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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2007-05

Dates Covered: 
March 6, 2007 - March 20, 2007
Harold Watters

Predicting Flea Beetle Activity and Stewart’s Disease for the 2007 Corn Crop

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

The bacterium causing Stewart's bacterial leaf blight is carried and spread by the adult corn flea beetles. In the spring, as corn emerges from the ground, 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.

Summary of Flea Beetle Index Classifications

Index values Disease Threat Level
less than 90 negligible
90-95 low to moderate
95-100 moderate to severe
over 100 severe.

We checked the average temperature for December, January and February at several locations in Ohio to determine the risk level according to the 'flea beetle index' for 2007.

Flea Beetle Index for Select Ohio Locations

Location Flea Beetle Index
Hoytville 84.4
Ashtabula 86.6
Wooster 88.7
Delaware 89.0
Jackson 97.7

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.

However, in determining these numbers, we would remind growers that while December and January were relatively warm, with average temperatures around 36-39 degrees F in December and 30-35 degrees F in January, February was an extremely cold month with averages around 18-23 degrees F. If February’s temperatures had been normal, our risk levels would have been much higher. Because of the major difference between the relatively warm temperatures during December and January and the very cold temperatures in February, we would urge caution in relying completely on these predictions. We would recommend that growers scout their corn fields for the presence of flea beetles, especially if they know they have planted a hybrid that is susceptible to Stewart's disease. For those growers wishing to take preventive action against flea beetle, commercially applied insecticide seed treatments Cruiser and Poncho, or the grower applied products Concur and Latitude, are labeled for flea beetles.

Flea beetle adults become active in the spring when the soil temperatures reach 65 F. Adults are most active on sunny, warm, windless days. They hide in cracks in the soil during windy, cool or cloudy days. After feeding and mating, adult females lay eggs at the base of the corn plants. Larvae feed on corn roots and are full grown in about two weeks. There are at least two generations per year in Ohio. The beetle over-winters as an adult in the soil near corn fields. It prefers bluegrass sod, but may be found in fence rows, roadsides and woods. 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. 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, Bruce Eisley

Growers are faced with numerous decisions in the spring, including whether to use preventive insecticide treatments. Although we do not recommend taking preventive measures on a widespread basis, there are certain conditions where we do suggest preventive management tactics. The decision to use preventive treatments should be based on a history of problems in a field, sampling for the insects, or cropping practices being used.

As has always been the case, we would still recommend a preventive treatment be considered for corn rootworm larvae management when growing corn following corn. Because there appears to be greater interest in growing more corn this year, the need for rootworm control is much greater. In those cases, we would recommend using either a soil insecticide, a commercially applied seed treatment of either Cruiser CRW or Poncho 1250 at their high rates if in an area of low to moderate rootworm pressure (seed treatments will NOT adequately control severe larval pressure), or a transgenic corn hybrid with resistance to rootworm larvae. We do not recommend one over the other, and feel the decision is best left to the grower based on his/her own farming practices and economics. For those corn growers in the western and northwestern Ohio where the western corn rootworm variant has become a much greater concern, we suggest giving strong consideration to taking preventive action against the rootworm in first year corn following soybeans. The variant was observed in soybean in much higher numbers in 2006 than in any previous year. See last year’s CORN article on making the decision to treat in first year corn (CORN Newsletter 2006-33, October 3-9, 2006;

For European corn borer, we can still scout and use insecticides for control or we have transgenic corn hybrids that give outstanding control of borer populations. The decision to use them should be based on a number of things, including having had a history of borer problems in the past, and a history of treating for them in previous years. This problem usually only occurs in isolated fields for most growers. 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 perhaps a greater need for these hybrids are for late planted corn, 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 another article in this CORN newsletter, we discuss 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, Cruiser and Poncho, at either rate. Both are labeled for corn flea beetle control and might help keep populations and subsequent Stewart’s wilt down.

The use of seed treatments, either commercially applied or grower applied, is a preventive treatment that is also recommended against many insects including certain soil pests such as seedcorn maggot, wireworms, and white grubs, and other pests including 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 will help to alleviate future injury. If the answer is no, and growers have not had problems in the past, we do not think problems will begin occurring in the future. However, there is one pest where we do have predictive abilities, and that is with seedcorn maggots. As we have written in the past, 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 another insect that we are concerned about each year in corn. Last year was an extremely bad year for this insect. However, we are unable to predict the potential for 2007 because it is a migrant from the south and early spring temperatures may play a role in whether it will be a problem or not. We still think the best management for cutworm can be obtained by scouting fields regularly beginning at early emergence because unlike some of the other insects we have discussed, such as seedcorn maggot, wireworms or grubs, 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 treatment could be applied at planting by using either a soil insecticide at planting, the inclusion of an insecticide with the pre-emergent herbicide or the use of Herculex 1 or Herculex XTRA corn hybrids since these have cutworm activity. We do not recommend seed treatments because data and our experience from last year suggest that seed treatments are unable to prevent black cutworm injury, and foliar treatments might still be necessary.

Finally, there is much discussion of seed treatments on soybeans for soybean aphid and bean leaf beetle control. The potential for use against the aphid is important because we anticipate heavy soybean aphid pressure this summer. As discussed in previous CORN newsletters, we do NOT recommend them for soybean aphid control. It is too difficult to predict which fields might have aphid problems, and more importantly, our data from last year indicates seed treatments do not offer control of them. We will continue to recommend scouting, using the 250 aphids/plant threshold, and spraying a foliar insecticide.

The situation with bean leaf beetle on soybean is different. For general control of overwintering bean leaf beetle, we do not recommend seed treatments. 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 more importantly, those populations are too difficult to predict. Seed treatments will not limit later population growth in mid to late summer. As with the aphids, we would rather see growers scout their fields for bean leaf beetle in mid to late summer and use a foliar insecticide as beetle densities do reach threshold levels.

The recommendations for bean leaf beetle control is somewhat different for seed growers, food grade soybeans, and other situations where seed quality is a major issue at the end of the summer. This greater concern is related to the beetle’s ability to vector bean pod mottle virus. For growers who decide to control overwintering bean leaf beetles to limit virus transmission, we would normally recommend an early season foliar spray after plant emergence when beetles are entering the field, followed by a second spray in July against the first generation. Because seed treatments will offer some control of the overwinter beetles and reduce feeding injury, we would suggest that seed treatments be used in a few fields to see if they can replace the early season foliar spray. Although we do not have all the answers as to whether this will reduce virus transmission, we do recommend that growers who follow the two-spray regime give seed treatments a try in a few fields.

Controlling Soybean Pests in 2007

Authors: Jim Beuerlein, Ron Hammond, Anne Dorrance, Dennis Mills

There are several late season soybean insect and disease problems that we will have to deal with in 2007. Most fields are planted in narrow (7.5-inch) rows and will be sprayed in late July or in August, well after the soybean canopy has closed which will cause a yield loss due to soybean plants being run down. Fortunately, many sprayers have narrow tires so only two rows may be run down as the sprayer crosses a field, but the actual loss depends in the row spacing and size of the spraying equipment. Running down two rows with each sprayer pass through a 50 bushel crop worth $7.50 per bushel will cause a $7.81per acre loss. Leaving skip rows for those tire tracks, will cost only $1.94 per acre because some rows are not planted which reduces the seed cost. It is always less expensive to use a skip-row system than to run down some of the crop with a sprayer.

When forming skip rows it is important that they be the correct distance apart to accommodate the sprayer’s tires. Many sprayers are adjustable and can accommodate a wheel spacing of about eight to twelve feet. The ideal combination of drill and sprayer width is when the sprayer is three times as wide as the drill. With that combination the sprayer will use the 2nd, 5th, 8th, etc. pass of the drill when making applications. If the sprayer is either two or four times as wide as the drill, the first sprayer pass should be positioned to spray from the edge of the field to the center of a drill pass by disabling nozzles on the end of the sprayer. For the remainder of the field use all the spray boom and the appropriate skip rows. Sprayers that are not full multiple widths of the drill will not be able to use skip row systems unless the sprayer size is either increased or decreased to meet that requirement.

For more information about using skip-rows go to:

Adjusting Soybean Seeding Rates To Maximize Profit

Authors: Edwin Lentz, Jim Beuerlein

The cost per unit of soybean seed has been increasing steadily for ten years and will continue to do so as new traits are added to varieties. Because seed cost is a major production expense, it is important to use no more than necessary to produce the most profitable crop. The most profitable soybean seeding rate is determined by many factors including variety characteristics, soil productivity factors, cultural practices, weather during the growing season and finally, the interaction of the components of those major factors. In the final analysis, the plant population at harvest is the important factor, and is typically 60-80 percent of the seeding rate. Percent germination and emergence, loss to disease, and die-off due to plant competition determine the harvest population.

The most profitable plant population is a function of plant size, and the smaller the plants, the greater the number needed to maximize yield. For example, we need 30,000 corn plants, or 150,000 soybean plants or 1,500,000 wheat plants per acre for good yields. Therefore, the bigger the plant the fewer we need, and that rule also works for plant size within the soybean crop. A rule-of-thumb is: best yields are produced with about 100,000 plants 40 inches tall, or about 130,000 plants 30 inches tall, or about 170,000 plants that are 20 inches tall. The typical seeding rates needed to produce those populations are 125,000, 175,000 and 235,000 respectively.

Following are some factors that allow a reduction in seeding rate or require an increase in seeding rate for soybeans grown in 7.5-inch rows and starting with a seeding rate of 200,000 seeds per acre:

Reduce the seeding rate by: If:
75000 Plants are normally 40” tall at harvest
25000 Plants are normally 30” tall at harvest
20000 The soil has more than 2.5 % organic matter
20000 The seed has a fungicide treatment
20000 Tillage was used to prepare a seed bed
20000 Planting full season variety early
20000 The soil drainage is excessive (inadequate water)
15000 The soil drainage is very good (get more growth)
15000 Soil has a high water supplying capacity

If multiple factors apply, use the one allowing the lowest seeding rate.

Increase the seeding rate by: If:
50000 Planting the last half of June
35000 Plants normally are only 20” tall at harvest
25000 Planting the first half of June
25000 The soil has less than 2.0 % organic matter
25000 The soil has low fertility level
25000 Planting an early maturity variety
20000 The soil drainage is very poor
20000 Fields prone to soil crusting

If multiple factors apply, use the one allowing the highest seeding rate.


Fungicide Treated Soybean Seed Makes More Yield

Authors: Jim Beuerlein

Soybean diseases in Ohio have increased in number and severity over the past 10 years so that today, the loss of productivity from disease averages over $35,000,000 per year. The loss due to disease is greater than from any other factor except weather. The increase in soybean disease is due primarily to short crop rotations or no crop rotation and will be five to eight bushels per acre per year in many fields. During most years, several diseases are present but some are not recognized due to low levels of infection. By the time symptoms of a particular disease appear, the yield loss has already reached seven to ten percent. In many fields there is significant yield loss to disease even though no symptoms are evident.

In the past, we have relied on varieties’ disease resistance and tolerance to provide disease control. Many of the Phytophthora control genes are no longer effective because the pathogens have evolved and can overcome the genes’ defense mechanism. During the past ten years, we have relied more and more on fungicide seed treatments to improve soybean stands and increase the general health of soybean root systems following planting. During the past six years we have field-tested many of the seed treatment fungicides commonly used. All the tests were conducted in fields with very low disease pressure and no observable disease in the untreated check plots. Following are the results of thirty-six field trials evaluating the benefit of treating soybean seed with fungicides.

Year # Treatments Check Yield Avg with Fungicide Fungicide Yield Range
2001 10 56.9 58.6 57.8-60.6
2002 8 49.7 49.9 48.5-50.4
2003 9 49.7 53.1 50.1-53.8
2004 8 60.6 62.8 62.0-65.8
2005 8 56.5 56.5 55.1-57.8
2006 8 54.5 56.1 54.5-57.6
Average   54.7 56.2 54.7-57.7

Although all the test sites had a low potential for the development of root rot disease, there were yield increases when the seed was treated with fungicide. The average yield increase over the untreated check was 1.5 Bu/ac which is a value of about $10.50 per acre and 250% greater than the cost of seed treatment. Because many soybean fields in Ohio have a high potential for disease, and large yield losses, the routine use of seed treatment fungicides on soybeans is warranted and highly profitable. For more information on Fungicide seed treatment go to:

Fungicide Company Web Sites:
Bayer Crop Science


Soybean Inoculation Pays

Authors: Jim Beuerlein

Twelve years of evaluating soybean inoculation products consisting of 70 field trials and over 9000 research plots indicate that inoculating soybeans is a very profitable practice in Ohio. The average yield increase over the twelve years of testing in producer fields has returned a profit of over 300 percent. Field trials have been conducted using a corn/soybean crop rotation in fields with good soil pH and fertility, good surface and subsoil drainage, little disease pressure and high yield potential. Following are the tests results for the past six years:

Year # Treatments Check Yield Inoculation Treatment Yield Inoculation Yield Range
2001 14 56.4 58.5 58.1-59.4
2002 16 49.6 49.2 49.1-50.6
2003 17 50.0 51.5 50.5-52.6
2004 20 59.8 62.6 61.6-63.7
2005 19 55.2 56.9 55.7-58.6
2006 24 53.5 55.1 53.5-56.9
Averages   54.0 55.7 55.0-57.0

The average yield increase over the untreated check during the past six years was 1.7 Bu/ac which is a value of about $12.00 per acre and 300% greater than the cost of inoculation. The most productive products produced a profit of $18.00 per acre. For more information on soybean inoculation go to:

Inoculation Company Web Sites:
United Agri Products -
BeckerUnderwood -
Nitragin - www.emdcropbioscience
Philom Bios -
Sintesis Quimica -
BretYoung Seeds -
Advanced Biological Marketing -


Farm Forum in Piqua March 10th

Authors: Harold Watters

More speakers have been announced for Congressman's Boehner's Farm Forum on Saturday, at Edison State Community College in Piqua.

A distinguished panel of experts will join USDA Secretary, Mike Johanns, including Ohio farmer and president-elect of the National Pork Producers Council, Bryan Black, OSU Professor Carl Zulauf, Jim Wiesemeyer from Informa Economics, and Dave Juday, adjunct fellow with the Hudson Institute's Center for Global Food Issues and senior analyst with World Perspectives, Inc. The panel will discuss a wide range of issues at Farm Forum, including the 2007 Farm Bill.

This event provides an important opportunity to take a hard look at the issues facing the Ohio agriculture community. Boehner urges anyone with an interest in agriculture to participate in discussions this year. Plan to attend Saturday's Farm Forum at Edison State Community College, registration for this free meeting opens at 9:30 a.m. and the program will begin promptly at 10:00 a.m. To RSVP for this March 10th event, contact Congressman Boehner's district office toll-free at 1-800-582-1001.

Wrapping up Agricultural Pesticide Applicator Training for 2007

Authors: Harold Watters

With March comes the end of pesticide recertification for most agricultural pesticide applicators. If you have a private applicator license and this is your year to renew, then you must have at least three hours of recertification credits by March 31st and have paid the Ohio Department of Agriculture for your license renewal.

OSU Extension provides recertification education opportunities in all counties in Ohio. If you still need to sit through your educational classes for renewal – then check the OSU Extension Pesticide Education Website for final classes: Go to the website, click on Private Applicator, then on Recertification Opportunities. You may also contact your local OSU Extension office for more information.


Archive Issue Contributors: 

Peter Thomison (Corn Production), Anne Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Ron Hammond and Bruce Eisley (Entomology), Ed Lentz (Agronomy) and Jim Beuerlein (Soybean Production). Extension Agents: Roger Bender (Shelby), Howard Siecrist (Licking), Glen Arnold (Putnam), Keith Diedrick (Wayne), Todd Mangen (Mercer), Steve Prochaska (Crawford), Bruce Clevenger (Defiance), Greg LaBarge (Fulton), Mark Koenig (Sandusky) and Harold Watters (Champaign).

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.