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October 29 to November 12, 2001
C.O.R.N. 2001-36
In This Issue:
A) Lodged Corn: Heavy Rain, Wind, and Stalk Rots
B) Grain "Shrinkage" in Corn
C) More on Fall Applications and Winter Annual Control
D) Phytophthora sojae Race Shifts in Ohio - Biology Strikes
Again
E) Mustang Labeled on Alfalfa & Corn
F) Agronomic Crop Production Workshops - Winter 2002
G) Ohio Forage Production Short Courses
The events that occurred during the entire 2001 growing season have set the stage for the problems of stalk quality and lodging we now see in corn fields. There are vast differences in the level of harvest problems from one region of the state to another and large differences can be seen from one field to the next within a region. These differences can be associated with various management practices including planting date, tillage, drainage, hybrid, and/or nitrogen status of the field. Additional problems included disease (northern corn leaf blight, gray leaf spot), insect (corn borer) and weed infestations. Large variation in yield also relates to some of these differences. Thus, this year has presented a very complex situation making it difficult to make generalizations as to the cause of production problems. Growers will have to look at the situation in each field individually.
It will be difficult to use hybrid trial results to identify consistent hybrid differences for stalk quality due to the considerable variability in stalk lodging within fields where performance tests were performed. Hybrids that withstood lodging problems in past years may have succumb to a combination of stress conditions this year. Hybrids characterized as "stay green" types generally maintain stalk health and integrity better than others, but even these stay green hybrids may be subject to increased stalk rot potential when stresses are severe as they have been in parts of Ohio this past growing season.
Differences in stalk quality and lodging can be traced back to early season stresses placed on the corn crop. Most early planted corn in the state endured a three week cool wet period during which root systems were damaged, and in many cases plants did not fully recover during the rest of the growing season. The protracted period of wet soil conditions also resulted in loss of nitrogen (N) through denitrification and leaching. This loss of N combined with shallow restricted root systems resulted in N deficiencies in many corn fields. Nitrogen deficiencies along with other stress conditions, reduce the photosynthetic capacity of plants and cut the carbohydrate supply needed for grain fill. Inadequate carbohydrates in stressed plants often results in premature senescence and death of pith cells in the stalk and root tissues which predisposes plants to infection by stalk rot fungi.
In the southern parts of the state, above normal rainfall during most of the summer promoted ear and grain production, but the high yields came at a price. Higher kernel numbers per ear put a lot of stress on plants with poor root systems and predisposed corn to anthracnose stalk rot and stalk quality problems as the crop was maturing. In the north, drought conditions in late June and July placed tremendous stress on plants with poor roots and magnified the N deficiencies that were widely evident in many fields in Northwest and Northeast regions of the state. Once growth and development resumed following rain in these areas, grain fill was the number one priority for corn plants. Poor root systems on corn plants in the north and south has led to lodging problems by causing increased stress levels for the plants trying to produce grain. In many cases plants cannibalized tissues in the lower stalks to provide nutrients to fill the grain. It seems that Gibberella stalk rot is now taking over where anthracnose stalk rot left off.
Anthracnose was the main stalk quality issue through the early parts of corn harvest, but the longer plants remain in the field the greater the chances of Gibberella causing rotted stalks and even more lodging. Gibberella stalk rot generally is first detected in lowest portion of the stalks near the soil surface. The fungus rapidly colonizes stalks of dead plants during periods when the stalks are wet and the temperatures are warm. The precipitation and temperatures from about October 10 through October 23 were near ideal for Gibberella colonization of stalks. High winds last week (Oct 23-26) greatly increased the lodging in fields throughout Ohio. About all growers can do now is to prioritize fields at greatest risk to stalk lodging and continue harvesting at as quick a pace as possible to avoid more losses due to lodged corn.
Water removal is by far the major weight loss component during drying. But a second, smaller portion is dry matter or handling loss due to release of oils, mechanical losses from broken kernels, and respiration from the seed.
Calculation of water loss alone is straightforward and does not vary from load to load or chart to chart. But the actual amount of handling loss will depend on the initial physical quality of the corn and the handling processes during drying. This loss is not measured directly by buyers, but is added to water loss using several different methods of estimation. The most common two methods are: 1) use of drying tables which include water shrink plus a constant handling loss (usually 0.5% of the initial grain weight), or 2) a constant shrink factor in which the assumed handling loss varies depending on the initial grain moisture content.
In order to accurately compare custom drying quotes or grain sale alternatives, corn growers must determine the shrinkage costs associated with each and choose the alternative which returns the greatest dry bushels or highest net sale.
For examples of how to do such comparisons (and a more detailed description
of shrinkage calculation differences), see National Corn Handbook Publication
NCH-61, "Calculating Grain Weight Shrinkage in Corn Due to Mechanical Drying."
It's available on-line at http://www.agcom.purdue.edu/AgCom/Pubs/NCH/NCH-61.html
Please contact me (via your local Extension Office) if you would like a hard
copy of this publication.
In our CORN articles this fall, we have discussed strategies for managing winter annual weeds, including fall herbicide applications. We listed the herbicides and herbicide combinations that provided greater than 80% control of both common chickweed and purple deadnettle. Some treatments did not make this list because they were weak on one or both of these weeds. For example, simazine alone provides better then 80% control of chickweed, but does not provide effective control of deadnettle unless mixed with another herbicide. The combination of Sencor/Python provides better than 80% control of deadnettle, but is variable on chickweed. Valor is now labeled for fall application and was included in our research last year. Valor has been variable on deadnettle (excellent at two sites and poor at the third) and not adequate for chickweed at the site where that weed was present. We are conducting field studies again this fall and spring on deadnettle and chickweed, and these treatments may or may not prove to be more consistent with additional testing. What is clear at this point to us is that a number of other treatments, as listed in previous CORN articles, did provide consistent control of both weeds across all of our research sites. We are also conducting research this fall and spring on marestail, which has become extremely problematic in some areas of the state. We know that some marestail populations are resistant to ALS-inhibitors, and products such as Canopy XL, Python, and FirstRate will provide little to no control of these populations. With regard to soybeans, Sencor and Valor are the only other active ingredients available that provide residual control of marestail. Both of these products can be applied in the fall prior to corn or soybeans. Little research-based information is available on the length of residual marestail control for Valor or Sencor, but we should have a better idea of this after the upcoming year's research. The Valor label also claims residual control of dandelion and cressleaf groundsel.
The following are the results of a 2 year study funded by the Ohio Soybean Council, with check-off funding. To begin with, Ohio State has been monitoring P. sojae populations in Ohio for over 40 years. We do this for disease prediction as well as to help companies make decisions on which Rps genes or types of resistance to add to the soybean cultivars slated for sales in Ohio.
We collected soil samples from 86 location in 20 counties. The majority of the counties are located in northwest Ohio in fields with very high clay content, but we added several counties to the south including Brown, Highland, Clinton and Darke. From these soil samples we were able to isolate P. sojae from 82 of the 86 locations. These results indicate that P. sojae is quite prevalent in Ohio fields.
We then took those isolates and determined which resistance gene they could attack (the race or pathotypes). This was done by inoculating a series of soybean lines each with a different single resistance (Rps) gene. The response of the soybean line is dead or alive and this gives a pathotype pattern, ie: which Rps genes are not effective when plants die when inoculated with a particular isolate. A race is a designated code based on the pathotype. For example Race 1 of P. sojae can only kill plants with the Rps 7 gene and Race 25 can kill plants with Rps1a, Rps1b, Rps1c, Rps1k and Rps7 genes. There are 13 different Rps genes known, but only Rps1a, Rps1b, Rps1c, Rps1k and Rps3a are available in commercial cultivars.
From the 82 fields that we recovered P. sojae there was a tremendous amount of variability with regards to which Rps genes were no longer effective. In other words, we detected a large number of races. If we look at this over all of the locations the results are as follows:
Rps gene Percentage of locations where differential was killed
Isolates could kill plants with this Rps gene
Rps1a 95%
Rps1b 65%
Rps1c 73%
Rps1k 78%
Rps3a 51%
Rps6 52%
These results indicate that P. sojae populations in Ohio have adapted to many of the commercial Rps genes that are currently available in soybean cultivars. How can producers benefit. We fully expect to see more impact on our soybean cultivars to P. sojae in the future. The last widespread losses of P. sojae were in the late 70's. Growers/Crop consultants and field scouts should begin to familiarize themselves with the symptoms caused by P. sojae. We did not see a pattern, where every field in a county had the same races. We think at this time period, the P. sojae populations are in mid-change - as we continue to plant beans with a specific gene (Rps1k for example), the pathogen populations will continue to climb.
The best means to alleviate yield impacts by P. sojae is to select varieties with an Rps gene but also to include the highest levels of partial resistance. When you sit down with your seed dealer this fall/winter ask your self these questions:
Have I had replant problems?
Have you seen Phytophthora stem rot develop later in the year?
Is your field well drained and the tiles well spaced (<30' on heavy clay
soils)?
Beans planted in a field more than 3 out of the past 5 years?
Yes to any of these questions indicate that this field is at risk for losing yield to P. sojae. If an Rps gene is effective against a population there will be very little impact. However, if it's not effective, losses reaching 80 to 100% have been documented previously. Partial resistance to P. sojae combined with single gene resistance will prevent major losses. Remember to check the scores of different cultivars, each company scores partial resistance differently. The last widespread losses of P. sojae were in the late 70's. Keep good records of the resistance package that comes with your seed and check it throughout the season to be sure that it is giving the protection that you need. Keep records of varieties, the Rps genes and level of partial resistance over the years so this information can be used in the future to help manage this disease.
FMC Corporation has informed us that Mustang, Zeta-cypermethrin, has received label for use on alfalfa and corn along with several other crops. Mustang is labeled on alfalfa for all of our common alfalfa insect problems including alfalfa weevil, potato leafhopper, meadow spittlebug and aphids. It has a 3 day waiting period before harvest on alfalfa. Mustang is labeled on corn for all of the common pests including cutworms, flea beetles, armyworms and others. Check the labeled for all of the pests labeled on corn. Mustang is a Restricted Use Pesticide with a Warning on thelabel.
Soil Fertility Workshops
Corn Production and Management Workshops
Soybean Production and Technology Workshops
Wheat Production and Management Workshops
All of these workshops are open to farmers and agribusiness personnel. Certified Crop Advisor credits (4-5 hours) and Commercial and Private Pesticide Applicator credits (1-2 hours) will be given to participants. Registration materials for each set of workshops will be available around December 1st.
For more information on these workshops including resource speakers and registration
information see the following website:
http://www.ag.ohio-state.edu/~corn/programs.html
Northeast Ohio
December 3 and 6, 2001
First United Methodist Church244 South Broadway
Salem, OH 44460
Host: Ernie Oelker (330) 424-7291
Southwest Ohio
January 22 and 24, 2002
Appalachian Gateway Center
Southern States Community College - South Campus
12681 US Route 62
Sardinia, OH 45171
Host: David Dugan (937) 378-6716
To register, contact the above individuals, or contact:
Mark Sulc(614) 292-9084
sulc.2@osu.edu
The curriculum will cover all aspects of forages --from production to storage to utilization -- but the emphasis will be on management and how to produce high-quality stored forages more efficiently and more effectively. A team of specialists will provide classroom instruction plus hands-on activities. Each participant will receive a resource notebook full of valuable references, bulletins, fact sheets and articles.
A total of 10 continuing education credits for Certified Crop Advisors (CCA) will be offered for the courses. The breakdown of the credits is: 1 for nutrient management, 7 for crop management, and 2 for pest management.
Each site is limited to 30 participants, and the $60 pre-registration is required. Get registration forms from county Extension offices in Ohio. Registration materials will soon be posted on the web at: http://forages.osu.edu, and click on "Events" to find the Forage Production Short Courses listed and a link to course registration.
Surveys of last year's course participants showed that they felt the course
was very worthwhile. Most said they would be making changes on their farms or
in their recommendations to farmers based on what they learned during the course.
The reference manual was especially popular with the participants. Another key
benefit stated by participants was the opportunity to meet other forage producers
and exchange ideas, and several even forged potential business relationships.
All said they would recommend it to a friend.
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.
State Specialists: Pat Lipps, Anne Dorrance and Dennis Mills (Plant Pathology), Bruce Eisley (Entomology), Mark Loux and Jeff Stachler (Weed Science), Mark Sulc (Forages), Peter Thomison (Corn Production). Extension Agents: Roger Bender (Shelby), Gary Wilson (Hancock), Dennis Baker (Darke), Greg LaBarge (Fulton), David Jones (Allen), Glen Arnold (Putnam), Steve Prochaska (Crawford), Barry Ward (Champaign)Editor: Barry Ward 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.
TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868
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