles, growers should consider the possibility of rootworm problems the following year. Also, when evaluating root injury in first year corn, growers should consider the infestation of volunteer corn and weeds the previous year as a possible reason the for rootworm injury. We will keep watch on this situation over the coming years.

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.

Nitrogen Management Workshop and BMP Challenge Aug 24th

Authors: Harold Watters

Sponsored by the OSU Extension Champaign County and the American Farmland Trust – Best Management Practices Program.

August 24, 2006 9:30 AM to 1:00 PM, includes lunch. To be held in the Champaign County Community Center Auditorium, 1512 South US 68, Urbana OH 43078

Agenda
* 9:30AM Welcome
* 9:45 Brian Brandt will discuss American Farmland Trust and it’s association with the Best Management Practices risk reduction program.
* 10:00 Harold Watters will discuss Nitrogen Management programs locally and some history of the Champaign County program.
* 10:45 Robert Mullen, Ohio State University Soil Fertility specialist will discuss Nitrogen management in Ohio.
* 11:30 Jon Rausch will discuss Manure as an in-crop nitrogen source.
* 12:15PM Lunch

We’ll meet in the auditorium of the Champaign County Community Center at 1512 South US 68, Urbana OH 43078. Please call the Champaign County OSU Extension office to register - 937 484-1526. If you have any questions about the program you may contact Harold Watters (watters.35@osu.edu) at the Champaign County Extension office.

Lunch for those who pre-register by August 21 is free. Producers from Champaign County and surrounding areas are invited to attend.

Robert Mullen is still new to most Ohio producers and has a great background in nitrogen management. He has started a lot of work in the short time he has been here, and has industry experience with sensor technology for managing crops. We’ll also discus how you can take the BMP Challenge and the history of N rate work and yield in the Champaign County area. If you have manures, Jon will discuss how to top-dress or side-dress this valuable N source.

Archive Issue Contributors: 

State Specialists: Ann Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Jeff Stachler (Weed Science), Ron Hammond and Bruce Eisley (Entomology), Robert Mullen (Soil Fertility) and Peter Thomison (Corn Production). Extension Agents: Howard Siegrist (Licking), Harold Watters (Champaign), Glen Arnold (Putnam), Roger Bender (Shelby), Steve Foster (Darke), Steve Prochaska (Crawford), Steve Bartels (Butler), Greg LaBarge (Fulton), Mike Gastier (Huron), Jonah Johnson (Clark), Bruce Clevenger (Defiance), and Keith Diedrick (Wayne).

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.