CORN
Crop Observation and Recommendation Network

September 18 to September 24, 2000
C.O.R.N. 2000-31

In This Issue:

A) Corn Harvest Losses and Grain Drydown Rates.
B) Plant Disease Resistance Genes, How to Utilize Them
C) Fees For Soybean Cyst Nematode Testing For 2000-2001
D) Visit the OSU Agronomic Crops Team at the Farm Science Review and Receive a Free Gift

A) Corn Harvest Losses and Grain Drydown Rates - Peter Thomison CORN Questions

Corn growers may encounter slower than normal drying rates this fall due to relatively cool weather conditions and late crop development in parts of the state, especially the northeast. The ideal kernel moisture level to harvest corn at for dry grain storage is considered 25%. The yield potential of corn fields in localized areas could drop considerably if harvesting is delayed much beyond maturity because of stalk lodging associated with poor stalk quality. Root lodging caused by wind storms earlier this year may also slow harvest and contribute to yield losses.

The loss of one "normal" sized ear per 100 feet of row translates into a loss of more than one bushel/acre. In fact, an average harvest loss of 2 kernels per square foot is about 1 bu/acre! According to an OSU agriculture engineering study, most harvest losses occur at the gathering unit with 80% of the machine loss caused by corn never getting into the combine.

Corn will normally dry approximately 3/4 to 1% per day during favorable drying weather (sunny and breezy) during the early warmer part of the harvest season from midSeptember through late September (probably a week to 10 days earlier, respectively, for southern and northern Ohio). By early to midOctober, drydown rates will usually drop to ½ to 3/4% per day. By late October to early November, field drydown rates will usually drop to 1/4 to 1/2% per day and by mid November, probably 0 1/4% per day. By late November, drying rates will be negligible.

Estimating drydown rates can also be considered in terms of Growing Degree Days (GDDs). Generally, it takes 30 GDDs to lower grain moisture each point from 30% down to 25%. Drying from 25 to 20 percent requires about 45 GDDs per point of moisture. In September we generally average 1015 GDDs per day. In October (as things cool down) the rate drops to 510 GDDs per day. However, note that the above estimates are based on generalizations, and it is likely that some hybrids vary considerably from this pattern of drydown.

We conducted evaluations of corn drydown at the OSUOARDC Western Branch Research Farm, near S. Charleston, OH in 1991 and 1992. In 1991, under warm, dry fall conditions, grain moisture loss per day ranged from 0.76 to 0.92%. Whereas under cool, wet fall conditions in 1992, grain moisture loss per day ranged from 0.32 to 0.35%. Grain moisture losses based on GDD ranged from 2429 GDD/percent moisture (i.e., a loss of one percentage point of grain moisture per 2429 GDD) in 1991, whereas moisture loss ranged from 2022 GDD in 1992. The number of GDDs required to reduce grain moisture was lower in 1992 than 1991.

B) Plant Disease Resistance Genes, How to Utilize Them - Anne Dorrance, Mac Riedel and Pat Lipps CORN Questions

We manage many of our field crop diseases by planting varieties which have resistance genes to certain plant pathogens. Resistance in field crops can be many types. Some types of resistance provide complete control and little to no disease develops; or other types of resistance slow the rate of disease development and subsequently limit yield losses. Plant pathogens are biological organisms that change and adapt to many situations. It takes many years to identify sources of resistance and develop varieties. In some cases, the are few lines that can be used as sources or resistance. Such is the case for soybean cyst nematode. Very few sources of resistance for SCN have been identified and most of these have poor agronomic traits. This requires many years to develop varieties which have adequate levels of resistance and also have many good agronomic traits such as yield. To date in Ohio, only two sources of resistance are available in soybean varieties which are acceptable to be produced in this region: PI88788 and Peking.

Resistance to SCN is measured in soybean varieties by comparing the reproduction levels of the females (how many eggs are produced) on a resistant line to a susceptible line. In some resistant reactions the females may have fewer feeding sites, she may produce only a few eggs where in a susceptible line there will be more feeding sites and she will produce numerous eggs. We also know that within any given field the SCN populations are variable and there are individuals that reproduce extremely well on SCN resistant lines.

We manage SCN populations by starving them when we plant non-host crops such as corn and wheat and keep our weeds under control in the rotation cycle. It is CRITICAL to the success of this program that we do not over utilize our SCN resistant soybean varieties. When SCN resistant beans are planted into fields with HIGH cyst or egg counts (3 or more cysts or 2,000 or more eggs) those individuals which can reproduce well on that resistant variety will increase in number. The counts will begin to appear like those with a highly susceptible soybean variety and the yields will begin to plummet. Reports of 5 to 15 bushels per acre are not uncommon for this situation.

The bottom line: NEVER EVER plant SCN resistant varieties in fields with cyst counts greater than 3 and egg counts greater than 2,000. The magic bullet for SCN is ROTATION. We are fully aware of the economics that producers face in agronomic crop production, but the long term impact of high SCN populations and low yields down the road are a greater economic risk. In addition, every time you move equipment in and out of these fields you will be moving these cysts which can favor resistant lines into more fields thereby increasing your problems.

C) Fees For Soybean Cyst Nematode Testing For 2000-2001 - Mac Riedel, Nancy Taylor and Anne Dorrance CORN Questions

Since the autumn of 1998, 7,674 soil samples have been processed at Ohio State University for growers and consultants interested in soybean cyst nematode (SCN) detection, in a program funded by the Ohio Soybean Council using checkoff dollars. Of these samples, 3,781 or 49% have contained detectable levels of SCN eggs. Populations of the nematode are known to exist in 61 counties in Ohio.

Fields should be sampled in the fall following harvest. How often to sample fields will depend on several factors 1) is SCN present and 2) rotation schedule.

If you are in a 3year rotation and populations are low or zero, probably once every 10 years prior to a soybean crop will be sufficient. If the field is in 2year rotation, and populations are low or zero then every five years prior to a soybean crop. If populations were high then sample before each soybean crop to ensure that populations are dropping sufficiently during the years in corn and SCN resistant soybeans. If you are not rotating and relying on SCN resistant beans, which is not advised, then we highly recommend that you sample every fall. SCN populations do develop a healthy appetite for SCN resistant beans and this will need to be monitored quite closely. The end result is a field with extremely high populations in which the beans are severely stunted and produce less than 10 bushels/acre.

The main objective of the sampling program sponsored by the Ohio Soybean Council, to raise awareness of soybean cyst nematode in Ohio soybean fields, has been achieved. The SCN program now moves to the next phase in which soil sampling for SCN before planting soybeans becomes a part of production planning, along with routine testing for fertility needs. Therefore the charges for SCN testing have been reinstated at the C. Wayne Ellett Plant and Pest Diagnostic Clinic. The funds received from the Ohio Soybean Council from the checkoff have been essential in identifying the problem in Ohio. SCN will not disappear but with a good rotation schedule, use of SCN resistant varieties in SCN fields and soil sampling to monitor SCN populations should minimize yield losses to this Soybean pathogen.

Beginning October 1, 2000, for a single shipment of soil samples from an individual farm the fee will be: $15.00 for the first soil sample, $10.00 for each additional soil sample in the shipment.

Sampling Instructions:

1. Use a 1inch diameter soil probe to collect soil samples (68 inches in depth)
2. Following a zigzag pattern, collect 1020 soil cores per 1020 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.
7. Samples may be sent to: C. Wayne Ellett Plant and Pest Diagnostic Clinic 110 Kottman Hall, 2021 Coffey Road Ohio State University Columbus, OH 432101087

D) Visit the OSU Agronomic Crops Team at the Farm Science Review and Receive a Free Gift CORN Questions

The first 35 visitors, each day, to the Ohio State University Agronomic Crops Team tent at the Farm Science Review who bring a copy of this week’s C.O.R.N. Newsletter will receive a copy of the popular OSU Extension Bulletin 827 “Corn, Soybean, Wheat and Alfalfa Field Guide” as a free gift. The tent will be located Northeast of the Bailey Building on Farm Avenue, adjacent to the Utzinger Garden. Agronomic Crops Team members will be on hand to answer questions and poster presentations from various team members will be on display.

Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.

Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/

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.

Editor: Clark Hutson         Web Editor: Tom Rosati

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

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