CFAES Give Today
Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2008-05

Dates Covered: 
March 4, 2008 - March 19, 2008
Harold Watters

Our Annual Prediction of Flea Beetle Activity and Stewart’s Disease for the 2008 Corn Crop

Authors: Ron Hammond, Pierce Paul, Andy Michel, Dennis Mills, Bruce Eisley

The bacterium causing Stewart's bacterial leaf blight is carried and spread by the adult corn flea beetles. The beetle over-winters as an adult in the soil near corn fields. Flea beetle adults become active in the spring when the soil temperatures reach 65 F. Adults are most active on sunny, warm, windless days. If the adult fed on diseased corn in the late summer or fall, it may carry the bacterium that causes Stewart's disease of corn in its gut over the winter. In the spring as the corn emerges, the flea beetles feed on the young plants and spread the bacterium which in turn causes seedling wilt and leaf blight. The occurrence of Stewart's bacterial disease is totally dependent on the level of bacteria-carrying flea beetle survival over the winter. For many years the winter temperatures have been used to predict the risk of Stewart's disease because higher populations of the flea beetle survive during mild winters than during cold winters. The 'flea beetle index' is calculated as the sum of the average temperatures (Fahrenheit) of December, January and February.
- Index values less than 90 indicate negligible disease threat,
- 90-95 indicate low to moderate levels,
- 95-100 indicate moderate to severe and
- values over 100 predict severe disease threat.

We checked the average temperature for those months at several locations in Ohio to determine the risk level according to the 'flea beetle index' for 2008. The locations and the corresponding indexes were:
Hoytville, 84.4;
Wooster, 88.4;
Ashtabula, 87.4;
South Charleston, 90.4;
Jackson, 99.7; and
Piketon, 100.3.
These numbers would indicate that the risk of Stewart's bacterial leaf blight is low to moderate in northern and west central Ohio with a higher disease risk in southern Ohio.

These values are very similar to those from last winter, 2007. However, when comparing the temperatures last year to the past 3 months, we see a very different picture. Last year, December and January were relatively warm, while February was an extremely cold month. This year, these 3 months have, on average, been more typical of the temperatures one would expect, without any month being neither extremely warm nor cold.

As usually, we would still recommend that growers scout for flea beetles, especially if they have planted a hybrid that is susceptible to Stewart's disease. For growers wishing to take preventive action against flea beetle, a commercially applied insecticide seed treatment such as Cruiser and Poncho are labeled for flea beetles. You can see pictures of flea beetle injury and Stewart’s bacterial blight, and get additional information on Stewart's disease of corn, on the Ohio Field Crop Disease web site at Additional information on the flea beetle can be obtained from OSU Extension Fact Sheet CV-1000-94.

Preventive Insect Control on Field Crops

Authors: Ron Hammond, Andy Michel, Bruce Eisley

Although we do not recommend taking preventive measures against insect pests on a widespread basis, there are certain situations where such actions may be acceptable. Using preventive tactics should be based on a history of problems in a field, sampling for the insects, or cropping practices being used.

Taking preventive action against corn rootworm larvae continues to be an appropriate tactic when growing corn following corn. Growers have numerous choices, including transgenic corn hybrids, soil insecticides which still offer excellent control, and finally higher rates of seed treatments, although this latter tactic is best used when rootworm pressure is only expected to be relatively low to moderate. Seed treatments do not hold up when rootworm pressure is severe.

Where the first year western corn rootworm variant occurs, mainly western and northwestern Ohio, growers must decide on the need for preventive tactics. The variant continued to be observed in soybean in much higher numbers in 2007 in these areas. If in these locations, we suggest giving consideration to taking preventive action against the rootworm in first year corn. Remember that in areas without the first year variant, rotation is still the most preferred preventive tactic to make. If choosing to use a treatment, you have the transgenic hybrids, soil insecticides, and seed treatments.

For European corn borer, we have numerous transgenic corn hybrids that give outstanding control. The decision to use them should be based on having had a history of borer problems. We would point out that the corn borer problem has not increased throughout Ohio, so widespread use of these transgenic is probably not necessary. But for those growers wanting to preventively manage this pest, transgenic hybrids are an outstanding choice. Where we do see a greater need for these hybrids specifically for borer control is for corn that is planted in late May or early June. In those situations, we often see greater problems from European corn borer, and usually recommend growers consider these transgenics.

In this issue of the CORN newsletter, we have already discussed the potential for flea beetle problems and the likelihood of Stewart’s bacterial wilt. Growers planting corn hybrids that are more susceptible to Stewart’s wilt might consider one of the commercially-applied seed treatments. They are labeled for corn flea beetle control and might help keep populations and subsequent Stewart’s wilt down.

The use of commercially-applied seed treatments is a preventive treatment that is also recommended against many insects including seedcorn maggot, wireworms, white grubs, and black cutworm. Although we do not recommend seed treatments for “plant health” purposes, we do see a need for them where any of these insect pests have historically caused concern. The problem is that for most of these pests, we do not have good predictive abilities as to where and when they will be a problem. Growers should examine the history of their field as to whether they have experienced previous problems. If the answer is yes, seed treatments should help to alleviate injury. If the answer is no, and growers have not had problems in the past, we do not think “potential” problems justifies the additional cost. One pest where we do have predictive abilities is seedcorn maggot. When growers incorporate green organic matter in the soil in the spring, including old alfalfa fields, cover crops, or even heavy weed growth, the chances of enhanced numbers of seedcorn maggots and subsequent plant stand reductions is high. Thus, we do recommend seed treatments for both corn and soybeans when planting in fields where green, organic matter is being plowed or tilled into the soil.

Black cutworm is an insect that we are hearing about from growers every year. Because the adult migrates from the south each year, we are not able to offer any predictions about problems. We still think the best management for black cutworm is by scouting fields beginning at early emergence; we do have a number of insecticides that can be applied as rescue treatments for cutworm. However, if a field has a history of cutworm damage and/or the field has a high population of winter annuals such as chickweed, then a preventive tactic can be used. A grower could apply a soil insecticide at planting or include an insecticide with the pre-emergent herbicide. Alternatively, a grower could use Herculex 1 or Herculex XTRA transgenic corn hybrids because these have cutworm activity. However, we do not recommend seed treatments because our data and experience from past years suggest that seed treatments are unable to provide acceptable cutworm control.

We then need to examine preventive treatments on soybeans. Although we are predicting low soybean aphid populations this summer, we would remind growers that we continue to NOT recommend seed treatments for soybean aphid control. Our data from previous years indicate that seed treatments do not offer control of aphids when needed, which is in late July and August. Hopefully no control tactics against the aphid will be necessary this year.

The situation with bean leaf beetle on soybean is slightly different. Although these treatments will control the beetles in early summer, this population of beetles does not cause that much leaf injury unless they are in extremely high numbers, and we seldom see this. Additionally, seed treatments will not limit later population growth in mid to late summer. Thus, we do not recommend seed treatments as a preventive measure to prevent feeding by this insect.

When producing soybean for seed or food grade soybeans and in other situations where seed quality is a major issue, we slightly change our recommendations for bean leaf beetle control. This change is because of our concern with the beetle’s ability to vector bean pod mottle virus. For growers who choose to control overwintering bean leaf beetles to limit virus transmission, we would recommend an early season foliar spray after plant emergence, followed by a second spray in July for the first generation beetles. Because seed treatments will offer control of the overwinter beetles and reduce feeding injury, growers might want to use seed treatments to replace the early season foliar spray. Currently, we do not have all the answers as to whether controlling the overwintered beetles with seed treatments will reduce virus transmission. Data from other universities suggest that this approach might not give economic control of the virus. However, growers might wish to try these seed treatments on a few fields to see if they work.

Nitrogen Credits for Corn after Soybeans

Authors: Edwin Lentz, Robert Mullen

Some producers across the state experienced failed soybean crops last year due to the lack of moisture or from flooding, and now they are wondering – do I take a nitrogen credit for that soybean crop even though it never reached maturity? The simple answer is yes you should take a credit (around 30 pounds) for that soybean crop even though it did not reach full maturity.

Traditionally, the hypothesized reason for the nitrogen credit for a corn crop following soybean is because the soybean crop biologically fixes nitrogen that it leaves in the soil that can be utilized by the subsequent corn crop. One reason for questioning this hypothesis is that soybean plants will take up soil nitrogen if it is present (foregoing nodule formation and nitrogen fixation). A study conducted in the early 90s in Iowa reveals that this hypothesis is not likely to be true. The study shows that the primary difference between corn after corn and corn after soybeans is the amount and speed of immobilization (nitrogen removal from soil solution) that occurs (Green and Blackmer, 1995). Corn returns a high amount of biomass that has a large carbon to nitrogen ratio, and degradation of that residue requires a net nitrogen immobilization that takes a relatively long period of time. Soybean returns a much lower amount of residue that degrades much quicker. It does result in immobilization, but the extent of immobilization is much lower and the process proceeds much quicker.

Take home message – the biologically fixed nitrogen contained in soybean root nodules is unlikely to be a major contributor to the nitrogen credit that we recommend for a subsequent corn crop. The larger issue is the amount and nature of plant material returned to the soil that soil microbes have to degrade. So even though last year’s soybean crop may have failed, you should still plan on taking a nitrogen credit if that field is going to corn this spring. If you are utilizing Ohio State University’s new economic-based nitrogen rate calculator, the 30 pound credit will be included in the recommendation, and you will not have to take an additional credit. The Economic Nitrogen Management Spreadsheet is available at:

Urease Inhibitors

Authors: Robert Mullen, Edwin Lentz

As nitrogen prices remain high the question of nitrogen stabilizers always comes up. So under what conditions are you most likely to see an economical benefit to their use? It is important to understand what these inhibitors do, so that we know where they will have the greatest potential value.

Any urease inhibitor is only of value for urea-based fertilizers. Once urea goes into soil solution it requires exposure to the enzyme urease to degrade the organic compound to form ammonium. The first product on the way to the stable ammonium ion is ammonia and that is a gas subject to potential volatilization loss (floats away from the soil surface). Urease inhibitors deactivate the enzyme keeping the organic compound around longer until rain (or irrigation) incorporates the material into the soil. Any urea based fertilizer that is incorporated or injected below the soil surface should not require an urease inhibitor. Surface applications can benefit from urease inhibitors, but the need for the inhibitor is directly related to rainfall. Surface application of urea-based fertilizer followed quickly by rainfall is not likely to lose much nitrogen by volatilization, but you have to trust the weather forecast. Essentially, the urease inhibitor acts as an insurance policy in case rainfall does not come quickly enough.

Tillage is also a major player in determining the need for an urease inhibitor. Tillage systems that maintain a large amount of residue on the soil surface have an abundance of urease and do not allow incorporation of the urea-based fertilizer. Therefore, surface applications of urea-based fertilizers are more likely to benefit from urease inhibitors.

The need for urease inhibitors is also dependent upon the rate of nitrogen being applied. The potential for urease inhibitors is typically greatest when the amount of nitrogen being applied is lean. High rates of nitrogen are less likely to show a positive economic response to urease inhibitors because some loss can be tolerated with no agronomic penalty. Lean rates of nitrogen can benefit because the rate of nitrogen applied may be limiting and we desire to keep all that was supplied in the soil system.

Data collected last year at the Northwest and Western Research Stations reveals that the greatest potential benefit for urease inhibitors is in no-till systems when urea is broadcast, surface applied. Dribble applications of UAN (urea-ammonium nitrate - 28-0-0) in a band did not benefit from inclusion of a urease inhibitor at either location.

The previous discussion concerned urease inhibitor applications for corn. Questions also come up concerning wheat. The process is the same for wheat as corn. Granted, wheat growing in the spring would be similar to fields covered with residue, limiting the opportunity for the urea-based fertilizer to quickly incorporate in the soil. However, cool conditions generally associated with spring topdress also limits the activity of the urease enzyme. Thus the cooler temperatures associated with spring topdress time is adequate to minimize volatilization until a rain event occurs. If we had a stretch of 80 degree days, and dry conditions for several weeks, volatilization may become a problem – but even the urease inhibitor only has an effective time frame of about 10 -14 days and mostly 7 days.

Consider rainfall, tillage, and nitrogen rate when deciding upon the inclusion of a urease inhibitor for corn production and in wheat, since soil conditions are generally cool and the chance is great for rain in March and April, we would anticipate little benefit from a urease inhibitor.

Weed Management Webpage Updates

Authors: Harold Watters

We have noticed this winter at Pesticide Applicator Recertification meetings that more of you are taking notes when we discuss possible weed resistance issues and the need for the use of pre-emergent herbicides in both corn and soybeans to forestall possible resistance development.

There are a number of new additions to the Weed Science area of the Agronomic Crops Team webpages: including most of the Weed Science presentations from this winter as well as the two-page recommendation sheets. Also posted are the weed resistance maps indicating resistance by county.

The updated 2008 Weed Control Guide makes good reading for weed management issues not just for product recommendations and is available from most county Extension offices in Ohio and Indiana as well as from the above noted Weeds website.

Plan Now for Double Cropping Wheat & Soybeans

Authors: Jim Beuerlein

Double cropping drastically reduces the elapsed time between successive crops and therefore can greatly increase the disease pressure for both crops. Where double cropping is practiced, the beneficial effects of crop rotation (weed, insect, and disease control) are totally negated.

There are two primary requirements for profitable multiple cropping:
- There must be adequate time for the production of a second crop.
- There must be adequate water to produce two crops, whether from stored soil moisture, rainfall, or irrigation.

Because the soybean crop is photoperiod sensitive and matures in response to day length, it is ideally suited for multiple cropping systems where planting dates for the second crop are later in the season and can be variable due to weather.

Currently, most double cropping systems depend solely on a combination of rainfall and stored soil moisture to supply adequate water for two crops. Irrigation can be used as a supplement for soils with a less than adequate water supplying capacity and/or inadequate rainfall. While irrigation can greatly increase the consistency of crop yields, it also increases the cost of production. If the top 3 inches of soil is dry when the second crop is planted, germination is greatly slowed until the receipt of adequate rainfall. There also must be adequate soil moisture to enable the root system to grow into moist soil where water availability is more consistent. Because the water requirement is so large for double cropping, it is generally most successful on soils with large water supplying capacities that are sometimes referred to as “good corn soils.”

Early planting of the second crop is essential for success, which requires harvest of the wheat as early as possible. Potential double crop soybean yield decreases by one bushel for each day that planting is delayed after June 20. Early wheat harvest can be accomplished by planting an early to mid-maturity wheat variety soon after the fly-free date in the fall and harvesting when the grain moisture decreases to 18% to 20% and then using air with or without supplemental heat to dry the grain. These actions combined can save several days that would normally be used to field-dry wheat to 10 to 14 percent moisture. If a grower wishes to maximize wheat production because of the high value of wheat relative to a following crop, early harvest may be less important.

Below-normal temperatures in June delay wheat maturation, which may require growers to reconsider planting the second crop. For someone considering double cropping, it may be necessary to have two wheat varieties differing in maturity available in the event that wheat maturation is delayed. In southern Ohio, soybean varieties with maturity ratings of 3.4 to 3.9 will usually mature before the first freezing temperature if planted in June. Other than selecting a variety that matures before the first freeze, variety selection is not as important for double cropping as it is for a full season crop. Ohio studies have shown that early planting and July-August rainfall have a much greater impact on double crop soybean yield than does variety.

Straw remaining after grain harvest must be managed so as not to interfere with planting the second crop. Some stubble may be left to provide mulch cover. Leaving an 8 to 12-inch stubble with the combine and baling the cut straw is an efficient practice and marketing the straw adds income from winter wheat. Alternatively, the straw can be chopped and spread evenly on the field. Usually, a no-till planter or no-till drill can plant through chopped straw, if the soil is not excessively wet or dry and hard.

Soil moisture at the time of planting the second crop is critical for its success, because average rainfall in July and August often does not replace the moisture used by the second crop. In most years, moisture used by wheat in May and June is replaced by rainfall, but in dry seasons some subsoil moisture may be used, leaving an inadequate amount of water for the second crop. Soils with low available water holding capacity are not suitable for double cropping soybeans. Generally, such soils are poorly drained, somewhat poorly drained without tile, eroded, or sandy. Growers should also be aware of the water holding capacity of their soil, and rainfall in May and June when planning to double crop soybeans after wheat. An important rule of thumb to consider is: “if June is dry, don’t try to double crop.” Increased nitrogen application for the small grain produces more vegetation, which increases soil moisture use. Because wheat uses moisture from the upper 8 to 12 inches of soil, growers should be aware of the moisture remaining below that depth.

Because of the short growing season remaining after wheat harvest and other time constraints, double crop soybeans should be planted no-till. The surface residue associated with no-tillage planting helps reduce moisture lost by evaporation and increases rainfall infiltration. In dry years, no-tillage planting can make a difference between satisfactory and unsatisfactory seed germination resulting from the moisture saved. A goal should be to plant the second crop on the same day the first is harvested. Narrow row, no-tillage planters equipped with residue cutting coulters and double disk openers have performed well for double cropping, but modern no-till drills are excellent implements also. Because double crop soybeans do not grow very tall, they should be planted in narrow rows (7.5”) and planted at high seeding rates (minimum of 250,000 seeds per acre) to obtain maximum leaf canopy and yield.

Weed control is not especially difficult with ordinary double cropping. The break between crops allows the use of a nonselective herbicide, such as Gramoxone Extra or glyphosate, to remove established weeds and the use of glyphosate and glyphosate tolerant soybeans can be used to control weeds that develop following soybean planting. Occasionally, broadleaf weeds, such as Canada thistle or ragweed, become established in winter wheat fields and interfere with grain harvest or with the following soybean crop. These weeds can be controlled in the wheat crop with application of 2,4-D amine; 2,4-D ester; MCPA; dicamba; or Buctril. At the wheat hard-dough stage, 2,4-D amine can be used to control some weeds that might be a problem for the following soybeans. Always read the herbicide label to ensure compliance with requirements for use.

Registration for Drainage School due by Friday, March 7

Authors: Larry Brown

There are still a few open seats left at the 2008 Overholt Drainage School. The school will be held March 17-21, 2008 at the Hancock Agricultural Service Center, in Findlay, Ohio. For the agenda see:

There are three sessions.
- Session I is 1 and 1/2 days on March 17-18, and focuses on Laser Surveying, Topographic Mapping, & GPS Mapping (Monday 9:00 AM to Tuesday 11:50 AM).
- Session 2 is 2 days, March 18-20, and is on Agricultural Subsurface Drainage Design, & Installation (Tuesday 1:15 PM to Thursday 11:50 AM).
- Session 3 is March 20-21 (1 1/2 days) and will focus on Drainage Water Management: Controlled Drainage System Design and Installation (Thursday 1:15 to 9:00 PM); and Agricultural Constructed Wetlands (Friday 8:00 AM to 3:00 PM).
Sessions 1 and 2 should be attended in their entirety.

Registrations must be received by 5:00 PM on Friday, March 7. Please contact Larry Brown at 614.292.3826 or for more information.

Introduction to Organic Crop Production Program

Authors: Deb Stinner

The demand for organic food keeps growing, and an upcoming workshop will share with Ohio farmers how they can start to profit from it.

Organics 101: An Introduction to Organic Crop Production, sponsored by the Ohio Ecological Food and Farm Association (OEFFA) and the Ohio State University Organic Food & Farming Education and Research (OFFER) Program, will run from 8:30 am - 4:00 pm on Thursday, March 20, 2008 at the university's Ohio Agricultural Research and Development Center (OARDC), 1680 Madison Avenue in Wooster, Ohio.

The program will feature organic farmers and OFFER researchers, who together will present the latest and best recommendations for transitioning to organic production.

Marketing organic crops, the economics of organic production, the organic certification process, organic certification standards and finding approved production inputs will be among the topics. So will crop rotations, pest management and soil biology.

The growing demand for organic food presents a great opportunity for Ohio farmers. Any Ohio farmer who is looking for information on organic crop production is encouraged to attend this workshop.

Preregistration for this workshop is $25.00 if received by March 10. Registration received after March 10 is $30.00. To register, send your name, address, telephone number (optional), email address (optional) and payment to Kathy Bielek, 201 Thorne Hall, OARDC, Wooster OH 44691. Make checks payable to OSU/OFFER.

More information is available on the OEFFA website (, or contact Kathy Bielek, OARDC, at (330) 202-3528, or , or Mike Anderson, OEFFA, at (614) 421-2022, or .

March Agronomic Offerings from the AgCrops Calendar

Authors: Harold Watters

The entire calendar is available on the Agronomic Crops Team website:

March 12
Seneca County OSU Extension and SWCD Agronomy Night
Start Time: 5:00 p.m.

County of Meeting Location: Seneca

Name of Meeting Place: Safety Building, Seneca County Fairgrounds
Meeting Place Address: 126 Hopewell Avenue 

Meeting Place Town: Tiffin, Ohio

CCA Credits Offered: YES
PAT Credits Offered: Private: NO Commercial: NO
Meeting Coordinator Name: Ed Lentz and Mark Fritz

Phone Number: 419/447-7073, 419/447-9722

March 26
The Tri-County Agronomy Day for corn, and soybean producers in Champaign, Logan and Union Counties will be held March 26, 2008, from 10:00 a.m. to 3:00 p.m. at the Vineyard Christian Fellowship Church, located at 624 Twp Rd 55, Bellefontaine, OH 43311.

For the program price of $5, producers will receive last minute updates from state Extension specialists and local Extension professionals. Please pre-register by telephone to the Logan County Extension office (937 599-4227) to allow us to plan meal arrangements and handouts, or by email to Wes Haun,

Archive Issue Contributors: 

Anne Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel and Bruce Eisley (Entomology), Robert Mullen (Soil Fertility), Ed Lentz (Agronomy), Jim Beuerlein (Soybean & Small Grain Production), Larry Brown (Ag Engineering), Deb Stinner (Agroecosystems) and Mark Loux (Weed Science). Extension Agents: Todd Mangen (Mercer), Roger Bender (Shelby), Howard Siecrist (Licking), Glen Arnold (Putnam), Greg LaBarge (Fulton), Gary Wilson (Hancock), Steve Foster (Darke), Harold Watters (Champaign), Mike Gastier (Huron), and Bruce Clevenger (Defiance).

Crop Observation and Recommendation Network

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.