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In This Issue:
A) Take the Test-Beat the Pest - Free SCN Test
B) European Corn Borer Injury, Just the Facts
C) Planting Wheat in Dry Soils
D) Dry Weather Herbicide Carryover - Considerations for Corn and Soybeans
E) Early Returns - Corn Rootworm Survey
The Ohio Soybean Council (OSC) has announced it will pay for every soybean cyst nematode (SCN) soil sample that is sent in by Ohio soybean producers to the C. Wayne Ellett Plant and Pest Diagnostic Clinic at The Ohio State University. The SCN test will be paid for by Ohio soybean checkoff dollars.
Soybean cyst nematode can rob producers of part of their soybean yield with no visible, above-ground symptoms. The only way to know for sure if you have soybean cyst nematode infested fields is with a soil test. SCN tests are being provided free of cost by Ohio soybean producer checkoff dollars through a cooperative effort of the North Central Soybean Research Program and the state soybean checkoff boards. This is the second year OSC has sponsored the program with more than 4000 soil samples submitted last year. Of the samples tested, nearly 73 percent had undetectable levels of SCN or levels below the threshold that might cause economic damage to susceptible soybeans. Approximately 26.6 percent of the samples tested showed SCN present at a level that would damage susceptible soybeans. Plus 6.4 percent of those samples had SCN levels higher than those suggested for resistant beans.
It is important to follow a few simple guidelines when sampling field for SCN testing. Soil samples should be taken with a soil probe or trowel and placed in a plastic bag. The SCN sample should be kept cool. During the growing season, collect samples from suspect areas and inspect the roots for SCN females. Following harvest or before planting, collect multiple soil cores (10-20 cores per 10-20 acres) at random by walking in a Z- or W- pattern. Mix the soil in a pail and place a healthy pint of the mixed soil in the bag. It is recommended to test fields for SCN the fall before a soybean crop.
Growers may submit the samples for free testing to : S. Wayne Ellett Plant and Pest Diagnostic Clinic, The Ohio State University, 2021 Coffey Rd, Columbus, Ohio 43210. Sample bags and reporting forms can be obtained from your local Ohio State University extension agent or by contacting the C. Wayne Ellett Plant and Pest Clinic at (614) 292-5006. Additional information about SCN is available in OSU Extension Fact Sheet AS-39-98.
Or, you may drop samples off at the Ohio Soybean Council booth at Farm Science Review at 575 Soybean Avenue.
European corn borer injury in three non-Bt isolines of Bt-corn hybrids in a trial at the Northwestern O.A.R.D.C. Branch Station averaged 1.08 cavities per plant compared to an average injury level of 0.55 cavities per plant found the previous week in a trial at the Western O.A.R.D.C. Branch Station. The injury level of 1.08 cavities per plant may or may not have a significant effect on yield. In 1997 trials conducted at the Northwestern Branch Station, corn borer injury in non-Bt isolines averaged 1.66 cavities per plant and had no significant difference in yields between the Bt-corn-hybrids and the equivalent non-Bt isolines.
This is the third year that we have conducted comparison trials between a set of Bt-corn hybrids and their equivalent isolines at both the Western and Northwestern Branch Stations. Over this three-year period, corn borer injury in non-Bt hybrids has averaged 0.54 cavities per plant at the Western Branch Station and 0.74 cavities per plant at the Northwestern Branch Station. The corn borer injury results accumulated to date from these two locations raises questions regarding the economic benefits of investing in Bt-corn hybrids if such technology must be purchased at premium prices.
By the end of this week, northern Ohio will have reached the fly free date, the optimum calendar date for planting wheat. However, some of the soils in these areas may still be quite dry. In dry years, extra care must be given to insure germination and adequate fall growth for wheat. Some of these management practices include:
1) Conserve soil moisture, plant no-till.
2) Use high quality seed treated with the proper fungicides.
3) Calibrate and use the correct drill settings. Soils may be hard at planting, adjustments may be needed to insure proper seeding depth. Seeding depth should be around 1 - 1 1/2 inches.
4) Apply necessary fertilizer. Phosphorus is needed when soil test levels are below 40 ppm; potash is needed when test levels are below 130, 160 and 185 ppm for soils having a CEC of 10, 20, or 30, respectively. Twenty to thirty pounds of nitrogen should also be applied in the fall.
5) Use proper seeding rates. Seeding rates should be 1.6-2.0 million seeds per acre. The germination rate and seeds per pound (found on the tag or bag) must be known to determine seeding rate. The target seed rate divided by the number of seeds per pound will give the pounds of seed needed per acre. For example, if there were 16,000 seeds per pound, 100 pounds would be required to plant 1.6 million seeds per acre.
More information on wheat can be found in the publication "Guidelines to Improved Wheat Yields in Ohio", Plant Pathology Series 107
Dry weather is a major factor in the carryover potential of most persistent herbicides except chlorimuron, which has occurred almost exclusively in high pH areas. Based on previous experience, the herbicides posing the greatest risk of carryover from soybeans to corn are:
Imazaquin (Steel, Scepter, Squadron, Tri-Scept, Detail) - Rainfall following application is the most critical factor that determines the risk of imazaquin carryover. The label of all imazquin-containing products contains a statement indicating that corn can be planted 9 1/2 months after application only if 15 inches of rain is received between 2 weeks before application and November 15. If less than 15 inches is received, only imidazolinone-resistant (IR, IMR) or -tolerant seed (IT) should be planted. Both types of corn will provide protection against imazaquin carryover. The risk of imazaquin carryover also increases at low soil pH (less than 5.5) and as soil organic matter and clay content increase. Imazethapyr (Pursuit) has generally not caused carryover problems to corn in Ohio. However, we suspect that the combination of imazethapyr and imazaquin in Steel could result in carryover problems where rainfall is low, even though imazaquin is present at a reduced rate in this product.
Chlorimuron (Canopy, Canopy XL, Classic, Synchrony) - Dry weather does not seem to significantly increase the risk of chlorimuron carryover. We speculate that there may be some marginal pH situations (6.8 to low 7's) where corn escapes chlorimuron carryover in years of adequate moisture, and these may be more problematic following a dry year. In a suspected chlorimuron carryover situation, planting of imidazolinone resistant corn (IR or IMR) will protect against injury. Imidazolinone-tolerant (IT) corn does not provide enough protection against chlorimuron carryover.
Fomesafen (Reflex, Flexstar) - Carryover has been very rare in Ohio, but would be most likely in fields where Reflex or Flexstar was applied late in the season with continued dry weather after application. Risk of carryover may be high where Flexstar was used late in the season to control ragweed that escaped earlier applications of ALS inhibitors.
Clomazone (Command) - Corn is much more tolerant than small grains or forages to carryover of Command. Research has shown Command degradation to be much reduced under dry conditions. The Command label also indicates that risk of carryover is greater when pH is below 5.9. This is due to reduced activity of the microorganisms responsible for clomazone degradation is soil.
With regard to risk of carryover of corn herbicides to soybeans under dry conditions, herbicides of greatest concern are the triazines (atrazine, simazine) and prosulfuron (Exceed, Spirit). Carryover of triazines to soybeans has been rare at the current labeled rates of atrazine and simazine. Dry weather will increase the risk of carryover, although is is difficult to say how much based on the lack of carryover in recent years. Carryover is most likely where rates are highest, as in the combinations of one pound of simazine with atrazine premixes. Carryover of prosulfuron is most likely under dry conditions, where soil pH is high (greater than 7.8), and if applied late in the season. The Exceed label (for south of I-70) states that only corn or small grains should be planted the year after application if soil pH is greater than 7.8, less than one inch of rain occurs within one month of application, or less than 12 inches of rain occurs within 5 months of application. The Spirit label (for north of I-70) is similar, but does allow planting of STS soybeans if rainfall is inadequate as long as soil pH is less than 7.8.
Our information is fairly limited with regard to the risk of injury to various crops from carryover of several new herbicides under dry conditions. These include FirstRate, Authority, and Balance. We have no evidence to suggest that these are problematic in this regard, but we suggest you contact the local sales representative if you have concerns. In general, the effects of herbicide carryover are most likely to be observed in areas of sprayer overlap. Conditions that limit crop growth, such as cold weather or compaction, often result in increased injury from carryover. These conditions may also prevent crops from recovering from early-season injury. The full expression of carryover effects are thus dependent upon next year's growing conditions as well as the amount of herbicide persisting from year to year.
Trap data generated from the deployment of Pherocon AM traps in soybean fields to monitor western corn rootworm has been reported by about 20 county Extension programs. In general, average trap collections of western corn rootworm beetles are running about 50% higher than that of 1998. The distribution of first year corn rootworm activity in Ohio continues to be most evident in the western counties (west of Interstate 75). The most eastern counties exhibiting some indication of first year corn rootworm activity are Allen, Shelby and Champaign counties. However, trap collections reported rarely approach the economic threshold of two beetles per trap per day, which would indicate a potential need for a rootworm insecticide in first year corn following soybeans. The highest average trap catches of rootworm in soybeans have been in Van Wert County. Soil insecticide trials conducted this year at the Farm Focus site found minimal rootworm injury in the untreated check plots, but rootworm injury in soil insecticide trials on nearby second year corn was quite severe.
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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: State Specialists: Anne Dorrance (Plant Pathology), Pat Lipps (Plant Pathology), Hal Willson (Entomology), and Mark Loux (Horticulture & Crop Science); District Specialist: Ed Lentz (Agronomy); Extension Agents: Dave Jones (Allen), Barry Ward (Champaign), Steve Prochaska (Crawford), Greg LaBarge (Fulton), Glen Arnold (Putnam), Clark Hutson (Seneca), Roger Bender (Shelby), and Andy Kleinschmidt (Van Wert).
Editor: Ed Lentz Web Editor: Nathan Watermeier
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.
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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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