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For Week of April 20-26, 1998
C.O.R.N. 98-6
In This Issue:
A) Wheat Growth, Disease and Fungicides
B) Soybean Tolerance to Authority Products
C) Early Weed Emergence and Herbicide Programs
D) Nitrogen Management
E) Cerone Application to Wheat
F) Adjust Planting Depth to Optimize Corn Emergence and
Performance
G) Black Cutworm and Common Armyworm Moth Collections
H) Upcoming Field Days at the Fayette County Farm, Washington
Court House, Ohio
Cooler temperatures over the past week have slowed the development of the wheat crop down a bit. We are only about 1 to 2 weeks ahead of schedule throughout the state. Wheat growth stages in Ohio range from flag leaf emergence (growth stage 8) in the southern part of the state to fields in first node (growth stage 6) to second node stage (growth stage 7).
Overall disease level in Ohio is still quite low. Cold night temperatures have probably limited the development of powdery mildew and Septoria throughout the state. We have seen Septoria leaf blotch on susceptible varieties in different locations throughout the state, but cold temperatures are limiting its spread. We visited several fields in southern Ohio last week and found heavy powdery mildew on some very susceptible varieties, but the more resistant varieties had little to no disease. It appears that the level of mildew is very dependent on the variety planted. We suggest that fields of the following varieties be scouted as at or before flag leaf emergence for evidence of powdery mildew: Pontiac, Cardinal, Clark, Dynasty, Grant, Patterson, Podach, Kingston, SR205, 2510, RS927, SG1550, TS4020 and W9140. In most cases the development of the disease has not progressed to the level where a fungicide application should be made. Fields should be scouted just prior to flag leaf emergence to determine if the upper leaves are in danger of infection. It is important to note that the disease is present in the field so these fields can be scouted at a later date, if necessary.
The economics of using a fungicide are most favorable when controlling disease on a susceptible variety in fields with a high yield potential (70-100 bu/A). Costs for a fungicide plus application are around $14-17/A. Scout fields by randomly selecting 30 or more tillers throughout the field. There are 4 main leaves on each tiller of most modern varieties. Examine each leaf on each tiller and assess disease from the top leaf downward on the stem. A fungicide application is most beneficial when the top two leaves (flag leaf and the one below it) are in danger of becoming infected before flowering. Apply fungicide to susceptible or moderately susceptible varieties when disease lesions are just being detected on the second leaf (1% leaf area affected) at growth stages from flag leaf emergence through heading. Tilt can be applied up to flag leaf emergence (growth stage 8) whereas other materials may be applied later, but before 35 days of harvest. Fungicides should be applied in 20 gal water/A with ground equipment or in 5 gal water/A by airplane. This amount of water must be applied with the fungicide to ensure good coverage and acceptable performance.
Below is a list of fungicide and fungicide combinations available for use on wheat for powdery mildew, Septoria (Stagonospora) leaf blotch, and leaf rust:
1) Tilt 3.6 EC, 4.0 fl. oz/A, apply at or before flag leaf emergence
2) Bayleton 50 DF, 2-4 oz/A for powdery mildew or 4-6 oz/A for powdery mildew, Septoria and leaf rust. Use the 6 oz/A rate specifically for leaf rust control. Application should not be made within 35 days of harvest.
3) Bayleton 50 DF, 2 oz/A plus Benlate 50 DF, 4-8 oz/A for powdery mildew, Septoria and leaf rust. Application should not be made within 35 days of harvest.
4) Benlate 50 DF 4-8 oz/A plus a Mancozeb product (1.6 to 2.1 lb/A) for powdery mildew, Septoria and leaf rust. Acceptable level of control usually requires two applications, repeat application 14 days later.
5) Mancozeb products (Manzate 200, Penncozeb, Dithane DF, Dithane M-45, Dithane F-45, Dithane WSP), 1.6 to 2.1 lb/A for leaf rust and Septoria. Will require two applications, repeat application 7 to 14 days later.
We have been receiving calls about tolerance of soybeans to products containing sulfentrazone (Authority First, Authority Broadleaf/Canopy XL). These questions have arisen in response to literature Pioneer has provided to their dealers and customers. This literature indicates those varieties that are sensitive to sulfentrazone or metribuzin. Pioneer has implemented a screening procedure to test their soybean varieties for tolerance to sulfentrazone, because injury was observed in some fields in the past. We have not observed significant soybean injury from sulfentrazone in OSU herbicide trials over the past 5 years. Among surrounding universities, only Michigan State has observed significant injury, and this occurred at a rate higher than currently labeled (Michigan State has more frequent instances of herbicide injury in general, since some of their test areas have coarse soils). We are not overly concerned about the risk of soybean injury from sulfentrazone, but information such as that provided by Pioneer is welcome and should certainly be used when selecting varieties and herbicide programs. We do not have information on the response of public varieties to sulfentrazone, or varieties from seed companies other than Pioneer. If you have concerns, check with your local seed supplier to see if this information is available. With regard to metribuzin, Bayer publishes literature categorizing soybean varieties by degree of tolerance. Check with your Bayer rep to get a current copy of this literature.
In a typical year (whetever that is) we usually make a statement about switching from preplant/preemergence herbicides to postemergence herbicides when planting soybeans in late May or early June, compared to planting in late-April. This reduced need for a long-residual soil-applied program when planting late is based on two factors: 1) many weeds have already emerged by that time and are controlled by tillage or burndown herbicides, so there will be fewer weeds to deal with after planting, and 2) the soybeans should emerge and grow more rapidly in later-planted fields, so they can compete more effectively with the weeds. Over 5 years of field research, we have observed increased effectiveness of labeled and reduced rate (low rates applied sooner after planting) postemergence programs in later-planted fields.
How does this information relate to our current situation? A number of producers are currently considering a switch from soil-applied to postemergence herbicides because weeds have emerged earlier than in most years. Does early emergence mean that the entire period of weed emergence has shifted earlier in the season, and weed emergence will start to decrease in mid to late May rather than in late May to early June? Good question! Unfortunately, our database on weed emergence is so limited than we cannot with certainty come to this conclusion. We consider it too early to switch herbicide programs, even if weeds are emerging early. Our recommendation if you are considering this switch - don't switch all of your soybean acreage to total postemergence programs this early in the season. At the very least, keep some fields in a combined preplant/postemergence program, with a mininal amount of herbicide applied preplant. This reduces the overall risk, if the weather and weed emergence pattern becomes somewhat unfavorable for total postemergence herbicide effectiveness. Also, remember that a few weeds have a very long period of emergence - giant ragweed, foxtail, black nightshade, and burcucumber fall into this category. In a total postemergence program for early-planted soybeans, you run the risk of having to apply herbicides too early to catch the later weed flushes.
Rain, rain where’s my nitrogen? Precipitation the past few weeks may have affected soil nitrogen. It depends on the type of nitrogen fertilizer and soil conditions. Anytime nitrogen exists as nitrate-N in the soil, it is vulnerable to losses from leaching and denitrification. The ammonium form of nitrogen adheres to soil particles and is not vulnerable to losses until converted to nitrate-N. Conversion from ammonium to nitrate does not rapidly occur until soil temperatures stay above 50(F. Soils are cool enough in the northern part of the state that minimal N loss has occurred in fields fertilized with urea or anhydrous ammonia. Fields receiving 28% UAN may have lost 25% of the applied N, a result of losing nitrate from ammonium nitrate portion. Soil conditions are warmer in the southern part of the state. Even if some of this ammonium-N has converted to nitrate-N, losses are still probably minimal. Attempts to make up for this small loss on jointed wheat may cause more damage from the spreader equipment than the loss of N. However, in split programs where wet conditions have prevented the second application of N, additional N should be applied regardless of the growth stage. If split applications continue to be delayed, those who apply all their spring N at green-up may have better results this year.
Several factors need to be considered when determining seeding depth for corn. These include soil moisture and temperature, planting date, soil type, and tillage. A planting depth of 2 inches is often suggested for typical conditions with moist soil and an average planting date. When conditions vary from the norm, planting depth should be adjusted accordingly to optimize emergence. Don't automatically use the same depth setting you finished with last year. Also check seeding depth periodically during the course of the planting operation since soil conditions (particularly soil moisture will differ from field to field, as well as change over time).
Temperatures will generally be higher at 1 to 2 inch soil depths than at 3 inches or deeper in mid April through early May. Therefore avoid planting much deeper 1-1/2 to 2 inches during this period. This is especially important for no-till plantings where heavy residue cover exists. Under these soil conditions soil temperatures are likely to be colder and wetter than under tilled conditions. Nevertheless don't plant too shallow! Shallow plantings can result in poor nodal root formation that often lead to "rootless corn" and "floppy corn" problems - especially when soils turn hot and dry later in the spring. A depth of at least 1-1/2 inches is still desirable to maintain seed-soil contact. Unless the soil is prone to crusting problems don't be overly concerned about the ability of the seed to emerge from deeper seeding depths. A corn seedling possesses a morphological structure (the mesocotyl) which allows it to adjust to varying planting depth.
Black cutworm (BCW) and Common armyworm (CAW) pheromone traps were placed in various locations in Southwest, Central and Northwest Ohio. Results from one location in each area last week are listed below.
Miami county site #1 - Pheromone trap - BCW 15 moths / trap / week
Miami county site #1 - Pheromone trap - CAW 0 moths / trap / week
Miami county site #2 - Pheromone trap - BCW 10 moths / trap / week
Miami county site #2 - Pheromone trap - CAW 4 moth / trap / week
Hancock county site #1 - Pheromone trap - BCW 6 moths / trap / week
Hancock county site #1 - Pheromone trap - CAW 6 moths / trap / week
Hancock county site #2 - Pheromone trap - BCW 4 moths / trap / week
Hancock county site #2 - Pheromone trap - CAW 4 moth / trap / week
Western Branch site #1 - Pheromone trap - BCW 9 moths / trap / week
Western Branch site #1 - Pheromone trap - CAW 14 moths / trap / week
Western Branch site #2 - Pheromone trap - BCW 7 moths / trap / week
Western Branch site #2 - Pheromone trap - CAW 6 moth / trap / week
Not a lot of flight activity yet at either location, but the moths are present. Keep an eye on no-till fields with a healthy population of winter annuals, particularly chickweed. Additionally, recent comments in the Kentucky Pest Newsletter indicate sustained flight activity of these moths in Kentucky.
June 24: Southern Ohio Crop Diagnostic Field Day for producers, 9 am-3 pm. Cost will be $10.00 with meal included.
June 25: Agribusiness Diagnostic Field Day for consultants, agribusiness personnel, etc. 9 am-3:30 pm. Cost is $25.00 with meal included.
July 21: No-Till and Sprayer Technology Field Day. 9 am-3:30 pm. Doug Harford, Illinois precision farming and no-till farmer, will be featured speaker. Randall Reader and Erdal Ozkan are also involved.
August 6: Late Season Crop Diagnostic Field Day. 5:30 pm-9:30 pm. Pat Lipps will be featured speaker. No cost.
August 19: Southwest Ohio Corn Growers Field Day. 9:30 am-4 pm. No Cost. Emphasis will be on farmer health.
Readers can subscribe electronically to this newsletter bysending an e-mail message to:
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.
Contributors to C.O.R.N. this week include: Pat Lipps (Extension Specialist, Plant Pathology), Ann Dorrance (Extension Specialist, Plant Pathology), Mark Loux (Extension Specialist, Weed Science), Hal Willson (Extension Specialist, Entomolgy), Peter Thomison (Extension Corn Specialist), Ed Lentz (Northwest District Agronomist), Curtis Young, Jim Jasinski and Bruce Eisley (Extension Associates, Integrated Pest Management), Larry Lotz (Fayette Co.), Ray Wells (Ross Co.), Roger Bender (Shelby Co.), Howard Siegrist (Licking Co.), John Barker (Knox Co.), Greg LaBarge (Fulton Co.), Dennis Baker (Darke Co.), Max Mohler (Lima Campus), Tom Krill (Van Wert Co.), Mike Estadt (Pickaway Co.) and Steve Prochaska (Crawford Co.).Information presented above and where tradenames are used, they are supplied with the understanding that nodiscrimination 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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